Some photochemical reactions of aromatic hydrocarbons and related compounds.

The photophysical and photochemical properties of aromatic hydrocarbons have been reviewed. Aromatic hydrocarbons were photoreduced upon irradiation in the presence of amines, and also photosensitized the decarboxylation of amino acids. Product and kinetic studies have shown that both these reactions involve the same initial step, i.e. transfer of an electron from the amino function to the first excited singlet state of the aromatic hydrocarbon. Products obtained from the decarboxylation of amino acids photosensitized by dyes and aromatic carbonyl and aza-aromatic compounds were identical with those obtained from the decarboxylations sensitized by aromatic hydrocarbons. The mechanism for photodecarboxylation by all these sensitizers was proposed to be the same. Amino alcohols quench the fluorescence of aromatic hydrocarbons less efficiently than do amines. This inefficiency has been attributed to hydrogen bonding between the hydroxylic proton and the nitrogen atom of the amino alcohol. Two series of compounds (naphthylalkylamines and anthrylalkylamines) where intramolecular exciplex formation would be expected to occur have been synthesised. A study of the emission from these compounds has shown that the geometrical requirements for exciplex formation are less stringent than for excimer formation. Intramolecular exciplex formation reduces the photoreactivity of these compounds. The introduction of a tertiary amino group into an aromatic hydrocarbon molecule has been shown to protect the aromatic hydrocarbon against photosensitized oxidation. This protection has been shown to operate on a number of different types of molecule. Deactivation of singlet oxygen is thought to be the method of protection. Aromatic hydrocarbons have been shown to be photo-reduced in the presence of tri-n-butyltinhydride. Kinetic studies have shown the triplet state of the aromatic hydrocarbon to be the excited state involved in the photoreduction.