Fluorescence and excited state proton transfer of pyrene-3-carboxaldehyde |
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Authors: | A U Acua J M Otn |
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Institution: | Instituto de Química Fisica Rocasolano, C.S.I.C., Serrano 119, Madrid-6, Spain |
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Abstract: | In very dilute water solutions, ca 10−7 M, pyrene-3-carboxaldehyde fluoresces with a high quantum yield, øF = 0.98. This emission is quenched at low pH and, if the proton activity is high enough, a new weak, red shifted fluorescence appears. These effects are explained by the existence of a fast proton transfer in the excited state. The emitting singlet is believed to be 6–7 orders of magnitude more basic than the ground electronic state. By measuring the changes in fluorescence intensity and lifetime of pyrene-3-carboxaldehyde as a function of pH, a value for the quenching rate constant k2 = (2.2 ± 0.3) × 1010 M−1 s−1 was obtained. The quenching of the neutral form fluorescence is proposed to be produced by the protonation of the excited aldehyde, followed by a fast radiationless deactivation of the conjugated acid, before prototropic equilibrium can be attained. |
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