Rational design of fluorescent viscosity sensors by the principle of photoinduced electron transfer

To establish a new strategy for the development of fluorescent viscosity sensors by the principle of photoinduced electron transfer, three 4-aminonaphthalimide based D-(CH2)2-A molecules were designed and synthesized. The effects of solvent polarity and viscosity on the fluorescence spectra of these compounds were investigated. These compounds exhibit viscosity-sensitive fluorescence spectra in ethylene glycol–glycerol mixtures. A mechanism about exciplex formation was proposed to explain their viscosity sensitivity.