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Singlet Excited State Pyridinic Deprotonation of the N9-methylbetacarboline Cations in Aqueous Sodium Hydroxide Solutions

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Abstract

The singlet excited state pyridinic deprotonation of the 9-methyl-9H-pyrido[3,4-b]indole, MBC, cations has been studied in aqueous NaOH solutions by absorption, steady state and time resolved fluorescence measurements. This excited state reaction proceeds through a stepwise mechanism involving different ground and excited state hydrogen bonded MBC-(water)n complexes. Thus, in aqueous NaOH solutions of MBC above pH 8, two ground state hydrogen bonded MBC-water adducts, namely PC and PTC, coexist in equilibrium. Upon excitation, the PC behaves as an independent fluorophore, whereas the PTC reacts with water molecules during its excited state lifetime to give the intermediate CL*. This exciplex is the precursor of the excited state cation, C*. In almost all the pH range, C* is practically the only existing species in the singlet excited state of MBC. In concentrated NaOH solutions beyond the pH range, C* deprotonates giving CL* and PTC* species.

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Acknowledgements

We gratefully acknowledge financial support from the Dirección General Científica y Técnica MEC, CTQ2006-13539 and Junta de Andalucía, 2005/FQM-368, 2007/FQM-106.

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Authors and Affiliations

  1. Departamento de Química Física, Facultad de Farmacia, Universidad de Sevilla, 41012, Sevilla, Spain

    Antonio Sánchez Coronilla, Carmen Carmona, María A. Muñoz & Manuel Balón

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  1. Antonio Sánchez Coronilla
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  2. Carmen Carmona
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  3. María A. Muñoz
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  4. Manuel Balón
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Correspondence to Manuel Balón.

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Sánchez Coronilla, A., Carmona, C., Muñoz, M.A. et al. Singlet Excited State Pyridinic Deprotonation of the N9-methylbetacarboline Cations in Aqueous Sodium Hydroxide Solutions. J Fluoresc 20, 163–170 (2010). https://doi.org/10.1007/s10895-009-0534-3

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