Dual fluorescence of 2-(4 '-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole: effect of solvents

Spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)pyrido[3,Cd]imida zole (DMAPPI) have been studied in different solvents. Dual fluorescence is observed in polar/aprotic and polar/protic solvents. Short wavelength (SW) emission band is assigned to the locally excited (B*) state, whereas the l ong wavelength (LW) emission band is due to the twisted intramolecular char ge transfer (TICT, A*) state. Fluorescence excitation spectra recorded at S W and LW emissions suggest that both these emission originate from the same ground state species. Time correlated fluorescence studies have suggested that there is no equilibrium between these emissions in the excited state. The reverse reaction of TICT state to the B* state is much slower than the forward reaction of B* state to A* state. AM1 calculations were carried out on the isolated and solvated DMAPPI molecules. These studies have shown th at the hydrogen bonding made the pyridoimidazole (PI) ring more planar with benzene ring and this facilitates the flow of charge from the N,N-dimethyl aminophenyl (DMAP) ring to the electron withdrawing group (PI). (C) 1999 El sevier Science B.V. All rights reserved.