Solvent Effects on the Phosphorescence of Gold(III) Complexes Chelated by β-Multisubstituted Corroles.

Abstract

A set of gold corrole complexes containing four different β-substituent groups (Br/I/CF3), namely, 4Br-Au, 4I-Au, and 4CF3-Au, were investigated; all showed room temperature phosphorescence. The phosphorescence quantum yields of the corroles were determined using tetraphenylporphyrin as a reference: Φph (4I-Au, 0.75%) > Φph (4Br-Au, 0.64%) > Φph (4CF3-Au, 0.38%). 4CF3-Au exhibited near-IR emission (858 nm, aerobic); absorbance intensity for the Q-band was higher than that for the Soret band. Complex 4I-Au showed a longer phosphorescence lifetime (82 μs) compared to those of 4Br-Au (53 μs) and 4CF3-Au (28 μs; N2, tol). Thermally activated delayed fluorescence (TADF) emission of 4I/Br-Au complexes was observed: stronger emission intensity correlated with increasing temperature. Good negative correlations for 4I/Br-Au were observed between the Soret band absorption energy and the solvent polarizability: excited states of 4I/Br-Au are more polar than their ground states. TD-DFT calculations revealed very fast intersystem crossing (ISC) rate constants, 2.20 × 1012 s-1 (4CF3-Au) > 1.96 × 1011 s-1 (4Br-Au) > 1.15 × 1011 s-1 (4I-Au), and importantly, the reverse intersystem crossing (rISC) rate constants are determined as 1.68 × 107 s-1 (4I-Au) > 2.40 × 103 s-1 (4Br-Au) ≫ 8.09 × 10-8 s-1 (4CF3-Au). The exceptionally low rISC rate constant of 4CF3-Au is attributed to its more steric and deformed structure bearing a larger energy gap between the S1 and T1 states.