Fluorescence quenching by intermolecular π-π interactions of 2,5-bis(N,N-dialkylamino)-3,6-dicyanopyrazines

The fluorescence properties of 2,5-bis(N,N-dialkylamino)-3,6-dicyanopyrazine dyes in the solid state were correlated with their molecular stacking behavior. The optimized molecular structures were evaluated by using MOPAC PM3 and AM I methods and their stacking behaviors of the pi-chromophoric system were simulated from their three dimensional molecular structures and H-1 NMR spectra. The steric requirements of the substituents in the parent chromophoric system were the main cause of the spectral changes in the absorption and fluorescence maxima and fluorescence intensity in the solid state. Intermolecular pi-pi interactions effectively quenched the solid state fluorescence and, consequently, the degree of fluorescence quenching can be used as an indicator of intermolecular pi-pi interactions of fluorescence dyes chromophores. (C) 1999 Elsevier Science Ltd. All rights reserved.