Computational analyses of singlet-singlet and singlet-triplet transitions in mononuclear gold-capped carbon-rich conjugated complexes

Abstract

Density functional theory and CASSCF calculations have been used to determine equilibrium geometries and vibrational frequencies of metal-capped one-dimensional pi-conjugated complexes (H3P)Au(C equivalent to C)(n)(Ph) (n = 1-6), H3P-Au(C equivalent to CC6H4)(C equivalent to CPh) and H3P-Au(C equivalent to CC6H4)C equivalent to CAu-PH3 in their ground states and selected low-lying pi pi* excited states. Vertical excitation energies for spin-allowed singlet-singlet and spin-forbidden single-triplet transitions determined by the time-dependent density functional theory show good agreement with available experimental observations. Calculations indicate that the lowest energy (3)(pi pi*) excited state is unlikely populated by the direct electronic excitation, while the low-lying singlet and triplet states, slightly higher in energy than the lowest triplet state, are easily accessible by the excitation light used in experiments. A series of radiationless transitions among related excited states yield the lowest (3)(pi pi*) state, which has enough long lifetimes to exhibit its pholochemical reactivities, (c) 2005 Wiley Periodicals, Inc.