Non-radiative energy transfer in polymers

Abstract

THE study of intra- and intermolecular transfer of energy by non-radiative processes is important in developing an understanding of such phenomena as photosynthesis and photo-stabilisation of polymers. Several theories have been proposed, notable among which is the dipole–dipole mechanism due to Förster¹ and Galanin². Apart from the dependence on distance separating donor and acceptor, the probability of transfer is related to the angle between donor and acceptor moments. For this reason measurements of fluorescence depolarisation can be used to estimate the efficiency of transfer from donor to acceptor. Macromolecules provide interesting potential for studying intra- as well as intermolecular non-radiative transfer. Thus chromophore-bearing polymers such as polystyrene allow the possibility of excitation at one part of the molecule, transfer along the chain from one phenyl unit to another until an energy trap, an excimer site, is reached whereupon the energy is emitted as a photon. The principal emission observed from polystyrene at room temperature is that from excimer. We wish to make a preliminary report on some studies we have made on fluorescence depolarisation using a styrene–phenyl acetylene copolymer as donor, and perylene as acceptor.