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

Abstract

Singlet oxygen (1 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 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 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 O 2 is generated using the standard photosensitizer Rose Bengal, which is followed by estimation of the rate of reaction of 1 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 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.

Caging and photo-triggered uncaging of singlet oxygen by excited state engineering of electron donor–acceptor-linked molecular sensors

“…1 a) was synthesized by a one-step reaction started from 7-amino-4-methylcoumarin and 9-chloromethylanthracene, and characterized by the spectroscopic methods including NMR spectrometry (see “ Methods ” section). First, we confirmed that 1 is nonfluorescent because of the intramolecular electron transfer from the anthracene moiety to coumarin moiety of 1 19 , 20 . 1 reacts with 1 O 2 generated by the photosensitization of Rose Bengal (RB) by green light to form a moderately fluorescent endoperoxide 1 - O 2 (Fig.…”

“…Remarkably, the fluorescence quantum yield of 1 - O 2 was found to be ϕ ~ 0.03 and is not as high as commercially available fluorogenic 1 O 2 probe molecules which form the endoperoxide in the fluorescent form ( ϕ > 0.5) 5 , 7 although the original dye part of 1 - O 2 (i.e., 7-amino-4-methyl coumarin; Coumarin 120) is highly fluorescent ( ϕ = 0.62) 19 . This result implies the huge fluorescence intensity enhancement possibility during 1 O 2 sensing and the existence of a non-radiative relaxation pathway in the photoexcitation of 1 - O 2 , which is discussed below.…”

“…Figure 1 b shows the absorption spectra of 1 recorded as a function of time under the photosensitization of RB. The intensities of the anthracene's vibrational bands at 390 nm and 370 nm are decreased by the 1 O 2 mediated oxidation of the anthracenyl moiety 19 , 26 . After the UV illumination, the absorbance around 290 nm was remarkably increased, suggesting the formation of the endoperoxide 1-O 2 26 .…”

Unexpected Boost in Activity of a Cu(I) Photosensitizer by Stabilizing a Transient Excited State

“…The assignment of the NIR luminescence to 1 O 2 was further verified by a decrease in intensity in the presence of the 1 O 2 quencher 9-methylanthracene (see Figure S53). The singlet oxygen quantum yields (ϕ ( 1 O 2 )) were determined in THF solution relative to the Cr­(III) reference complex Cr­(ddpd) 2 (BF 4 ) 3 (ddpd = N , N ′-dimethyl- N , N ′-dipyridine-2-ylpyridine-2,6-diamine) (ϕ ref ( 1 O 2 ) = 61% in dimethylformamide (DMF)) . Importantly, Cudmbiipo showed the highest ϕ ( 1 O 2 ) of 68%, outperforming its congener Cubiipo (53%) and the reference system Cubcp (44%) under identical conditions.…”

Excitation‐Wavelength‐Dependent Functionalities of Temporally Controlled Sensing and Generation of Singlet Oxygen by a Photoexcited State Engineered Rhodamine 6G‐Anthracene Conjugate

“…Regarding 1 O 2 sensing, most of the recently developed 1 O 2 sensing molecules are combinations of fluorophores and 1 O 2 scavenger moieties like anthracene [9,12–15] . A general theory suggests fluorescence in such pristine sensor molecules is quenched because of photoinduced intramolecular electron transfer (PIET).…”