Correlation of molecular vibrational structure with luminescent quantum yields

The luminescent quantum yield of organic materials is strongly determined b y both their molecular structure and that of their local environment. The e ffect of the latter is illustrated for the case of the model compounds terp henyl and a phenylene-vinylene trimer in a range of organic solvents. Altho ugh weak solvatochromic shifts of the absorption and luminescence spectra a re observable, they do nor account for the dramatic variation in luminescen t quantum yields. The large variation in the luminescent output suggests th at the quantum yields are dictated by nonradiative processes. Raman spectro scopy is employed to examine the correlation of the vibrational structure o f the chromophore with that of its local environment. The luminescent outpu t of the solution is observed to scale linearly with this vibrational overl ap. To date, similar studies in even dilute solutions of the para-meta-phen ylene vinylene copolymer PmpPV have shown a predominance of aggregation eff ects. The implications on the prospect of controlling the quantum yields of organic materials in the solid state are discussed. (C) 2000 Elsevier Scie nce S.A. All rights reserved.