DFT and TDDFT Studies of Silicon Analogs of Fluorescein Derivatives

Fluorescein derivatives play an important role in the field of biological and fluorescent sensors. To tune the spectroscopic properties many attempts have been made including extending conjugation, substituting the central carbon by nitrogen or introducing electron withdrawing groups and replace the oxygen bridge atom by other elements such as N, C, S, Se, and Te. In this paper we report density functional theory (DFT) and time-dependent DFT (TDDFT) studies of silicon analog of fluorescein derivatives with oxygen replaced by Si, C, and Ge. Among the different silicon analogs, the most conjugated molecule 4 showed red shift in absorption wavelength (495 nm). The OH position of molecule 2 has a significant effect on the spectral properties of the silicon analogs of the fluorescein. Since aggregation is very common in most of the fluorescein and it is interesting to study the effect of aggregation, we also studied dimerization of molecule 1 in silicon analog of fluorescein derivative and the results show that two absorption bands are formed with red shift compared to monomer.