RAPID MIGRATION AND TRAPPING OF PHOTOEXCITED ELECTRONIC-ENERGY IN AMPHIPHILIC POLYELECTROLYTES CONTAINING NAPHTHALENE CHROMOPHORES AND PYRENE TRAPS

Electronic energy migration and transfer from naphthalene (Np) chromophores to pyrene (Py) traps covalently incorporated in terpolymers of sodium 2-acrylamido-2-methylpropanesulfonate, N-(1-naphthylmethyl)methacrylamide, and N-(1-pyrenylmethyl)methacrylamide were investigated. Very efficient energy transfer from Np to Py occurred at room temperature in aqueous solution where the terpolymers form a microphase-separated structure consisting of chromophore clusters. For a terpolymer containing a 59 mol % Np chromophore and a 1 mol % Py trap, the efficiency of singlet energy transfer (chi) in aqueous solution was estimated to be practically unity. The terpolymer showed a rapid decay of Np fluorescence with a decay constant of 19 ps and a corresponding rapid rise of Py fluoresence with a rise time of 20 ps on excitation of the Np chromophores at 290 nm. These observations imply that extremely fast migration of singlet energy between the Np chromophores and transfer to the Py traps occur in the chromophore cluster of the terpolymer in aqueous solution. This work represents the most rapid and efficient energy transfer in synthetic "photon-harvesting" polymers reported so far. These remarkable photophysical characteristics may be due to the structural features of the present amphiphilic polyelectrolyte in which the chromophores are bound to the main chain through amide bonding.