Photochemistry of (E)-1-(9-anthryl)-2-(4-nitrophenyl)ethene in the presence of aliphatic amines: H-bonding and charge-transfer effects

Abstract

Polysubstituted aliphatic and aromatic amines and alcohols quench the fluorescence of (E)-1-(9-anthryl)-2-(4-nitrophenyl)ethene (NA). The quenching occurs without modification of the NA emission characteristics, follows a Stern–Volmer (SV) relationship and correlates with the decrease of the photoisomerization and intersystem crossing (ISC) yields. The dependence of the quenching rate constants (k_q) on the ionization potentials suggests a charge-transfer interaction for the amines. The dependence of the k_q values on alcohol acidity indicates the intervention of H-bonding phenomena. The interaction of primary aliphatic amines and NA in low-polarity solvents results in a broadening and a quenching of the NA emission. The quenching does not follow the SV relationship, has no effect on the E → Z photoisomerization nor on the population of the triplet state, and increases the yield of the photobleaching reaction, especially in more polar solvents (chlorobenzene). This peculiar behaviour of primary aliphatic amines is attributed to H-bonded complexes in both the ground and the lowest excited singlet state.