Salt-cocrystal continuum for photofunction modulation: Stimuli-responsive fluorescence color-tuning of pyridine-modified intramolecular charge-transfer dyes and acid complexes

Yoshio Yano, Toshikazu Ono, Sou Hatanaka, Daniel T. Gryko, Yoshio Hisaeda

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1 Citation (Scopus)


The regulation of proton transfer dynamics between acid-base complexes is of significant interest in the pharmaceutical industry and materials chemistry. However, the extent of proton transfer in the solid state is difficult to predict, and identifying the salts (protonation), cocrystals (hydrogen bond), and salt-cocrystal continuum (partially protonated states) remain challenging topics. Here we report that the three states (salts/cocrystals/salt-cocrystal continuum) can be distinguished by photoluminescent color changes based on acid-base complexes consisting of a pyridine-modified pyrrolopyrrole dye and organic acids. Structure-property relationships of 10 complexes indicated that ΔpKa value (pKa (protonated base)-pKa (acid)) and the crystalline environment determine the extent of proton transfer, which governs the intramolecular charge-transfer (ICT) strength of the complexes and tunes the photoluminescence properties. Enhancement of the ICT strength leads to a bathochromic shift of emission from blue to green to yellow under UV light. The salt-cocrystal continuum (0 < ΔpKa < 3) showed vapochromism/vapofluorochromism against CH2Cl2, owing to the extent of proton transfer from the acid to the pyridine moiety of the dye being modulated by inclusion and desorption of CH2Cl2. This study suggests that the rational design of photoluminescent acid-base complexes is useful for obtaining novel photofunctional materials.

Original languageEnglish
Pages (from-to)8847-8854
Number of pages8
JournalJournal of Materials Chemistry C
Issue number29
Publication statusPublished - Jan 1 2019


All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Chemistry

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