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, <b>4Br-Au</b>, <b>4I-Au</b>, and <b>4CF</b>_<b>3</b><b>-Au</b>, were investigated; all showed room temperature phosphorescence. The phosphorescence quantum yields of the corroles were determined using tetraphenylporphyrin as a reference: Φ_ph (<b>4I-Au</b>, 0.75%) > Φ_ph (<b>4Br-Au</b>, 0.64%) > Φ_ph (<b>4CF</b>_<b>3</b><b>-Au</b>, 0.38%). <b>4CF</b>_<b>3</b><b>-Au</b> exhibited near-IR emission (858 nm, aerobic); absorbance intensity for the Q-band was higher than that for the Soret band. Complex <b>4I-Au</b> showed a longer phosphorescence lifetime (82 μs) compared to those of <b>4Br-Au</b> (53 μs) and <b>4CF</b>_<b>3</b><b>-Au</b> (28 μs; N₂, tol). Thermally activated delayed fluorescence (TADF) emission of <b>4I/Br-Au</b> complexes was observed: stronger emission intensity correlated with increasing temperature. Good negative correlations for <b>4I/Br-Au</b> were observed between the Soret band absorption energy and the solvent polarizability: excited states of <b>4I/Br-Au</b> are more polar than their ground states. TD-DFT calculations revealed very fast intersystem crossing (ISC) rate constants, 2.20 × 10¹² s^-1 (<b>4CF</b>_<b>3</b><b>-Au</b>) > 1.96 × 10¹¹ s^-1 (<b>4Br-Au</b>) > 1.15 × 10¹¹ s^-1 (<b>4I-Au</b>), and importantly, the reverse intersystem crossing (rISC) rate constants are determined as 1.68 × 10⁷ s^-1 (<b>4I-Au</b>) > 2.40 × 10³ s^-1 (<b>4Br-Au</b>) ≫ 8.09 × 10^-8 s^-1 (<b>4CF</b>_<b>3</b><b>-Au</b>). The exceptionally low rISC rate constant of <b>4CF</b>_<b>3</b><b>-Au</b> is attributed to its more steric and deformed structure bearing a larger energy gap between the S₁ and T₁ states.