Aggregation structure of poly(γ-benzyl- l-glutamate) in benzene-DMF mixed solution probed by fluorescence depolarization and non-radiative energy transfer

Abstract

The aggregation of poly(γ-benzyl- l-glutamate) (PBLG) in mixed solution of benzene and N,N-dimethylformamide (DMF) was studied by the emission probe method. Samples of PBLG with 260 and 790 of average degree of polymerization containing anthryl group (An-PBLG260 and An-PBLG790) and carbazolyl group (Cz-PBLG260 and Cz-PBLG790) were prepared. The mean rotational relaxation times ( ρ rot) of the anthryl probe in An-PBLG260 and An-PBLG790 were evaluated in benzene(Bz)-DMF solutions. The apparent efficiencies of the non-radiative intermolecular energy transfer from the carbazolyl probe to the anthryl probe in different PBLG molecules were estimated spectroscopically in Bz-DMF solutions. In benzene solution, ρ rot for An-PBLG260 is larger than that for An-PBLG790 and the efficiency of the energy transfer for PBLG260 is larger than that for PBLG790. With increase in DMF content in Bz-DMF mixtures, ρ rot decreases up to 15% DMF content and the efficiencies of energy transfer decrease for PBLG260 and PBLG790. These results show that the extent of an anti-parallel aggregation of PBLG260 in benzene is larger than that of PBLG790 and that the mobility of the anthryl probe in PBLG260 is smaller than that in PBLG790 in the aggregated state.