Tuning the Nature of the Fluorescent State: A Substituted Polycondensed Dye as a Case Study

Authors

  • Dr. Cristina Sissa,

    1. Dipartimento di Chimica, Università di Parma and INSTM UdR-Parma, Parco Area delle Scienze 17A, 43124 Parma (Italy), Fax: (+39) 0521-905556
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  • Dr. Valentina Calabrese,

    1. Istituto di Scienze e Tecnologie Molecolari (ISTM), Consiglio Nazionale delle Ricerche (CNR) via C. Golgi 19, 20133 Milano (Italy)
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  • Dr. Marco Cavazzini,

    1. Istituto di Scienze e Tecnologie Molecolari (ISTM), Consiglio Nazionale delle Ricerche (CNR) via C. Golgi 19, 20133 Milano (Italy)
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  • Dr. Luca Grisanti,

    1. Dipartimento di Chimica, Università di Parma and INSTM UdR-Parma, Parco Area delle Scienze 17A, 43124 Parma (Italy), Fax: (+39) 0521-905556
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  • Prof. Francesca Terenziani,

    1. Dipartimento di Chimica, Università di Parma and INSTM UdR-Parma, Parco Area delle Scienze 17A, 43124 Parma (Italy), Fax: (+39) 0521-905556
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  • Dr. Silvio Quici,

    1. Istituto di Scienze e Tecnologie Molecolari (ISTM), Consiglio Nazionale delle Ricerche (CNR) via C. Golgi 19, 20133 Milano (Italy)
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  • Prof. Anna Painelli

    Corresponding author
    1. Dipartimento di Chimica, Università di Parma and INSTM UdR-Parma, Parco Area delle Scienze 17A, 43124 Parma (Italy), Fax: (+39) 0521-905556
    • Dipartimento di Chimica, Università di Parma and INSTM UdR-Parma, Parco Area delle Scienze 17A, 43124 Parma (Italy), Fax: (+39) 0521-905556
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Abstract

An extensive spectroscopic analysis is presented of an elongated polycondensed dye with a donor–acceptor substitution. The charge-transfer (CT) state, polarized along the long molecular axis, is close in energy to a local excitation (LE) of the polycondensed system, roughly polarized along the short molecular axis, which makes this system particularly suitable to investigate the subtle LE/CT interplay. An essential-state model is presented that quantitatively reproduces absorption and fluorescence spectra, as well as fluorescence emission and excitation anisotropy spectra collected in solvents of different polarity and viscosity, which sets a sound basis for the understanding of how solvent polarity and solvent relaxation affect the nature of low-lying excitations. The markedly different fluorescence emission and excitation anisotropy spectra measured in glassy and liquid polar solvents unambiguously demonstrate the major role played by solvent relaxation in the definition of fluorescence properties of the dye.

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