The charge transfer mechanism and spectral properties of a near-infrared heptamethine cyanine dye in alcoholic and aprotic solvents

Abstract

The charge transfer mechanism of a synthesized near-infrared (NIR) heptamethine cyanine dye has been studied with 3D real space analysis method. A new phenomenon about the intramolecular charge transfer (ICT) process is observed: the sulfonate (–SO 3 −) groups are mainly concerned with the ICT process. The electrons can transfer from the sulfonate (–SO 3 −) groups to the bridgehead amine and the electron-defect conjugated system. And the absorption and fluorescence spectra of the ICT state in alcoholic and aprotic solvents are analyzed. The spectral regularities are explained by the Kamlet and Taft ( π *, α, β) scale and the ICT mechanism. Specific hydrogen-bonding interactions between the solute and solvent are considered to explain the different spectral regularities of the dye in alcoholic and aprotic solvents.