Pomarico, EnricoPospisil, PetrBouduban, Marine E. F.Vestfrid, JenyaGross, ZeevZalis, StanislavChergui, MajedVlcek, Antonin2018-12-132018-12-132018-12-132018-09-2010.1021/acs.jpca.8b05311https://infoscience.epfl.ch/handle/20.500.14299/152526WOS:000445711900002Excited-state dynamics and electronic structures of Al and Ga corrole complexes were studied as a function of the number of beta-pyrrole iodine substituents. Using spectrally broad-band femtosecond-resolved fluorescence upconversion, we determined the kinetics of the Soret fluorescence decay, the concomitant rise and subsequent decay of the Q-band fluorescence, as well as of the accompanying vibrational relaxation. Iodination was found to accelerate all involved processes. The time constant of the internal conversion from the Soret to the Q states decreases from 320-540 to 70-185 fs upon iodination. Vibrational relaxation then occurs with about 15 and 0.36-1.4 ps lifetime for iodine-free and iodinated complexes, respectively. Intersystem crossing to the lowest triplet is accelerated up to 200 times from nanoseconds to 15-24 ps; its rate correlates with the iodine p(pi) participation in the corrole pi-system and the spin-orbit coupling (SOC) strength. TDDFT calculations with explicit SOC show that iodination introduces a manifold of low-lying singlet and triplet iodine -> corrole charge-transfer (CT) states. These states affect the photophysics by (i) providing a relaxation cascade for the Soret -> Q internal conversion and cooling and (ii) opening new SOC pathways whereby CT triplet character is admixed into both Q-singlet excited states. In addition, SOC between the higher Q singlet and the Soret triplet is enhanced as the iodine participation in frontier corrole pi-orbitals increases. Our observations that iodination of the chromophore periphery affects the whole photocycle by changing the electronic structure, spin-orbit coupling, and the density of states rationalize the "heavy-atom effect" and have implications for controlling excited-state dynamics in a range of triplet photosensitizers.Chemistry, PhysicalPhysics, Atomic, Molecular & ChemicalChemistryPhysicsfree-base corrolessoret-excited tetrapyrrolesfemtosecond fluorescencetriplet photosensitizersgallium corrolescobalt corroleup-conversiondynamicsaluminumcomplexestext::journal::journal article::research article