Indexed by:Journal Papers

Date of Publication:2020-02-20

Journal:JOURNAL OF PHYSICAL CHEMISTRY C

Included Journals:SCIE

Volume:124

Issue:7

Page Number:3939-3951

ISSN No.:1932-7447

Abstract:The orthogonal boron dipyrromethene (BODIPY) dimers, showing efficient spin-orbit charge transfer intersystem crossing (SOCT ISC) as promising photosensitizers for photodynamic therapy, are studied intensively with time-resolved electron paramagnetic resonance spectroscopy (TREPR). The spectral and kinetic properties of the charge recombination-induced triplet states of two BODIPY dyads have been explored by TREPR spectroscopy. The experimental data are consistent with the formation of the initial electron spin polarization by a SOCT ISC mechanism. However, the comparison of the relative populations of the triplet states shows that some other ISC channel can also be involved. The balance of the excited triplet states localized on either part of the dyads has been proved, and the intramolecular energy transfer between two parts in a dyad has been established. The absolute population rates of the sublevels of the triplet state were determined. Two BODIPY dimers have different spin-lattice relaxation (SLR) times. For one of the dimers, SLR is highly anisotropic (slower at the canonical orientations). The anisotropic SLR is attributed to the fast reversible intramolecular energy transfer between two subunits in the dimer with different orientations of the ZFS principal axes. The developed model of the spin evolution rationalizes all observed properties and provides a quantitative description of the time/magnetic field data sets.