Theoretical analysis of photosensitization of DNA by thionine.

Context: In this work, we are the first to perform a theoretical analysis of photoinduced charge transfer in the intercalation complex of thionine (TH) with double-stranded DNA, which was observed in experiments. Efficient DNA binding and long-wave absorption maximum make TH an attractive photosensitizer. d(CpG) tetranucleotide was used as a minimal model DNA fragment.

TD-DFT analysis of excitation of the closed-form spironaphthopyran in methanol solution: The contribution of vibronic transitions and intermolecular hydrogen bonds.

A set of forty hybrid functionals, combined with a 6-31++G(d,p) basis set and an IEFPCM solvent description, was applied to calculate the S→S excitation of the spironaphthopyran (SNP) photochromic compound. None of the hybrid functionals resulted in C-O bond cleavage upon optimization of the S excited state of the SNP, in contrast to the spiropyran BIPS which we studied earlier. At the same time, the deformations of the SNP during excitation turned out to be very small (in contrast to those for BIPS) which made it possible to calculate its vibronic absorption spectrum.

Intramolecular excimers of open forms of 2-benzopyran, 2- and 3-naphthopyrans in solution: TD-DFT/DFT analysis.

We hypothesized that in the open forms of diphenyl-substituted photochromic compounds, immediately after the photoinduced cleavage of the C-O bond, one of the phenyl rings forms a stack with an aromatic system at the other end of the alkyl linker. The formation of these intramolecular stacking excimers is made possible by a known increase in the rotational mobility of the linker double bonds in the excited state. The flexibilities of linkers are analyzed in terms of changes in their dihedral angles.

4a,4b-Dihydrophenanthrene → cis-stilbene photoconversion: TD-DFT/DFT study.

Context: DHP → CS photoconversion was analyzed in terms of electron density redistribution for the first time. The following explanation for the non-recovery of the C4a-C4b bond upon CS relaxation is proposed: during this process, the Coulomb repulsion energy between these pairs of atoms increases by almost one and a half times, and their bonding by an electron at LUMO is insufficient to recover the C4a-C4b bond. According to calculations, upon CS relaxation, the linker connecting the benzene rings undergoes significant structural changes.

TD-DFT study of BIPS spiropyran: Effects of functionals and high-polarity solvent on C O bond dissociation and recovery.

We performed a theoretical analysis of the BIPS photochemical cycle using an extensive set of forty hybrid functionals and taking into account a highly polar solvent (methanol). The functionals with a small fraction of the exact Hartree-Fock exchange (%HF) showed the predominant S  → S transition with the strengthening of the C O bond. At the same time, functionals with medium and high %HF (including those with long-range correction) gave a dominant S  → S transition with weakening or breaking of the C O bond, which corresponds to the experimental results.