Correlation of molecular vibrational structure with luminescent quantum yields

The luminescent quantum yield of organic materials is strongly determined by both their molecular structure and that of their local environment. The effect of the latter is illustrated for the case of the model compounds terphenyl and a phenylene-vinylene trimer in a range of organic solvents. Although weak solvatochromic shifts of the absorption and luminescence spectra are observable, they do not account for the dramatic variation in luminescent quantum yields. The large variation in the luminescent output suggests that the quantum yields are dictated by nonradiative processes. Raman spectroscopy is employed to examine the correlation of the vibrational structure of the chromophore with that of its local environment. The luminescent output of the solution is observed to scale linearly with this vibrational overlap. To date, similar studies in even dilute solutions of the para-meta-phenylene vinylene copolymer PmpPV have shown a predominance of aggregation effects. The implications on the prospect of controlling the quantum yields of organic materials in the solid state are discussed.