Naphthoxazole-Based Singlet Oxygen Fluorescent Probes

In this study, we report the synthesis and photochemical behavior of a new family of photoactive compounds to assess its potential as singlet oxygen (1O2) probes. The candidate dyads are composed by a 1O2 trap plus a naphthoxazole moiety linked directly or through an unsaturated bond to the oxazole ring. In the native state, the inherent great fluorescence of the naphthoxazole moiety is quenched; but in the presence of 1O2, generated by the addition and appropriate irradiation of an external photosensitizer, a photooxidation reaction occurs leading to the formation of a new chemical entity whose fluorescence is two orders of magnitude higher than that of the initial compound, at the optimal selected wavelength. The presented dyads outperform the commonly used indirect fluorescent 1O2 probes in terms of fluorescence enhancement maintaining the required specificity for 1O2 detection in solution. Conjugation of a fluorescent and a singlet oxygen trapping moieties leads to a dyad with a low fluorescence in its native state. In the presence of singlet oxygen, a new photooxidized chemical entity is born, leading to a fluorescence enhancement over two orders of magnitude at the optimal selected wavelength.