A rigidified julolidine derivative of 7-(N,N-diethylamino)-4′-hydroxyflavylium is studied.
Its fluorescence emission quantum yield is 2.5 times lower than the non-rigid analog.
Its trans-chalcone does not show cis-trans photoisomerization.
The results demonstrate that the Twisted Intramolecular Charge Transfer (TICT) model is not operative.
Proton catalysis of the thermal trans-chalcone isomerization is described.