Spectra and photophysics of new organic fluorophores: 2,3-Di(phenylethenyl)benzofuran derivatives

Conformations, spectra and photophysics of a series of new organic fluorophores, 2,3-distyrylbenzofuran derivatives, have been studied by a combined theoretical and experimental approach. Ground electronic state geometries have been investigated by Hartree-Fock ab initio methods and Density Functional Theory. Electronic spectra have been calculated with the CS INDO S-CI and SDT-CI procedures. Spectral and photophysical behaviour has been investigated by stationary and time-resolved techniques. Solvatochromism of these compounds has been analyzed. The UV-vis absorption spectra of the substituted compounds are very similar, showing a red shift in the series H < Cl < OCH3 < NH2 < NO2. The CS INDO CI analysis of the electronic spectra of all rotamers shows coherence with the prevalent presence of one non-planar conformer. These compounds are very stable and show an intense and structured fluorescence indicating that the emitting state is the same as that reached by absorption, i.e. the |πHπL∗〉 singlet state. The nitro-derivative behaviour is exceptional if compared to the other compounds since it displays a strong fluorosolvatochromism, due to an intramolecular charge transfer state.