Spectral study, stability and protein labeling of two Carbazole-Benzothiazole derivatives

3-benzothiazole-9-ethyl-carbazole (BEC) and 3,6-di-benzothiazole-9-ethyl-carbazole (DBEC) were synthesized by using carbazole as base and then characterized by 1H NMR. The optical properties of them were investigated and compared with carbazole and 9-ethyl-carbazole. The photostability and thermostability of the compounds were studied and the results indicated they are both very stable. Effects of solvent properties including polarity, viscosity and refractive index on the spectra properties of the compounds were investigated. Quantum yield of the compounds in organic solvent was also determined and it is found the most complex compound has the highest quantum yield up to 0.68. Finally the synthesized compounds were used to label bovine serum albumin (BSA) protein and simultaneously stability constant (Ks) between them is calculated and compared with other similar dyes. The results showed that the fluorescent intensity of the compound is increased significantly after labeling with BSA protein.