Triplet excited states of nitronaphthalenes. II. b‐Nitronaphthalene

Abstract

AbstractNanosecond flash photolysis of b‐nitronaphthalene (b‐NO2C10H7) in nonpolar and polar solvents shows a transient species with maximum absorption and lifetime dependent on solvent polarity. In deaerated n‐hexane the absorption maximum and lifetime (1/k) are 425 nm and 530 nsec, while in deaerated ethanol the corresponding values are 470 nm and 1.7 ·sec. This transient absorption is attributed to the triplet excited state of b‐NO2C10H7, and the observed red shift as well as its longer lifetime in polar solvents are indicative of the intramolecular charge transfer character of this state. The change of dipole moment accompanying the transition T1 → Tn, as well as rate constants for electron and proton transfer reactions involving the T1 state of b‐NO2C10H7, were determined. The spectroscopic and kinetic data obtained in this work indicate that the triplet state of b‐NO2C10H7 behaves like a n‐π* state in nonpolar media, while in polar solvents the n‐π* character of the state is reduced with a simultaneous increase in the charge transfer character.