The study of ground state and excited state properties of cyanine dyes by using computational chemical methods

Abstract

The 5,5.,6,6.-tetrachloro-1,1.,3,3.-tetraethyl-benzimidazolo carbocyanine (TTBC) iodide, abbreviated CBIC2(3) or JC-1, is used for the molecular probe especially as measuring mitochondrial membrane potential and allows to visualize mitochondria, apoptosis or not.The behaviors of the TTBC at the ground and excited states have been investigated by using quantum chemical methods. DFT/6-31G** levels of theory calculations have been carried out for the optimization and the frequencies with B3LYP and PBEPBE functionals for the ground state structure. TDDFT/6-31G** and CIS/6-31G** methods have been used for the excited state properties. In addition to those, solvation calculations were performed with CPCM and IEFPCM.The effects of the functional groups, length of the conjugated chain, and alkyl groups on TTBC have been analyzed. There is no significant effect of functional groups either as donor or acceptor on the optimum structure. Only the alkyl groups change the planarity of the molecule. TTBC has a very rigid geometry. But it is possible to tune up max with NH2 and butyl/propyl and increasing polymethine chain length.To explain the shoulder on the fluorescence spectrum, the PES section was obtained. The fluorescence property of TTBC was compared with the experimental data. Although perpendicular structure is favorable in the first excited state, there is no significant difference in dipoles. The twisted charge transfer state is absent in this dye based on these calculations. The solvent effect on TTBC in different solvents was investigated. The solvation calculations show that, max values are independent of the polarity of the solvents as seen experimentally.