Co-reporter:Damir Dzebo;Kasper Moth-Poulsen
Photochemical & Photobiological Sciences (2002-Present) 2017 vol. 16(Issue 8) pp:1327-1334
Publication Date(Web):2017/08/09
DOI:10.1039/C7PP00201G
We hereby present a simple method for reducing the effect of oxygen quenching in Triplet–Triplet Annihilation Upconversion (TTA-UC) systems. A number of commercially available thioethers and one thiol have been tested as singlet oxygen scavengers. Recording of the upconverted emission from a well-studied PdOEP (sensitizer)–DPA (annihilator/emitter) couple has been made over time with steady-state excitation capturing the steady-state kinetics of the TTA-UC process as the solubilized oxygen is depleted by reaction with the scavengers. The efficiency of the TTA-UC process is compared between chemical oxygen scavenging and mechanical removal by inert gas purging or the freeze–pump–thaw method. Selected methods are combined to explore the highest attainable TTA-UC quantum yield. A maximum TTA-UC quantum yield of 21% with the shortest UC onset time was obtained with dimethylthiomethane (DMTM) as the scavenger in an air-saturated solvent and slightly higher quantum yields were obtained in combination with other deoxygenation techniques. Samples containing DMTM displayed little decrease in the quantum yield over four hours of continuous high intensity irradiation, which illustrates the robustness of applying chemical oxygen removal in TTA-UC instead of more time-consuming mechanical processes that usually require specialized equipment.
Co-reporter:M. Shaali;J. G. Woller;P. G. Johansson;J. K. Hannestad;L. de Battice;N. Aissaoui;T. Brown;A. H. El-Sagheer;S. Kubatkin;S. Lara-Avila;B. Albinsson;A. Jesorka
Journal of Materials Chemistry C 2017 vol. 5(Issue 30) pp:7637-7643
Publication Date(Web):2017/08/03
DOI:10.1039/C7TC01015J
We demonstrate the use of arrays of Teflon AF nanopillars for directing the assembly of single rectangular DNA origami scaffolds, functionalized with covalently linked fluorophore molecules, in defined positions on patterned surfaces. This is achieved by introducing Teflon AF as a non-amplified negative e-beam resist, which is exposed and chemically developed to generate arrays of hydrophobic nanopillars with a minimum feature size 40 nm. Binding of the DNA origami to the pillars is facilitated by porphyrin moieties that act as hydrophobic molecular anchors, reaching 80% coverage of the available sites. This combination of top-down lithography and bottom-up self assembly is an efficient means of fabricating hierarchically structured bio-nanointerfaces in which the positioning of functional units is precisely controlled on the molecular scale inside the DNA assembly, and on the nanoscale at pre-designed locations on the substrate.
Co-reporter:Nesrine Aissaoui;Kasper Moth-Poulsen;Mikael Käll;Peter Johansson;L. Marcus Wilhelmsson
Nanoscale (2009-Present) 2017 vol. 9(Issue 2) pp:673-683
Publication Date(Web):2017/01/05
DOI:10.1039/C6NR04852H
Here we investigate the energy transfer rates of a Förster resonance energy transfer (FRET) pair positioned in close proximity to a 5 nm gold nanoparticle (AuNP) on a DNA origami construct. We study the distance dependence of the FRET rate by varying the location of the donor molecule, D, relative to the AuNP while maintaining a fixed location of the acceptor molecule, A. The presence of the AuNP induces an alteration in the spontaneous emission of the donor (including radiative and non-radiative rates) which is strongly dependent on the distance between the donor and AuNP surface. Simultaneously, the energy transfer rates are enhanced at shorter D–A (and D–AuNP) distances. Overall, in addition to the direct influence of the acceptor and AuNP on the donor decay there is also a significant increase in decay rate not explained by the sum of the two interactions. This leads to enhanced energy transfer between donor and acceptor in the presence of a 5 nm AuNP. We also demonstrate that the transfer rate in the three “particle” geometry (D + A + AuNP) depends approximately linearly on the transfer rate in the donor–AuNP system, suggesting the possibility to control FRET process with electric field induced by 5 nm AuNPs close to the donor fluorophore. It is concluded that DNA origami is a very versatile platform for studying interactions between molecules and plasmonic nanoparticles in general and FRET enhancement in particular.
Co-reporter:Damir Dzebo, Karl Börjesson, Victor Gray, Kasper Moth-Poulsen, and Bo Albinsson
The Journal of Physical Chemistry C 2016 Volume 120(Issue 41) pp:23397-23406
Publication Date(Web):September 22, 2016
DOI:10.1021/acs.jpcc.6b07920
An important challenge when developing materials for triplet–triplet annihilation upconversion (TTA-UC) is achieving efficient and well-functioning solid-state systems. We here explore the effect of intramolecular TTA in oligomers and dendrimers based on the 9,10-diphenylanthracene (DPA) chromophore. The macromolecules are sensitized using palladium porphyrin, both in solution and in solid poly(methyl methacrylate) (PMMA), demonstrating a positive effect on overall upconversion in the solid state correlating with the well-controlled size of the DPA constructs. The UC kinetics is modeled and fit to steady-state and time-resolved emission data to give further insight into the intramolecular excited-state migration and annihilation in the macromolecular annihilator systems.
Co-reporter:Mélina Gilbert and Bo Albinsson
Chemical Society Reviews 2015 vol. 44(Issue 4) pp:845-862
Publication Date(Web):12 Sep 2014
DOI:10.1039/C4CS00221K
Exploring charge and energy transport in donor–bridge–acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor–bridge–acceptor (D–B–A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the “molecular wire”). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor–acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor–acceptor electronic coupling and transfer rates. Several examples of donor–bridge–acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed.
Co-reporter:Mélina Gilbert Gatty, Axel Kahnt, Louisa J. Esdaile, Marie Hutin, Harry L. Anderson, and Bo Albinsson
The Journal of Physical Chemistry B 2015 Volume 119(Issue 24) pp:7598-7611
Publication Date(Web):March 9, 2015
DOI:10.1021/jp5115064
Achieving long-range charge transport in molecular systems is interesting to foresee applications of molecules in practical devices. However, designing molecular systems with pre-defined wire-like properties remains difficult due to the lack of understanding of the mechanism for charge transfer. Here we investigate a series of porphyrin oligomer-bridged donor–acceptor systems Fc–Pn–C60 (n = 1–4, 6). In these triads, excitation of the porphyrin-based bridge generates the fully charge-separated state, Fc•+–Pn–C60•-, through a sequence of electron transfer steps. Temperature dependence of both charge separation (Fc–Pn*–C60 → Fc–Pn•+–C60•-) and recombination (Fc•+–Pn–C60•– → Fc–Pn–C60) processes was probed by time-resolved fluorescence and femtosecond transient absorption. In the long triads, two mechanisms contribute to recombination of Fc•+–Pn–C60•– to the ground state. At high temperatures (≥280 K), recombination via tunneling dominates for the entire series. At low temperatures (<280 K), unusual crossover from tunneling to hopping occurs in long triads. This crossover is rationalized by the increased lifetimes of Fc•+–Pn–C60•–, hence the higher probability of reforming Fc–Pn•+–C60•– during recombination. We demonstrate that at 300 K, the weak distance dependence for charge transfer (β = 0.028 Å–1) relies on tunneling rather than hopping.
Co-reporter:Giuseppe Sforazzini ; Axel Kahnt ; Michael Wykes ; Johannes K. Sprafke ; Sergio Brovelli ; Damien Montarnal ; Francesco Meinardi ; Franco Cacialli ; David Beljonne ; Bo Albinsson ;Harry L. Anderson
The Journal of Physical Chemistry C 2014 Volume 118(Issue 8) pp:4553-4566
Publication Date(Web):February 3, 2014
DOI:10.1021/jp500624q
Conjugated polyrotaxanes jacketed with hole-transport groups have been synthesized from water-soluble polyrotaxanes consisting of a polyfluorene-alt-biphenylene (PFBP) conjugated polymer threaded through β-cyclodextrin macrocycles. The hydroxyl groups of the oligosaccharides were efficiently functionalized with triphenylamine (TPA) so that every polyrotaxane molecule carries a coat of about 200 TPA units, forming a supramolecular coaxial structure. This architecture was characterized using a range of techniques, including small-angle X-ray scattering. Absorption of light by the TPA units results in excitation energy transfer (EET) and photoinduced electron transfer (ET) to the inner conjugated polymer core. These energy- and charge-transfer processes were explored by steady-state and time-resolved fluorescence spectroscopy, femtosecond transient absorption spectroscopy, and molecular modeling. The time-resolved measurements yielded insights into the heterogeneity of the TPA coat: those TPA units which are close to the central polymer core tend to undergo ET, whereas those on the outer surface of the polyrotaxane, far from the core, undergo EET. Sections of the backbone that are excited indirectly via EET tend to be more remote from the TPA units and thus are less susceptible to electron-transfer quenching. The rate of EET from the TPA units to the PFBP core was effectively modeled by taking account of the heterogeneity in the TPA–PFBP distance, using a distributed monopole approach. This work represents a new strategy for building and studying well-defined arrays of >100 covalently linked chromophores.
Co-reporter:Jakob G. Woller ; Jonas K. Hannestad
Journal of the American Chemical Society 2013 Volume 135(Issue 7) pp:2759-2768
Publication Date(Web):January 25, 2013
DOI:10.1021/ja311828v
Mimicking green plants’ and bacteria’s extraordinary ability to absorb a vast number of photons and harness their energy is a longstanding goal in artificial photosynthesis. Resonance energy transfer among donor dyes has been shown to play a crucial role on the overall transfer of energy in the natural systems. Here, we present artificial, self-assembled, light-harvesting complexes consisting of DNA scaffolds, intercalated YO-PRO-1 (YO) donor dyes and a porphyrin acceptor anchored to a lipid bilayer, conceptually mimicking the natural light-harvesting systems. A model system consisting of 39-mer duplex DNA in a linear wire configuration with the porphyrin attached in the middle of the wire is primarily investigated. Utilizing intercalated donor fluorophores to sensitize the excitation of the porphyrin acceptor, we obtain an effective absorption coefficient 12 times larger than for direct excitation of the porphyrin. On the basis of steady-state and time-resolved emission measurements and Markov chain simulations, we show that YO-to-YO resonance energy transfer substantially contributes to the overall flow of energy to the porphyrin. This increase is explained through energy migration along the wire allowing the excited state energy to transfer to positions closer to the porphyrin. The versatility of DNA as a structural material is demonstrated through the construction of a more complex, hexagonal, light-harvesting scaffold yielding further increase in the effective absorption coefficient. Our results show that, by using DNA as a scaffold, we are able to arrange chromophores on a nanometer scale and in this way facilitate the assembly of efficient light-harvesting systems.
Co-reporter:Mélina Gilbert, Louisa J. Esdaile, Marie Hutin, Katsutoshi Sawada, Harry L. Anderson, and Bo Albinsson
The Journal of Physical Chemistry C 2013 Volume 117(Issue 50) pp:26482-26492
Publication Date(Web):November 27, 2013
DOI:10.1021/jp4098342
The rate of the photoinduced charge-separation in C60-terminated butadiyne-linked porphyrin oligomers Pn (n = 4, 6) is strongly influenced by their molecular conformation. In these systems, the presence of the butadiyne linkers gives rise to a broad distribution of conformations in the ground state, due to an almost barrierless rotation of individual porphyrin units in the oligomer chain. The conformational states of these oligomers, either twisted or planar, could be selected by varying the excitation wavelength, thereby providing different initial excited states for charge separation. Charge separation in the different conformers was followed using both steady-state and 2D time-resolved emission using a streak camera system. Singular value decomposition (SVD) analysis applied on streak camera data provides here a powerful tool to study the conformational dependence of the charge separation in long PnC60 systems. Both the kinetics and spectral changes accompanying charge separation could be analyzed for different populations of conformation. From this analysis we show that, for both systems studied, twisted conformations undergo faster charge separation than planar conformations. This disparity in charge separation rates was ascribed mainly to the difference in driving force for charge separation between twisted and planar conformations. Charge separation was also studied in oligomers PnC60 coordinated to an octadentate ligand T8 that hinders the rotation of porphyrin subunits. The semicircular complexes PnC60-T8 show dramatic changes in their spectral properties, as well as slow excitation wavelength independent rate of charge separation and corresponding low efficiency compared to their linear counterparts. This slow charge separation rate was attributed to fast relaxation to the lowest excited vibronic state and lack of driving force for charge separation in these close to planar semicircular systems; i.e., the template systems behave like “normal” donor–acceptor systems without slow conformational relaxation. This work illustrates how control of conformation can be used to tune the rate of charge separation.
Co-reporter:Bo Albinsson, Jonas K. Hannestad, Karl Börjesson
Coordination Chemistry Reviews 2012 Volume 256(21–22) pp:2399-2413
Publication Date(Web):November 2012
DOI:10.1016/j.ccr.2012.02.024
Mimicking natural photosynthesis by covalently arranging antenna and charge separation units is a formidable task. Many such beautiful supramolecular complexes have been designed and synthesized with large efforts, some of which are presented in this special issue. The ability to predict relative position of and electronic coupling between the active components in covalent arrays is quite high but there are two obvious drawbacks with the covalent approach. Firstly, as the size grows the complexity of the organic synthesis increases and secondly, sensitivity to light-induced damage becomes a major issue if covalent bonds are broken. Self-assembly of the photoactive components should, in principle, provide a solution to both these issues but generally the ability to predict position and electronic coupling is too low to have the designed properties needed for a functional artificial photosynthetic complex. Here, we present an approach of using DNA as a template for arranging both charge separation units and antenna molecules that govern long-range energy transfer. Of particular interest is the ability of DNA to function as a scaffold for chromophores, either through covalent attachment, or through non-covalent association by means of intercalation or grove binding. Using controlled positioning of dyes, multichromophoric assemblies can be created, capable of long range communication through multi-step energy transfer. This facilitates creation of DNA-based photonic devices for both light harvesting and directed information transfer. The channeled excitation energy can be transformed site specifically to chemical energy by charge separation of DNA linked porphyrins. A two phase system is discussed, in which the DNA is located in buffered solution whereas the hydrophobic porphyrins, responsible for the charge separation reaction, are located in the lipid bilayer of liposomes or supported lipid bilayers.Highlights► DNA structures as scaffolds for chromophores and redox centers. ► A novel architecture for artificial photosynthesis. ► Surface bound DNA nanostructures. ► Long range FRET through DNA assembled fluorophores.
Co-reporter:Karl Börjesson, Jakob G. Woller, Elham Parsa, Jerker Mårtensson and Bo Albinsson
Chemical Communications 2012 vol. 48(Issue 12) pp:1793-1795
Publication Date(Web):14 Dec 2011
DOI:10.1039/C2CC17434K
A binding pocket consisting of two zinc porphyrins self assembled by Watson-Crick base pairing is presented. The porphyrin binding pocket is located in the confined environment of a lipid membrane whereas the DNA is located in the water phase. Bidentate electron accepting ligands are shown to coordinate in-between the two porphyrins.
Co-reporter:Joakim Kärnbratt, Mélina Gilbert, Johannes K. Sprafke, Harry L. Anderson, and Bo Albinsson
The Journal of Physical Chemistry C 2012 Volume 116(Issue 37) pp:19630-19635
Publication Date(Web):August 22, 2012
DOI:10.1021/jp306237e
Conjugated zinc porphyrin oligomers of various lengths are shown to form well-defined planar aggregates at low temperatures. The aggregation occurs over a narrow temperature interval (170–150 K) and is accompanied by dramatic changes in the electronic absorption and emission spectra. Similar changes are found in J-aggregates in which the transition dipole moments of aggregated chromophores couple to form a new and intense transition in the absorption spectrum, red shifted from the monomeric chromophore band. For the present porphyrin oligomers, the dramatic absorption changes are not associated with the formation of large aggregates, but rather with the dimerization accompanied by planarization of the oligomers. Free oligomers have a broad distribution of porphyrin–porphyrin dihedral angles and show a broad and unstructured absorption spectrum. As the oligomers stack to form aggregates, they planarize and the width of the conformational distribution is reduced to include virtually only the planar conformers, resulting in the observed change of the absorption spectrum. No experimental evidence for the formation of large aggregates was found, while a small aggregate, probably only dimer, is supported by the minor changes of the fluorescence rate constant upon aggregation and the fact that pyridine has no significant effect on the formation of this aggregate, which otherwise is very effective for inhibiting aggregation of zinc porphyrin oligomers. Compared to most porphyrin aggregates, which show broad absorption spectra and quenched fluorescence, these aggregates give sharp absorption and emission spectra with little change in the fluorescence quantum yield. Similar aggregates were also observed for oligomers substituted with both a fullerene electron acceptor and a ferrocene donor. The results presented here will be potentially useful as tools to understand how electron transfer and delocalization processes are influenced by molecular order/disorder transitions.
Co-reporter:Jakob G. Woller, Karl Börjesson, Sofia Svedhem, and Bo Albinsson
Langmuir 2012 Volume 28(Issue 4) pp:1944-1953
Publication Date(Web):December 27, 2011
DOI:10.1021/la2039976
The binding of zinc–porphyrin-anchored linear DNA to supported lipid membranes was studied using quartz crystal microbalance with dissipation monitoring (QCM-D). The hydrophobic anchor is positioned at the ninth base of 39-base-pair-long DNA sequences, ensuring that the DNA is positioned parallel to the membrane surface when bound, an important prerequisite for using this type of construct for the creation of two-dimensional (2D) DNA patterns on the surface. The anchor consists of a porphyrin group linked to the DNA via two or three phenylethynylene moieties. Double-stranded DNA where one of the strands was modified with either of these anchors displayed irreversible binding, although binding to the membrane was faster for the derivatives with the short anchor. The binding and subsequent hybridization of single-stranded constructs on the surface was demonstrated at 60 °C, for both anchors, revealing a coverage-dependent behavior. At low coverage, hybridization results in an increase in mass (as measured by QCM-D) by a factor of ∼1.5, accompanied by a slight increase in the rigidity of the DNA layer. At high coverage, hybridization expels molecules from the membrane, associated with an initial increase, followed by a decrease in DNA mass (as detected both by QCM-D and by an optical technique). Melting of the DNA on the surface was performed, followed by rehybridization of the single-stranded species left on the surface with their complementary strand, demonstrating the reversibility inherent in using DNA for the formation of membrane-confined nanopatterns.
Co-reporter:Axel Kahnt ; Joakim Kärnbratt ; Louisa J. Esdaile ; Marie Hutin ; Katsutoshi Sawada ; Harry L. Anderson
Journal of the American Chemical Society 2011 Volume 133(Issue 25) pp:9863-9871
Publication Date(Web):May 19, 2011
DOI:10.1021/ja2019367
Electron-transfer reactions are fundamental to many practical devices, but because of their complexity, it is often very difficult to interpret measurements done on the complete device. Therefore, studies of model systems are crucial. Here the rates of charge separation and recombination in donor–acceptor systems consisting of a series of butadiyne-linked porphyrin oligomers (n = 1–4, 6) appended to C60 were investigated. At room temperature, excitation of the porphyrin oligomer led to fast (5–25 ps) electron transfer to C60 followed by slower (200–650 ps) recombination. The temperature dependence of the charge-separation reaction revealed a complex process for the longer oligomers, in which a combination of (i) direct charge separation and (ii) migration of excitation energy along the oligomer followed by charge separation explained the observed fluorescence decay kinetics. The energy migration is controlled by the temperature-dependent conformational dynamics of the longer oligomers and thereby limits the quantum yield for charge separation. Charge recombination was also studied as a function of temperature through measurements of femtosecond transient absorption. The temperature dependence of the electron-transfer reactions could be successfully modeled using the Marcus equation through optimization of the electronic coupling (V) and the reorganization energy (λ). For the charge-separation rate, all of the donor–acceptor systems could be successfully described by a common electronic coupling, supporting a model in which energy migration is followed by charge separation. In this respect, the C60-appended porphyrin oligomers are suitable model systems for practical charge-separation devices such as bulk-heterojunction solar cells, where conformational disorder strongly influences the electron-transfer reactions and performance of the device.
Co-reporter:Dr. Karl Börjesson;Erik P. Lundberg;Jakob G. Woller; Bengt Nordén ; Bo Albinsson
Angewandte Chemie 2011 Volume 123( Issue 36) pp:8462-8465
Publication Date(Web):
DOI:10.1002/ange.201103338
Co-reporter:Dr. Karl Börjesson;Erik P. Lundberg;Jakob G. Woller; Bengt Nordén ; Bo Albinsson
Angewandte Chemie International Edition 2011 Volume 50( Issue 36) pp:8312-8315
Publication Date(Web):
DOI:10.1002/anie.201103338
Co-reporter:Bo Albinsson and Jerker Mårtensson
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 27) pp:7338-7351
Publication Date(Web):16 Jun 2010
DOI:10.1039/C003805A
This perspective will focus on the mechanistic aspects of singlet and triplet excitation energy transfer. Well defined donor–bridge–acceptor systems specifically designed for investigating the distance and energy gap dependencies of the energy transfer reactions are discussed along with some recent developments in computational modeling of the electronic coupling.
Co-reporter:Søren Preus, Kristine Kilså, L. Marcus Wilhelmsson and Bo Albinsson
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 31) pp:8881-8892
Publication Date(Web):08 Jun 2010
DOI:10.1039/C000625D
Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of the fluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour of these probes in nucleic acid environments, but will also be profitable in the development of new and improved fluorescent base analogues. Here, temperature-dependent fluorescence quantum yield measurements are used to successfully separate and quantify the temperature-dependent and temperature-independent non-radiative excited-state decay processes of the three nucleobase analogues tC, tCO and tCnitro; all of which are derivatives of a phenothiazine or phenoxazine tricyclic framework. These results strongly suggest that the non-radiative decay process dominating the fast deactivation of tCnitro is an internal conversion of a different origin than the decay pathways of tC and tCO. tCnitro is reported to be fluorescent only in less dipolar solvents at room temperature, which is explained by an increase in excited-state dipole moment along the main non-radiative decay pathway, a suggestion that applies in the photophysical discussion of large polycyclic nitroaromatics in general. New insight into the ground and excited-state potential energy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFT calculations. The S0 potential energy surfaces of tC and tCnitro possess two global minima corresponding to geometries folded along the middle sulfur–nitrogen axis separated by an energy barrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potential energy surface of tCO is also predicted to be shallow along the bending coordinate but with an equilibrium geometry corresponding to the planar conformation of the tricyclic framework, which may explain some of the dissimilar properties of tC and tCO in various confined (biological) environments. The S1 equilibrium geometries of all three base analogues are predicted to be planar. These results are discussed in the context of the tC bases positioned in double-stranded DNA scenarios.
Co-reporter:Karl Börjesson, Joanna Wiberg, Afaf H. El-Sagheer, Thomas Ljungdahl, Jerker Mårtensson, Tom Brown, Bengt Nordén, and Bo Albinsson
ACS Nano 2010 Volume 4(Issue 9) pp:5037
Publication Date(Web):September 1, 2010
DOI:10.1021/nn100667b
We have synthesized and studied a supramolecular system comprising a 39-mer DNA with porphyrin-modified thymidine nucleosides anchored to the surface of large unilamellar vesicles (liposomes). Liposome porphyrin binding characteristics, such as orientation, strength, homogeneity, and binding site size, was determined, suggesting that the porphyrin is well suited as a photophysical and redox-active lipid anchor, in comparison to the inert cholesterol anchor commonly used today. Furthermore, the binding characteristics and hybridization capabilities were studied as a function of anchor size and number of anchoring points, properties that are of importance for our future plans to use the addressability of these redox-active nodes in larger DNA-based nanoconstructs. Electron transfer from photoexcited porphyrin to a lipophilic benzoquinone residing in the lipid membrane was characterized by steady-state and time-resolved fluorescence and verified by femtosecond transient absorption.Keywords: DNA; electron transfer; membrane; nanotechnology; porphyrin; supramolecular
Co-reporter:Mattias P. Eng, Bo Albinsson
Chemical Physics 2009 Volume 357(1–3) pp:132-139
Publication Date(Web):23 February 2009
DOI:10.1016/j.chemphys.2008.12.004
Abstract
The attenuation factor, β, for the distance dependence of electron exchange reactions is a sensitive function of the donor–bridge energy gap and bridge conformation. In this work the electronic coupling for electron and triplet excitation energy transfer has been investigated for five commonly used repeating bridge structures. The investigated bridge structures are OF (oligo fluorene), OP (oligo phenylene), OPE (oligo p-phenyleneethynylene), OPV (oligo phenylenevinylene), and OTP (oligo thiophene). Firstly, the impact of the donor–bridge energy gap was investigated by performing calculations with a variety of donors appended onto bridges that were kept in a planar conformation. This resulted in, to our knowledge, the first presented sets of bridge specific parameters to be inserted into the commonly used McConnell model. Secondly, since at experimental conditions large conformational flexibility is expected, a previously developed model that takes conformational disorder of the bridge into account has been applied to the investigated systems [M.P. Eng, T. Ljungdahl, J. Mårtensson, B. Albinsson, J. Phys. Chem. B 110 (2006) 6483]. This model is based on Boltzmann averaging and has been shown to describe the temperature dependence of the attenuation factor through OPE-bridges. Together, the parameters describing the donor–bridge energy gap dependence, for planar bridge structures, and the Boltzmann averaging procedure, describing the impact of rotational disorder, have the potential to a priori predict attenuation factors for electron and excitation energy transfer reactions through bridged donor–acceptor systems.
Co-reporter:Bo Albinsson, Jerker Mårtensson
Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2008 Volume 9(Issue 3) pp:138-155
Publication Date(Web):September 2008
DOI:10.1016/j.jphotochemrev.2008.01.002
Donor–bridge–acceptor (D-B-A) systems, either as supermolecules or on surfaces, have been extensively studied with respect to long-range electron (ET) and excitation energy (EET) transfer. In more recent years, the main research objective has been to develop knowledge on how to construct molecular-based devices, with predetermined electron transfer properties, intended for application in electronics and photovoltaics. At present, such construction is in general hampered for several reasons. Most importantly, the property of a D-B-A system is not a simple linear combination of properties of the individual components, but depends on the specific building blocks and how they are assembled. An important example is the ability of the bridge to support the intended transfer process. The mediation of the transfer is characterized by an attenuation factor, β, often viewed as a bridge specific constant but which also depends on the donor and the acceptor, i.e. the same bridge can either be poorly or strongly conducting depending on the donor and acceptor. This review gives an account of the experimental exploration of the attenuation factor β in a series of bis(porphyrin) systems covalently linked by bridges of the oligo(phenyleneethynylene) (OPE) type. Attenuation factors for ET as well as for both singlet and triplet EET are discussed. A report is also given on the dependence of the transfer efficiency on the energy-gap between the donor and bridge states relevant for the specific transfer process. The experimental variation of β with varying donor and acceptor components is shown for a range of conjugated bridges by representative examples from the literature. The theoretical rationalization for the observed variation is briefly discussed. Based on the Gamow tunneling model, the observed variations in β-values with varying donors and acceptors for the same bridges is simulated successfully simultaneously as the observed energy-gap dependence is modelled.
Co-reporter:MattiasP. Eng Dr.;Jerker Mårtensson Dr.
Chemistry - A European Journal 2008 Volume 14( Issue 9) pp:2819-2826
Publication Date(Web):
DOI:10.1002/chem.200701477
Abstract
A series of donor-bridge-acceptor (D-B-A) systems with varying donor–acceptor distances has been studied with respect to the temperature dependence of the triplet excitation energy transfer (TEET) rates. The donor and acceptor, zinc(II) and free-base porphyrin, respectively, were separated by oligo-p-phenyleneethynylene (OPE) bridges, where the number of phenyleneethynylene groups was varied between two and five, giving rise to edge-to-edge separations ranging between 12.7 and 33.4 Å. The study was performed in 2-MTHF between room temperature and 80 K. It was found that the distance dependence was exponential, in line with the McConnell model, and the attenuation factor, β, was temperature dependent. The experimentally determined temperature dependence of β was evaluated by using a previously derived model for the conformational dependence of the electronic coupling based on results from extensive quantum chemical, DFT and time-dependent DFT (TD-DFT), calculations. Two regimes in the temperature interval could be identified: one high-temperature, low-viscosity regime, and one low-temperature, high-viscosity regime. In the first regime, the temperature dependence of β was, according to the model, well described by a Boltzmann conformational distribution. In the latter, the molecular motions that govern the electronic coupling are slowed down to the same order of magnitude as the TEET rates. This, in effect, leads to a distortion of the conformational distribution. In the high-temperature regime the model could reproduce the temperature dependence of β, and the extracted rotational barrier between two neighboring phenyl units of the bridge structure, Ei=1.1 kJ mol−1, was in line with previous experimental and theoretical studies. After inclusion of parameters that take the viscosity of the medium into account, successful modeling of the experimentally observed temperature dependence of the distance dependence was achieved over the whole temperature interval.
Co-reporter:Bo Albinsson, Mattias P. Eng, Karin Pettersson and Mikael U. Winters
Physical Chemistry Chemical Physics 2007 vol. 9(Issue 44) pp:5847-5864
Publication Date(Web):17 Jul 2007
DOI:10.1039/B706122F
Electron and energy transfer reactions in covalently connected donor–bridge–acceptor assemblies are strongly dependent, not only on the donor–acceptor distance, but also on the electronic structure of the bridge. In this article we describe some well characterised systems where the bridges are π-conjugated chromophores, and where, specifically, the interplay between bridge length and energy plays an important role for the donor–acceptor electronic coupling. For any application that relies on the transport of electrons, for example molecule based solar cells or molecular scale electronics, it will be imperative to predict the electron transfer capabilities of different molecular structures. The potential difficulties with making such predictions and the lack of suitable models are also discussed.
Co-reporter:Mikael U. Winters;Joakim Kärnbratt;Holly E. Blades;Craig J. Wilson Dr.;Michael J. Frampton Dr.;Harry L. Anderson
Chemistry - A European Journal 2007 Volume 13(Issue 26) pp:
Publication Date(Web):21 JUN 2007
DOI:10.1002/chem.200700434
A donor–acceptor system is presented in which the electron-transfer rates can be sensitively controlled by means of excitation wavelength and temperature. The electron donor is a butadiyne-linked zinc porphyrin dimer that is connected to a C60 electron acceptor. The broad distribution of conformations allowed by the butadiyne linker makes it possible to selectively excite perpendicular or planar donor conformers and thereby prepare separate initial states with driving forces for electron transfer that differ by almost 0.2 eV. This, as well as significant differences in electronic coupling, leads to distinctly different rate constants for electron transfer, which in consequence can be controlled by changing excitation wavelength. By extending the system with a secondary donor (ferrocene), a second, long-range charge-separated state can be formed. This system has been used to test the influence of conformational heterogeneity on electron transfer mediated by the porphyrin dimer in the ground state. It was found that if the dimer is forced to a planar conformation by means of a bidentate ligand, the charge recombination rate increased by an order of magnitude relative to the unconstrained system. This illustrates how control of conformation of a molecular wire can affect its behaviour.
Co-reporter:Mattias P. Eng
Angewandte Chemie International Edition 2006 Volume 45(Issue 34) pp:
Publication Date(Web):26 JUL 2006
DOI:10.1002/anie.200601379
Donor chromophores attached to oligo(phenyleneethynylene) molecular bridges of varying length have attenuation factors for electron tunneling β that vary systematically with the donor–bridge (DB) energy gap (see picture). Investigations show that for bridges with ethynylene and vinylene repeating subunits, the electronic coupling increases with increasing donor–acceptor (DA) distance. A simple model accounts for this unexpected observation.
Co-reporter:Mattias P. Eng
Angewandte Chemie 2006 Volume 118(Issue 34) pp:
Publication Date(Web):26 JUL 2006
DOI:10.1002/ange.200601379
Für Donorchromophore an unterschiedlich langen molekularen Oligo(phenylenethinylen)-Brücken variieren die Schwächungsfaktoren β des Elektronentunnelns systematisch mit der Energielücke zwischen Donor (D) und Brücke (B, siehe Bild). Im Fall von Brücken mit Ethinylen- und Vinylen-Wiederholungseinheiten steigt die elektronische Kopplung mit dem Donor-Acceptor(DA)-Abstand. Ein einfaches Modell erklärt diese unerwartete Entdeckung.
Co-reporter:Søren Preus, Kristine Kilså, L. Marcus Wilhelmsson and Bo Albinsson
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 31) pp:NaN8892-8892
Publication Date(Web):2010/06/08
DOI:10.1039/C000625D
Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of the fluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour of these probes in nucleic acid environments, but will also be profitable in the development of new and improved fluorescent base analogues. Here, temperature-dependent fluorescence quantum yield measurements are used to successfully separate and quantify the temperature-dependent and temperature-independent non-radiative excited-state decay processes of the three nucleobase analogues tC, tCO and tCnitro; all of which are derivatives of a phenothiazine or phenoxazine tricyclic framework. These results strongly suggest that the non-radiative decay process dominating the fast deactivation of tCnitro is an internal conversion of a different origin than the decay pathways of tC and tCO. tCnitro is reported to be fluorescent only in less dipolar solvents at room temperature, which is explained by an increase in excited-state dipole moment along the main non-radiative decay pathway, a suggestion that applies in the photophysical discussion of large polycyclic nitroaromatics in general. New insight into the ground and excited-state potential energy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFT calculations. The S0 potential energy surfaces of tC and tCnitro possess two global minima corresponding to geometries folded along the middle sulfur–nitrogen axis separated by an energy barrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potential energy surface of tCO is also predicted to be shallow along the bending coordinate but with an equilibrium geometry corresponding to the planar conformation of the tricyclic framework, which may explain some of the dissimilar properties of tC and tCO in various confined (biological) environments. The S1 equilibrium geometries of all three base analogues are predicted to be planar. These results are discussed in the context of the tC bases positioned in double-stranded DNA scenarios.
Co-reporter:Bo Albinsson, Mattias P. Eng, Karin Pettersson and Mikael U. Winters
Physical Chemistry Chemical Physics 2007 - vol. 9(Issue 44) pp:NaN5864-5864
Publication Date(Web):2007/07/17
DOI:10.1039/B706122F
Electron and energy transfer reactions in covalently connected donor–bridge–acceptor assemblies are strongly dependent, not only on the donor–acceptor distance, but also on the electronic structure of the bridge. In this article we describe some well characterised systems where the bridges are π-conjugated chromophores, and where, specifically, the interplay between bridge length and energy plays an important role for the donor–acceptor electronic coupling. For any application that relies on the transport of electrons, for example molecule based solar cells or molecular scale electronics, it will be imperative to predict the electron transfer capabilities of different molecular structures. The potential difficulties with making such predictions and the lack of suitable models are also discussed.
Co-reporter:Karl Börjesson, Jakob G. Woller, Elham Parsa, Jerker Mårtensson and Bo Albinsson
Chemical Communications 2012 - vol. 48(Issue 12) pp:NaN1795-1795
Publication Date(Web):2011/12/14
DOI:10.1039/C2CC17434K
A binding pocket consisting of two zinc porphyrins self assembled by Watson-Crick base pairing is presented. The porphyrin binding pocket is located in the confined environment of a lipid membrane whereas the DNA is located in the water phase. Bidentate electron accepting ligands are shown to coordinate in-between the two porphyrins.
Co-reporter:Bo Albinsson and Jerker Mårtensson
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 27) pp:NaN7351-7351
Publication Date(Web):2010/06/16
DOI:10.1039/C003805A
This perspective will focus on the mechanistic aspects of singlet and triplet excitation energy transfer. Well defined donor–bridge–acceptor systems specifically designed for investigating the distance and energy gap dependencies of the energy transfer reactions are discussed along with some recent developments in computational modeling of the electronic coupling.
Co-reporter:Mélina Gilbert and Bo Albinsson
Chemical Society Reviews 2015 - vol. 44(Issue 4) pp:NaN862-862
Publication Date(Web):2014/09/12
DOI:10.1039/C4CS00221K
Exploring charge and energy transport in donor–bridge–acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor–bridge–acceptor (D–B–A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the “molecular wire”). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor–acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor–acceptor electronic coupling and transfer rates. Several examples of donor–bridge–acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed.
![[1,1':3',1''-Terphenyl]-4,4''-dicarboxylic acid](/data/chemimg/470700/13215-72-0.png)
![[1,1':3',1''-Terphenyl]-4,4''-dicarboxylic acid](/data/chemimg/470700/13215-72-0_b.png)