Theoretical investigation of two-photon absorption and fluorescence properties of cypridina luciferin-based derivatives: 2,3,5-trisubstituted pyrazine compounds

Two-photon fluorescent probe materials are significant for achieving observation of living phenomena in entire organs and tissues. To explore new materials with high fluorescence and large two-photon absorption (TPA) cross section, a series of 2,3,5-trisubstituted pyrazine derivatives were designed. Their equilibrium geometries, one-photon absorption, TPA, and luminescence properties have been studied by using density functional theory (DFT), time-dependent DFT, and Zerner's intermediate neglect of differential overlap program. The results show that the introduction of styrene groups to 2,3,5-trisubstituted pyrazine derivatives can efficiently increase the conjugated effect and enhance the TPA activity. Moreover, the luminescence properties of 2,3,5-trisubstituted pyrazine derivatives were compared, and the effect of three substituents on the fluorescence of trisubstituted pyrazine derivatives was analyzed by means of different contribution of the basis functions localized on pyrazine fragment into the highest occupied molecular orbital and lowest unoccupied molecular orbital. The oscillator strengths in the excited state (_em) for the pyrazine derivatives substituted by styryl are larger than that of other derivatives with acetylamino and indole groups substituted at 2-site and 5-site of the pyrazine core, and the _em of 3-indolyl pyrazine derivatives is larger than that of 3-styrene pyrazine derivatives. It suggests that the styrene group has a great influence on the luminescence property. In addition, the indole group substituted at 3-site of the pyrazine derivatives can also promote the fluorescence property.