Transfer of Vibrational Energy in Dye-Doped Polymers

Johannes Baier, Thomas Dahinten, and Alois Seihneier 

Photoexcitation or radiationless relaxation processes supply a lot of thermal excess energy to polymer systems. In particular, dye molecules dispersed in polymers reach transient excess temperatures of several 100 K by absorbing visible light [1], The equilibration of the excess energy is of interest in the discussion of the photostabUity and of the kinetics of polymer dye interaction [2] of such systems. In the condensed phases the energy relaxation is determined by microscopic transfer processes proceeding on a picosecond time scale. 

In recent years many investigations have been performed on intra and intermolecular energy transfer in the gas phase and in liquids. Whereas in low-pressure gases time constants extending to the microsecond range have been reported, transfer times from a fraction of a picosecond to several picoseconds are observed in the liquid state [3]. There the considerably higher density results in larger collision frequencies and shorter relaxation times. 

In this paper, the transfer of vibrational energy in polymers doped with dye molecules is investigated. Similar experiments have been already discussed after exciting C-H stretching modes aroimd v = 3000 cm [4]. Here we present data for the first time where the more important skeletal modes between v = 1500 cm and v = 1800 cm are pumped. Two types of experiments are discussed  

The experimental data are taken on polycarbonate doped with the dye coumarin 6. 

---