Photophysics of manisyl-substituted 2-pyridin-2-yl-1,10-phenanthrolines. Dual emission dependent on structure and solvent.

Systematic variation of the substitution pattern of 2-pyridin-2-yl-1,10-phenanthrolines with 4-methoxy-2,6-dimethylphenyl (manisyl) groups alpha, beta, and gamma to the nitrogen atoms results in a 3 x 3 array of pyridyl-phenanthrolines displaying low to high quantum yields (Phi(f) = 0.03-0.60). Photophysical studies elucidated a duality of emissive states: a weakly emissive, locally excited state, similar to the (1)pi,pi state of phenanthroline; and a strongly emissive, charge-transfer state, dependent on manisyl regiochemistry and solvent polarity. Ab initio calculations underscore the similarities in the electronic structures of phenanthroline and pyridyl-phenanthrolines rather than between terpyridine and pyridyl-phenanthroline.