The interaction of ground and excited states of lumichrome with aliphatic and aromatic amines in methanol

Encinas, MV; Bertolotti, SG; Previtali, CM

Abstract

The reaction of the ground and excited states of lumichrome (= 7,8-dimethylalloxazine = 7,8-dimethylbenzo[g]pteridine-2,4(1H,3H)-dione) with aliphatic and aromatic amines was investigated in MeOH. In the presence of aliphatic amines of high basicity, new bands are observed in the absorption and fluorescence spectra. These bands arise in a proton-transfer reaction from lumichrome, in the ground and in the singlet excited states, to the amine. On the other hand, amines with lower basicity such as triethanolamine (=2,2?,2?-nitrilotris[ethanol]) and aromatic amines are not able to deprotonate lumichrome, and hence a quenching of the fluorescent emission takes place without changes in the spectral shap. In this case, bimolecular-quenching rate constants were determined for the excited singlet and triplet states. Based on photolysis experiments, an electron-transfer mechanism is proposed. Aliphatic amines yield lower rate constants than the aromatic ones for the same driving force. A notable difference arises in the limiting value reached by the singlet and triplet quenching rate constants by aromatic amines. For the singlet quenching, the limit is coincident with a diffusion-controlled reaction, while those for triplet quenching reach a lower constant value, independent of the driving force. This is explained by an electron-transfer mechanism, with a lower frequency factor for the triplet-state process.

Más información

Título según WOS: The interaction of ground and excited states of lumichrome with aliphatic and aromatic amines in methanol
Título según SCOPUS: The interaction of ground and excited states of lumichrome with aliphatic and aromatic amines in methanol
Título de la Revista: HELVETICA CHIMICA ACTA
Volumen: 85
Número: 5
Editorial: WILEY-BLACKWELL
Fecha de publicación: 2002
Página de inicio: 1427
Página final: 1438
Idioma: English
URL: http://doi.wiley.com/10.1002/1522-2675%28200205%2985%3A5%3C1427%3A%3AAID-HLCA1427%3E3.0.CO%3B2-A
DOI:

10.1002/1522-2675(200205)85:5<1427::AID-HLCA1427>3.0.CO;2-A

Notas: ISI, SCOPUS