Multiple relaxation pathways in photoexcited dimethylaminonitro- and dimethylaminocyano-stilbenes

• Published in: Chemical physics letters 1993-06, Vol.208 (1), p.48-58
• Main Authors: Lapouyade, René, Kuhn, Alexander, Letard, Jean-François, Rettig, Wolfgang
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Molecular properties and interactions with photons; Physics
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/0009-2614(93)80075-Z

The photophysical behaviour of para-nitro-, para-cyano- and meta-nitro-4′-dimethylaminostilbenes is compared and explained. The increase of the fluorescence quantum yield with solvent polarity is the result of a negative solvatokinetic behaviour of the nonradiative channel leading to the ground state via the double-bond twisted species P* which is of low-polarity nature. The maximum in the fluorescence quantum yield at intermediate solvent polarities, observable for the nitro compounds, is due to a further nonradiative channel specifically linked with the nitro group and with positive solvatokinetic behaviour. This quenching channel becomes important for high-polarity solvents but is absent for compounds without the nitro group. TICT state formation (twisted nitro group) as a candidate for this channel is discussed.