Photophysical properties of the triangular [Au(HNCOH)]3 complex and its dimer

Abstract

Rate constants for radiative and non-radiative transitions of the [Au(HNCOH)]₃ complex and its dimer were calculated within the Herzberg–Teller approximation based on quantum mechanical principles. A high triplet quantum yield was estimated for the monomer. Internal conversion (IC) was found to be the major competing process to the intersystem crossing (ISC) from the lowest excited singlet state (S₁) to the lowest triplet state (T₁). ISC and IC from the spin-mixed ₁ state also dominate the triplet relaxation process resulting in a negligible phosphorescence quantum yield for the monomer. The IC and ISC rate constants of the dimer are considerably smaller due to much lower Franck–Condon factors. For the dimer a triplet quantum yield of 0.71 was estimated using the extended multi-configuration quasi-degenerate second-order perturbation theory (XMCQDPT2) method to calculate the transition energies. Fluorescence is the major competing process to the ISC relaxation of the S₁ state of the dimer. The ISC and IC processes are insignificant for the relaxation of the T₁ state, resulting in unity phosphorescence quantum yield. The high triplet and phosphorescence quantum yields of the [Au(HNCOH)]₃ dimer make it and its higher oligomers potential candidates as dopants for phosphorescent organic light emitting diodes and as down-converters in solid-state lighting systems.