Conveniently modified polycyclic aromatic hydrocarbon (PAH) fluorophores are obtained by a bromination–borylation sequence. The bis-borylated dyes show red-shifted absorption (λabs,max > 450 nm) and emission (λf,max > 500 nm; Φf: 0.3–0.5) properties as compared to the parent PAHs. Their centrosymmetric A–π-A (A: acceptor) structures led to the observation of two-photon absorption (up to 60 GM) in the near-infrared spectral region (>800 nm). The rigid structure shuts down non-radiative deactivation by limiting rotational or vibrational freedom. Thus, the excited-state pathways originating from the excited singlet state are resumed to fluorescence and excited triplet-state formation. The latter is involved in the energy-transfer sensitization of singlet oxygen (ΦΔ: 0.50–0.66). This bipartition provides the setting for the concomitant observation of fluorescence and photosensitization, making these dyes ideal bimodal chromophores.
We are grateful for financial support from the Spanish Ministerio de Ciencia e Innovación (grant PID2020-119992GB-I00 for U. P., PID2019-106358GB-C21 and PID2019-106358GB-C22 for A. R., PID2019-110441RB-C33 for F. B., PID2019-104293GB-I00 for F. N and E. P.-I, and doctoral fellowship PRE2020-092646 for P. V.-D.), the European Research and Development Fund (ERDF), the Consejo Superior de Investigaciones Científicas (grant 202080I005 for A. R.), the Junta de Andalucía/University of Malaga (grant UMA18-FEDERJA-007 for F. N. and E. P.-I.), and the Junta de Andalucía/University of Huelva (grant UHU-202070 for U. P.). Dr Z. Domínguez (University of Huelva) is acknowledged for technical assistance in the early phase of this work.