A group of nonyl acridine orange analogues (NAO) was prepared which were designed to have the potential of possessing visible bands allowing them to act in cells as fluorescence resonance energy transfer (FRET) donors with the photodynamic therapy drug Pc 4. The existence of Pc 4-FRET with the analogues of NAO in MCF-7c3 cells was probed. The results suggest that NAO analogues giving strong FRET with Pc 4 in cells can be found.

•Synthesis of a novel silicon phthalocyanine, Pc 61.•Investigation of the relation between dye loading and performance of the DSSC.•Measurements of injection rates of Pc 61-based DSSC as function of dye adsorption.•Solar cells fabricated with an optimized dye immersion time.•Measured the sensitizer excited state dynamics via laser spectroscopy.Silicon phthalocyanines with bulky axial ligands are interesting materials for dye-sensitized solar cells (DSSCs) because they possess a strong absorption in the red region (~670 nm) and their ligands hinder the stacking of their rings. This suppresses the formation of aggregates, a common tendency of dyes on the surface of dye-sensitized metal-oxide layers. Herein, the novel silicon phthalocyanine, Pc 61, which has ligands terminating in carboxylic acid groups has been synthesized, characterized and used in studies on the harnessing of photons in the long-wavelength visible light range. To investigate the relation between dye loading and performance of DSSCs, a series of Pc 61-sensitized TiO2 films and DSSC devices with different dye immersion times have been prepared and characterized through optical, electrical and laser spectroscopic studies. To our knowledge, this is the first time that injection rates of phthalocyanine-based DSSC performance have been assessed as a function of dye immersion time. The results of the incident photocurrent conversion efficiency (IPCE) and power conversion efficiency (ηeff) studies reveal that solar cells fabricated with a 120 min Pc 61 immersion time have the best performance among the tested ones. This is corroborated by time-resolved emission lifetime data. Our studies demonstrate that the short photoluminescence lifetime of Pc 61–TiO2 films results from efficient electron injection by excited-state Pc 61 into the TiO2 film. This agreed with both experimentally obtained higher IPCE and higher ηeff.

The photosensitive, alkyl- and alkylsiloxy-ligated silicon phthalocyanine, SiPc[(CH2)3SH][OSi(CH3)2(CH2)3N(CH3)2], Pc 227, has been prepared and characterized. This phthalocyanine yields the experimental photodynamic therapy (PDT) drug Pc 4, SiPc[OH][OSi(CH3)2(CH2)3N(CH3)2], when irradiated with red light. To provide an understanding of the process by which Pc 227 and other alkyl-alkylsiloxysilicon phthalocyanines such as Pc 227 are photolyzed, bond dissociation energy, natural bond orbital (NBO) charge distribution, spin density distribution, nucleus-independent chemical shift (NICS), and electron localization function (ELF) calculations have been carried out on two models related to it. These show that the lowest energy pathway for the photolysis of Pc 227 is a homolysis involving a phthalocyanine π radical having a low SiPc–C bond dissociation energy. The promise of the results of this study for synthetic chemistry and drug development is discussed.

Crystal structures have been determined for the three-member set of cofacial silicon phthalocyanines, ((n-C6H13)3SiO)[SiPcO]1–3(Si(n-C6H13)3). The staggering angles between adjacent rings in the dimer and trimer of this set are ∼16°. The interactions leading to these angles have been investigated by the atoms-in-molecules (AIM) and reduced-density-gradient (RDG) methods. The results show that long directional interactions (LDIs) are responsible for these angles. A survey of the staggering angles in various cofacial phthalocyanines described in the literature has revealed the existence of significant LDIs in a number of them. It is apparent that in many cases the ability of LDIs to dominate the forces giving rise to the staggering angles observed in cofacial phthalocyanines depends on their inter-ring separations.

Single crystal structures have been determined for the three cofacial, oxygen-bridged, silicon phthalocyanine oligomers, [((CH3)3SiO)2(CH3)SiO](SiPcO)2–4[Si(CH3)(OSi(CH3)3)2], and for the corresponding monomer. The data for the oligomers give structural parameters for a matching set of three cofacial, oxygen-bridged silicon phthalocyanine oligomers for the first time. The staggering angles between the six adjacent cofacial ring pairs in the three oligomers are not in a random distribution nor in a cluster at the intuitively expected angle of 45° but rather are in two clusters, one at an angle of 15° and the other at an angle of 41°. These two clusters lead to the conclusion that long, directional interactions (LDI) exist between the adjacent ring pairs. An understanding of these interactions is provided by atoms-in-molecules (AIM) and reduced-density-gradient (RDG) studies. A survey of the staggering angles in other single-atom-bridged, cofacial phthalocyanine oligomers provides further evidence for the existence of LDI between cofacial phthalocyanine ring pairs in single-atom-bridged phthalocyanine oligomers.

In this feature article, gold nanoparticle conjugates loaded with phthalocyanine-based PDT drugs are prepared and tested for delivery efficiency and PDT efficacy on HeLa cancer cells. It could be shown that the delivery and PDT outcome are strongly affected by the bond that links the drug load to the nanoparticle surface. Whereas labile amino adsorption to the Au nanoparticle surface allows for efficient drug release into the cancer cells and for efficient PDT, a covalent thiol bond to the Au nanoparticle leads to the delivery of the drug into cell vesicles, and no PDT effect is observed. This work highlights the importance of carefully choosing the interaction between drug molecules and the nanoparticle surface.