Photophysical Heavy-Atom Effect in Iodinated Metallocorroles: Spin-Orbit Coupling and Density of States
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 conco...
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| Vydáno v: | The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Ročník 122; číslo 37; s. 7256 |
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| Hlavní autoři: | , , , , , , , |
| Médium: | Journal Article |
| Jazyk: | angličtina |
| Vydáno: |
United States
20.09.2018
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| ISSN: | 1520-5215, 1520-5215 |
| On-line přístup: | Zjistit podrobnosti o přístupu |
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| Shrnutí: | 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(π) participation in the corrole π-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 π-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. |
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| Bibliografie: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 1520-5215 1520-5215 |
| DOI: | 10.1021/acs.jpca.8b05311 |