PHOTOPHYSICS OF PHENYL PYRIDINES AND BIPYRIDINES IN DIFFERENT MEDIA

Analysis of absorption and emission spectra of 2,4'-bipyridine (2BPy), 4,4'-bipyridine (4BPy) and three isomeric phenyl pyridines (PhPy) in different solvents reveal that the general nature of lowest emitting state is pi,pi*. A significant enhancement of fluorescence of 2PhPy at 77 K in relation to 3PhPy has been attributed to a possible through-space interaction of n- and pi-electronic clouds. A discernible feature for phenyl pyridines is the increased basicity and polarity in the excited singlet state. The internal conversion seemed to be active in both phenyl pyridines and bipyridines in MCH solvent and for bipyridines in ethanolic solution, the second-order spin-orbit coupling comes into picture.