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

Abstract

A set of gold corrole complexes containing four different beta-substituent groups (Br/I/CF3), namely, 4Br-Au, 4I-Au, and 4CF(3)-Au, were investigated; all showed room temperature phosphorescence. The phosphorescence quantum yields of the corroles were determined using tetraphenylporphyrin as a reference: Phi(ph) (4I-Au, 0.75%) > Phi(ph) (4Br-Au, 0.64%) > Phi(ph) (4CF(3)-Au, 0.38%). 4CF(3)-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 mu s) compared to those of 4Br-Au (53 mu s) and 4CF(3)-Au (28 mu s; 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 x 10(12) s(-1) (4CF3-Au) > 1.96 x 10(11) s(-1) (4BrAu) > 1.15 x 10(11) s(-1) (4I-Au), and importantly, the reverse intersystem crossing (rISC) rate constants are determined as 1.68 x 10(7) s(-1) (4I-Au) > 2.40 x 10(3) s(-1) (4Br-Au) >> 8.09 x 10(-8) s(-1) (4CF(3)-Au). The exceptionally low rISC rate constant of 4CF(3)-Au is attributed to its more steric and deformed structure bearing a larger energy gap between the S-1 and T-1 states.