Tuning the photoinduced electron transfer in near-infrared heptamethine cyanine dyes

An efficient photoinduced electron transfer (PET) system in near-infrared region was described. The PET in heptamethine cyanine dyes was tuned by changing the electron-donating ability of the substituent at the central position of the polymehine chain. 4-Aminophenylthio-substitution led to an efficient PET and the lowest fluorescence quantum yield. The acetylation, protonation or transition metal cation coordination of the amino group could recover fluorescence greatly via suppressing the PET.