The dynamics of intramolecular excited state relaxation of N-anthryl substituted pyridinium cations.

N-(1-Anthryl)-2,4,6-trimethyl-pyridinium (I), N-(2-anthryl)-2,4,6-trimethyl-pyridinium (II) and 10-(1-anthryl)-1,2,3,4,5,6,7,8-octahydro-acridinium cations (III) with anomalously high fluorescence Stokes' shift have been investigated. Fluorescence kinetics analysis at various temperatures showed that in the range 293-77 K, the radiative deactivation rate constants (kf) increase by 5.5 to 30 times. The low-temperature time-resolved emission spectra of I-III were found to be consistent with the model: A--> A*<--> B* where A* is the local excited twisted form and B* is the relaxed more planar, bent conformer of the molecule. The rate constants of the excited relaxed state formation (k1) and back reaction (k-1) of compounds studied were estimated.