Enhanced Quenching in an Azaphthalocyanine–Ferrocene Supramolecular Dyad upon Charge-Transfer Complex Formation

High Resolution Image Download MS PowerPoint Slide Azaphthalocyanines are fluorescent dyes and photosensitizers with promising applications in photodynamic therapy (PDT) and fluorescence sensing. However, achieving precise control over their photophysical behavior remains a major challenge. Here, we report a supramolecular approach to enhance fluorescence quenching via charge-transfer complex formation. An electron-deficient azaphthalocyanine derivative incorporating a naphthalene-2,6-diol moiety as a charge-transfer donor was synthesized, and its fluorescence response toward a tailored quencher was evaluated. A ferrocene–methylviologen conjugate that simultaneously functions as a quencher and an acceptor in charge-transfer complexes was designed and synthesized for this purpose. Compared to ferrocenemethanol and methylviologen alone, the conjugate quencher exhibited an enhanced quenching efficiency in acetonitrile. The quenching followed a nonlinear Stern–Volmer dependence, indicating both static and dynamic quenching mechanisms, with the former one being more efficient with K S = 241 M –1 due to directed charge-transfer complex formation between methylviologen and the naphthalene-2,6-diol moiety serving as a staple. These findings demonstrate that complexation can enhance the fluorescence quenching of AzaPc derivatives and suggest a general approach for designing responsive photosensitizers in smart PDT systems or molecular sensing.