Correlation between Photophysical Parameters and Gold–Gold Distances in Gold(I) (4-Pyridyl)ethynyl Complexes

The systematic analysis of the luminescence of a series of alkynyl gold derivatives with general formulas [(diphos)(AuC≡Cpy)(2)] (diphosphane =2,2'-bis(diphenylphosphanyl)propane or dppip (1), bis(diphenylphosphanyl)acetylene or dppa (2), 1,2-bis(diphenylphosphanyl)ethane or dppe (3) and 1,4-bis(diphenylphosphanyl)butane or dppb, (4), has shown a straightforward correlation between the Au(I)···Au(I) distance and the emission quantum yields and decaytimes. The analysis of the decaytimes, quantum yields and thus, the corresponding calculated rate constants demonstrated the existence of a correlation between Au(I)···Au(I) distance and the radiative rate constant for the deactivation of the emissive triplet states. It was concluded that the increased emission of these compounds results from the increase in spin-orbit coupling that favors the spin forbidden transition to the singlet ground state.