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 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 in...