The triplet state of 4‐nitro‐N, N‐dimethynaphthylamine

Abstract

AbstractNanosecond laser photolytic studies of 4‐nitro‐N,N‐dimethylnaphthylamine (4‐NDMNA) in nonpolar and polar solvents at room temperature show a transient species with an absorption maximum in the 500‐510‐nm range. This species is assigned to the lowest triplet excited state of 4‐NDMNA. The absorption maximum of this state is independent of solvent polarity, and its lifetime is a function of the hydrogen donor efficiency of the solvent. In n‐hexane the lifetime 1/k of the triplet state is 9.1 × 10−6 sec, while in acetonitrile 1/k is 2.0 × 10−7 sec. The hydrogen abstraction rate constant kH of the triplet state with tributyl tin hydride (Bu3SnH) in n‐hexane is 1.7 × 107M−1·sec−1, while in the case of isopropyl alcohol as hydrogen donor, kH is 4.0 × 107M−1·sec−1. The activation energy for the hydrogen abstraction by the triplet state from Bu3SnH in deaerated n‐hexane is 0.6 kcal/mol. The lack of spectral shift with increasing solvent polarity, and the appreciable hydrogen abstraction reactivity of the triplet state, also independent of solvent polarity, seem to indicate that this excited state is an n‐π* state which retains its n‐π* character even in polar media.