Kinetics of singlet oxygen sensing using 9-substituted anthracene derivatives$$^{\#}$$

Abstract

Singlet oxygen ( $$^{1}\hbox {O}_{2}$$ ), the lowest excited-state of molecular oxygen receives great attention in basic research and clinical and industrial settings. Despite several spectroscopic methods available for $$^{1}\hbox {O}_{2}$$ sensing, fluorescence sensing receives great attention, for which many fluorogenic sensors based on substituted anthracene are reported. Nonetheless, the roles of substituents on the sensing efficiency, in terms of detection time, remain largely unknown. In this work, we examine the $$^{1}\hbox {O}_{2}$$ sensing efficiency of a fluorescence sensor based on a coumarin–anthracene conjugate, which is an electron donor-acceptor dyad, and compare the efficiency with that of 9-methylanthracene. Here, $$^{1}\hbox {O}_{2}$$ is generated using the standard photosensitizer Rose Bengal, which is followed by estimation of the rate of reaction of $$^{1}\hbox {O}_{2}$$ to the sensor and 9-methylanthracene. The second order reaction rate of the sensor is an order of magnitude less than that of 9-methylanthracene. The lower reactivity of the sensor to $$^{1}\hbox {O}_{2}$$ suggests that the roles of substituents, such as electronic interactions, steric interactions and the reactivity of precursor complexes, on sensing efficiency should be carefully considered during construction of fluorogenic molecular sensors. SYNOPSIS The kinetics of singlet oxygen sensing using a 9-substituted anthracene derivative is studied by comparing the photooxidation rates of a conjugate between 9-methyl anthracene and a coumarin dye. The singlet oxygen sensing rate points out that the electronic interaction and steric effect induced by the substituents on anthracene influence the kinetics of sensing.