THE EFFECT OF INTERNAL-ROTATION ON ABSORPTION AND FLUORESCENCE OF DYE MOLECULES

Internal rotation around an essential single bond within a chromophoric system very often leads to a hypsochromic shift of the longest-wavelength absorption band, associated with a decrease in absorption coefficient and an increase of Stokes shift. In the case that a non-fluorescent nπ* state lies near to a fluorescent CT state, this hypsochromic shift can cause a dramatic drop of the fluorescence quantum yield and/or a strong dependence of it on solvent polarity. © 1990.