Fluorescent detection of singlet oxygen: Amplifying signal transduction and improving sensitivity based on intramolecular FRET of anthryl appended porphyrins

Two new anthryl-appended porphyrin dyads have been synthesized and used as highly selective and sensitive fluorescence probes for singlet oxygen (1O2). The design strategy for the probes is directed by the idea of intramolecular fluorescence resonance energy transfer (FRET) interactions and carried out by incorporation of an electron-rich fluorophore (porphyrin) with a reactive anthracene for 1O2. The molecular recognition is based on the specific interaction of 1O2 with the inner anthracene moiety, and the signal reporter for the recognition process is the porphyrin fluorescence. As a result of overlap of the emission band of the anthracene with the absorbance band of the porphyrin, intramolecular FRET occurs between the anthracene (donor) and the porphyrin (acceptor). The effective light absorbed by the porphyrin and, concomitantly, the emitted light intensity are thus modulated by the emission intensity of the anthracene. Upon reaction with reactive oxygen species such as hydrogen peroxide, hypochlorite, superoxide, hydroxyl radicals, and 1O2, the probes exhibit a selective response toward 1O2. In addition, significant amplification of the signal transducer is observed. The feasibility of the design was demonstrated by monitoring the 1O2 generated from a MoO 4 2− /H2O2 system. The results clearly demonstrate that the synthesized probes exhibit both high selectivity and high sensitivity for 1O2. The fluorescence reaction and signal amplification mechanism of the system were both discussed, clearly confirming that the introduction of electron-rich porphyrin units into the 9,10-positions of anthracene can improve the response sensitivity and activate the probe’s reactivity toward 1O2.