Photophysical Heavy-Atom Effect in Iodinated Metallocorroles: Spin-Orbit Coupling and Density of States

0494128 - ÚFCH JH 2019 RIV US eng J - Journal Article
Pomarico, E. - Pospíšil, Petr - Bouduban, M. E. F. - Vestfrid, J. - Gross, Z. - Záliš, Stanislav - Chergui, M. - Vlček, Antonín
Photophysical Heavy-Atom Effect in Iodinated Metallocorroles: Spin-Orbit Coupling and Density of States.
Journal of Physical Chemistry A. Roč. 122, č. 37 (2018), s. 7256-7266. ISSN 1089-5639. E-ISSN 1520-5215
R&D Projects: GA ČR GA17-01137S
Grant - others:COST(XE) CM1405
Institutional support: RVO:61388955
Keywords : Aluminum compounds * Charge transfer * Chromophores
OECD category: Physical chemistry
Impact factor: 2.641, year: 2018

Excited-state dynamics and electronic structures of Al and Ga corrole complexes were studied as a function of the number of β-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(Ï€) participation in the corrole Ï€-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 Ï€-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.
Permanent Link: http://hdl.handle.net/11104/0287388