This advanced undergraduate chemistry laboratory exercise takes advantage of the unique spectroscopic properties of the free radical chlorine dioxide to allow for a direct comparison of its symmetric stretch in both the ground and excited states. It incorporates several subject areas covered in an undergraduate chemistry degree (synthesis, spectroscopy, and computational chemistry) and is suitable for an advanced level inorganic, physical, or integrated chemistry laboratory course. Students synthesize aqueous chlorine dioxide, analyze a vibronic progression of the symmetric stretch in the excited state using UV–vis spectroscopy, and also record the energy of the symmetric stretch in the ground state using Raman spectroscopy. In addition to offering advanced undergraduate students the opportunity to study the chemistry of a radical first-hand, this exercise also reinforces the use of synthetic techniques for the purpose of studying how a molecule’s physical properties vary with the electronic state. An optional computational chemistry component includes optimizing the geometries of the ground and excited states of the radical, calculating the charge, and comparing computed harmonic vibrational frequencies to the experimental data.Keywords: Computational Chemistry; Hands-On Learning/Manipulatives; Inorganic Chemistry; Interdisciplinary/Multidisciplinary; Laboratory Instruction; Physical Chemistry; Spectroscopy; Synthesis; Upper-Division Undergraduate;

•CCC-NHC nickel pincer complexes were synthesised by metallation/transmetallation.•Raman was obtained for the chloride complex along with a simulated spectrum.•Cationic CCC-NHC pincer nickel complexes were made which exhibited polymorphism.•Coupling of NHC's from two different ligands, which were oxidized.The metallation/transmetallation strategy has been successfully applied to the preparation of CCC-NHC pincer nickel complexes. Manipulation of the coordination sphere lead to cationic CCC-NHC pincer nickel complexes. These were found to exhibit polymorphism in the solid state with significant differences in the intermolecular distances observed by X-ray crystallography. Three polymorphs were observed for the PF6− salt, and two were observed for the BF4− salt. When BPh4− was the counterion only one morphology was observed, and crystals grown of the triflate salt were too small for analysis. Details of the differences are documented for comparison. Additionally, during crystallization it was found that a rearrangement of the CCC-NHC ligand had occurred, involving coupling of an NHC from two different ligands, which were oxidized.Polymorph packing differences.Download high-res image (164KB)Download full-size image

•Double carboxylic acid acceptor quinoxaline dyes have been synthesized.•Double anchor dyes bind metal oxides notably stronger than single anchor dyes.•All dyes show efficient electron injection into a semiconductor.•This strategy enables multi-components to be anchored in devices with simple acids.Strong anchoring groups are essential in the fabrication of the highest efficiency dye-sensitized solar cell (DSC) devices and for promoting long-term stability of photosensitizers in DSCs. While many metal-based sensitizers frequently make use of multiple anchors, synthesizing purely organic dyes with multiple anchors, especially those with anchors in direct conjugation with donor structures, has proved challenging. Novel quinoxaline-based dyes utilizing double donor/double acceptor structures can fill this gap in dye design understanding through a novel double donor-π-bridge-double acceptor (DD-π-AA) dye. These dyes have been synthesized with the optical and electrochemical properties, electron injection efficiencies, and relative binding strengths characterized. Fluorescence lifetime measurements show favorable electron injections from all dyes. Submersing dye-sensitized TiO2 plates in a hydrolytic solution reveals desorption rates up to 180 times slower for dyes containing multiple carboxylic acid anchors compared to single acid anchors.

A series of thienopyrazine-based donor–acceptor–donor (D–A–D) near-infrared (NIR) fluorescent compounds were synthesized through a rapid, palladium-catalyzed C–H activation route. The dyes were studied through computational analysis, electrochemical properties analysis, and characterization of their photophysical properties. Large Stokes shifts of approximately 175 nm were observed, which led to near-infrared emission. Computational evaluation shows that the origin of this large Stokes shift is a significant molecular reorganization particularly about the D–A bond. The series exhibits quantum yields of up to φ = >4%, with emission maxima ranging from 725 to 820 nm. The emission is strong in solution, in thin films, and also in isolation at the single-molecule level. Their stable emission at the single-molecule level makes these compounds good candidates for single-molecule photon sources in the near-infrared.

Treatment of 1,3-bis(3′-butylimidazolyl-1′-yl)benzene diiodide with elemental sulfur in the presence of a base produced a bis(N-heterocyclic thione) (NHT) pincer ligand precursor. Its reaction with PdCl2(CH3CN)2 produced chloro[1,3-bis(3′-butylimidazole-2′-thione-κ-S)benzene-κ-C]palladium(II), a 6,6-fused ring SCS-NHT palladium pincer complex. This air stable compound is, to our knowledge, the first SCS pincer complex that utilizes N-heterocyclic thione (NHT) donor groups. The molecular structures of the ligand precursor and the palladium complex were determined by X-ray crystallography and computational studies provided insight into the interconversion between its rac and meso conformations. The photophysical properties of the complex were established, and its catalytic activity in Suzuki, Heck, and Sonogashira cross-coupling reactions was evaluated.

This undergraduate physical chemistry laboratory exercise introduces students to the study of probability distributions both experimentally and using computer simulations. Students perform the classic coin toss experiment individually and then pool all of their data together to study the effect of experimental sample size on the binomial distribution. Simulations of the coin toss experiment are also performed using the software package LabVIEW. LabVIEW facilitates the creation of complex computer programs in a short period of time, even by beginner programmers. Histograms in LabVIEW are displayed in real time with students adjusting the number of simulated coin tosses on the fly using a virtual knob or a slider, up to 1 million individual trials. This allows the students to see firsthand the evolution of the binomial distribution into the Gaussian distribution with a large sample size.

Perylenediimide-functionalized silsesquioxane nanostructures were prepared from base-catalyzed polymerization of their respective monoalkoxysilane precursor. The shapes of nanostructures varied from nanoribbons to nanochains to nanorods upon changing the base concentration. Transmission electron microscopy confirms the twisted nature of nanoribbons with lengths up to 15 μm, whereas the dimensions of nanorods were in the range of 9 μm in length and 200 nm in width. The photovoltaic performance of the nanoribbons and nanorods were evaluated and compared for bulk heterojunction solar cells and it was discovered that morphology plays an important role in the PV performance.

This laboratory exercise introduces undergraduate chemistry majors to the spectroscopic and theoretical study of the polycyclic aromatic hydrocarbon (PAH), corannulene. Students explore the spectroscopic properties of corannulene using UV–vis and Raman vibrational spectroscopies. They compare their experimental results to simulated vibrational spectra and the molecular structure obtained from computational chemistry to other PAHs, including C60. The delocalized electron in corannulene is also conceptually explored using the particle in a disk model. This laboratory exercise allows students to explore multiple physical chemistry concepts in one, 3 h laboratory exercise centered around one theme.Keywords: Computational Chemistry; Hands-On Learning/Manipulatives; Laboratory Instruction; Nanotechnology; Physical Chemistry; Raman Spectroscopy; Upper-Division Undergraduate; UV−vis Spectroscopy;

The effects of the formation of hydrogen-bonded networks on the important osmolyte trimethylamine N-oxide (TMAO) are explored in a joint Raman spectroscopic and electronic structure theory study. Spectral shifts in the experimental Raman spectra of TMAO and deuterated TMAO microsolvated with water, methanol, ethanol, and ethylene glycol are compared with the results of electronic structure calculations on explicit hydrogen-bonded molecular clusters. Very good agreement between experiment and theory suggests that it is the local hydrogen-bonded geometry at TMAO’s oxygen atom that dominates the structure of the extended hydrogen-bonded networks and that TMAO’s unique stabilizing abilities are a result of the “indirect effect” model. Natural bonding orbital (NBO) calculations further reveal that hyperconjugation results in vibrational blue shifts in TMAO’s C–H stretching region when solvated and a red shift in methanol’s C–H stretching region when hydrogen bonding with TMAO.

The stabilization of the pyrimidine anion by the addition of water molecules is studied experimentally using photoelectron spectroscopy of mass-selected hydrated pyrimidine clusters and computationally using quantum-mechanical electronic structure theory. Although the pyrimidine molecular anion is not observed experimentally, the addition of a single water molecule is sufficient to impart a positive electron affinity. The sequential hydration data have been used to extrapolate to −0.22 eV for the electron affinity of neutral pyrimidine, which agrees very well with previous observations. These results for pyrimidine are consistent with previous studies of the hydrated cluster anions of uridine, cytidine, thymine, adenine, uracil, and naphthalene. This commonality suggests a universal effect of sequential hydration on the electron affinity of similar molecules.

Poly(3-hexylthiophene)-functionalized siloxane nanoparticles were prepared by a modified Stöber method. The photovoltaic performance of P3HT-nanohybrids with C60 derivative PCBM was evaluated. The device made from 1:1 blends of P3HT-NPs:PCBM showed reasonably good photovoltaic performance with a power conversion efficiency of 2.5% under standard test conditions (AM 1.5G, 100 mW cm−2).

A comprehensive Raman spectroscopic/electronic structure study of hydrogen bonding by pyrimidine with eight different polar solvents is presented. Raman spectra of binary mixtures of pyrimidine with methanol and ethylene glycol are reported, and shifts in ν1, ν3, ν6a, ν6b, ν8a, ν8b, ν9a, ν15, ν16a, and ν16b are compared to earlier results obtained for water. Large shifts to higher vibrational energy, often referred to as blue shifts, are observed for ν1, ν6b, and ν8b (by as much as 14 cm–1). While gradual blue shifts with increasing hydrogen bond donor concentration are observed for ν6b and ν8b, ν1 exhibits three distinct spectral components whose relative intensities vary with concentration. The blue shift of ν1 is further examined in binary mixtures of pyrimidine with acetic acid, thioglycol, phenylmethanol, hexylamine, and acetonitrile. Electronic structure computations for more than 100 microsolvated structures reveal a significant dependence of the magnitude of the ν1 blue shift on the local microsolvation geometry. Results from natural bond orbital (NBO) calculations also reveal a strong correlation between charge transfer and blue shifting of pyrimidine’s normal modes. Although charge transfer has previously been linked to blue shifting of the X–H stretching frequency in hydrogen bond donors, here, a similar trend in a hydrogen bond acceptor is demonstrated.

Perylenediimide functionalized bridged siloxane nanoparticles were prepared by direct hydrolysis and condensation of a perylenediimide silane precursor in the presence of a catalytic amount of tetraethoxysilane (TEOS). The sizes of the particles were controlled by adjusting organotrialkoxysilane, base, and TEOS concentrations. Using this modified Stöber method, we were able to incorporate a higher load of organic content (∼70%) into the siloxane core compared to typical organically modified Stöber silica nanoparticles. The size, shape, and surface morphology of these functionalized particles were visualized using transmission electron microscopy. Their compositions were confirmed by FTIR, thermogravimetric analysis, and elemental analysis. The photovoltaic performance of these nanohybrids in the poly(3-hexylthiophene) polymer matrix was evaluated. The device made from a sample annealed at 150 °C showed reasonably good photovoltaic performance with a power conversion efficiency of 1.56% under standard test conditions of AM 1.5G spectra at an illumination intensity of 100 mW cm−2.

The recently reported metalation/transmetalation route for the synthesis of CCC-bis(NHC) pincer ligand supported transition-metal complexes was extended to Pt. 2-(1,3-Bis(N-butylimidazol-2-ylidene)phenylene)(chloro)platinum(II) (1) and its bromo analogue 2 were synthesized and characterized. X-ray crystal structure determinations revealed complexes 1 and 2 to have distorted-square-planar configurations around the metal. Photophysical and thermal properties of these complexes are reported, and their extended photostability in air is discussed and contrasted. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations of the ground state and various low-lying excited states have revealed admixing of Pt 5d orbitals and the ligand π* orbitals for both the ground state and the low-lying excited states of complex 1, indicating the low-lying states to be a mixture of metal-to-ligand charge-transfer and ligand-centered transition (MLCT-LC). Somewhat surprisingly, the computed gas-phase geometry of the excited state of complex 1 had a significant distortion, mostly about the Caryl–Pt–Cl angle. These complexes were congeners of materials for organic light emitting diodes (OLEDs).

The physical chemistry laboratory is sometimes constrained to one semester, resulting in pedagogical deficiencies for the students taking the course. The use of a multidimensional laboratory exercise offers students the opportunity to encounter multiple experimental techniques and physical chemistry concepts while not sacrificing a significant amount of time. Here, we show that the classic binary liquid–vapor phase diagram experiment can be modified to incorporate both molecular spectroscopy and quantum chemistry. Using Raman spectroscopy as a means of detection and quantum chemistry to investigate the resulting vibrational spectra, students can explore three important subject areas in one laboratory exercise.Keywords: Computational Chemistry; Hands-On Learning/Manipulatives; Laboratory Instruction; Phases/Phase Transitions/Diagrams; Physical Chemistry; Quantum Chemistry; Raman Spectroscopy; Upper-Division Undergraduate;

N-Methyliminodiacetic acid (MIDA)-protected boronate esters are a new class of reagents that offer great promise in iterative Suzuki-Miyaura cross-coupling reactions. Compared to earlier reagents, MIDA esters are easily handled and are benchtop stable under air indefinitely. The success of this new species is tied to its unique molecular architecture. Compared to the simpler B–N containing molecules ammonia borane and trimethylamine borane, MIDA esters are much larger, and the sp3 hybridized boron atom is secured by two five membered rings, making this molecular class stable for spectroscopic study. Here, we present infrared, Raman, and surface enhanced Raman (SERS) spectra of methylboronic acid MIDA ester. Comparisons of the spectroscopic results to those from electronic structure calculations suggest that the B–N stretching mode in this molecule lies in the range 560–650 cm–1, making it among the lowest energy vibrations observed to date that can be primarily attributed to B–N stretching.

The effects of hydration on vibrational normal modes of trimethylamine N-oxide (TMAO) are investigated by Raman spectroscopy and electronic structure computations. Microsolvated networks of water are observed to induce either red or blue shifts in the normal modes of TMAO with increasing water concentration and to also exhibit distinct spectral signatures. By taking advantage of the selective and gradual nature of the water-induced shifts and using comparisons to theoretical predictions, the assignments of TMAO’s normal modes are re-examined and the structure of the hydrogen-bonded network in the vicinity of TMAO is elucidated. Agreement between experiment and theory suggests that the oxygen atom in TMAO accepts on average at least three hydrogen bonds from neighboring water molecules and that water molecules are likely not directly interacting with TMAO’s methyl groups.

The effects of weak intermolecular interactions on 10 vibrational normal modes of pyrimidine are investigated by Raman spectroscopy and electronic structure computations. Hydrogen-bonded networks of water induce a shift to higher energy in certain normal modes of pyrimidine with increasing water concentration, while other modes are relatively unaffected. Pyrimidine molecules also exhibit weak C−H···N interactions and shifted normal modes upon crystallization. The selective nature of the shifting of normal modes to higher energy allows for definitive assignments of the nearly degenerate ν8a and ν8b modes with polarized Raman spectroscopy. Natural bond orbital (NBO) analyses indicate that when water molecules donate hydrogen bonds to the nitrogen atoms of pyrimidine, there is significant charge transfer from pyrimidine to water, much of which can be accounted for by substantial decreases in the populations of the nitrogen lone pair orbitals. Despite the overall decrease of electron density in pyrimidine upon complexation with water, there are concomitant changes in NBO populations that polarize the π-electron system toward the proton acceptor N atoms, as well as contractions of the bonds associated with the N−C−N and C−C−C regions of the pyrimidine ring.

CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures.

Treatment of 1,3-bis(3′-butylimidazolyl-1′-yl)benzene diiodide with elemental sulfur in the presence of a base produced a bis(N-heterocyclic thione) (NHT) pincer ligand precursor. Its reaction with PdCl2(CH3CN)2 produced chloro[1,3-bis(3′-butylimidazole-2′-thione-κ-S)benzene-κ-C]palladium(II), a 6,6-fused ring SCS-NHT palladium pincer complex. This air stable compound is, to our knowledge, the first SCS pincer complex that utilizes N-heterocyclic thione (NHT) donor groups. The molecular structures of the ligand precursor and the palladium complex were determined by X-ray crystallography and computational studies provided insight into the interconversion between its rac and meso conformations. The photophysical properties of the complex were established, and its catalytic activity in Suzuki, Heck, and Sonogashira cross-coupling reactions was evaluated.