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

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 (–SO3−) groups are mainly concerned with the ICT process. The electrons can transfer from the sulfonate (–SO3−) 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.