The chemistry of some excited state charge-transfer complexes.
2015-11-19T08:46:04Z (GMT) by
The emission spectra of some alkylnaphthalenes containing amino or hydrazine moieties in the side chain exhibit anomalous fluorescence bands. The spectral data are consistent with the proposal that the bands are derived from intramolecular exciplexes. The steric and electronic requirements for intramolecular exciplex formation are discussed on the basis of the dipole moments, wavelengths of fluorescence maxima and, in the case of the hydrazines, the N.M.R. spectra. Irregularities in the rate constants for intermolecular quenching of 9-methylanthracene fluorescence by hydrazines and in the fluorescence spectra of hydrazines are believed to be due to solute association, probably via hydrogen bond formation. A study of the products obtained by irradiation of certain monoacylhydrazines has been made, it is proposed that reaction proceeds by a photoinduced homolysis of the N - N bond. Salts of N,N-diethy1-2-(1-naphthyl)ethylamine with hydrogen halides and alkyl halides have been shown to exhibit exciplex formation in aprotic solvents. The results are interpreted in terms of electron transfer from the halogen anion to the singly excited naphthalene, followed by a rapid elimination of hydrogen halide or alkyl halide. The fluorescence quenching of cyanosubstituted aromatic hydrocarbons has been shown to proceed via exciplex formation when the hydrocarbons possess a high singlet energy. Intramolecular fluorescence quenching of naphthalene by dienes and olefins does not give rise to a fluorescent complex, this has been explained in terms of the character of the quenching groups. Donor-acceptor complexes formed between imides and amines or aromatic hydrocarbons have been shown to give an excited state charge-transfer complex upon excitation. Enhanced complex formation has been observed upon freezing cyclohexane or aceto-nitrile solutions of the compounds. Ester and ether groups have been used to separate two naphthalene moieties. Excitation yields excited state naphthalene complexes even when the linking chain consists of more than three atoms. Similar complexes have been detected in cyclohexane and acetonitrile matrices, it is suggested that excitation of aggregates or crystals formed upon freezing give rise to the new fluorescence bands.