Photophysics and photostability of 9,10-bis(phenylethynyl)anthracene revealed by single-molecule spectroscopy

Abstract

The photophysics and photostability of 9,10-bis(phenylethynyl)anthracene (BPEA) diluted in a 40-nm-thick Zeonex polymer film have been investigated by single-molecule spectroscopy (SMS). The single-molecule detection of BPEA was verified by recording fluorescence intensity trajectories, fluorescence lifetimes, and fluorescence spectra. The intensity trajectories showed frequent on/off blinking and one-step photobleaching behaviors. The observed blinking was attributed to the temporary occupation of the excited triplet state T₁via intersystem crossing (ISC). Assuming a three-state model (e.g., S₀, S₁, and T₁), the distributions of triplet lifetime and S₁→T₁ ISC quantum yield of BPEA were both derived from the analyses of the blinking statistics and the intensity autocorrelation. We found extremely low ISC yields (on the order of 10⁻⁵–10⁻⁴), which were theoretically rationalized by the large energy gap between ³B_2u and S₁(¹B_1u)/T₁(³B_1u) states. SMS measurements were also conducted under both air and Ar atmospheres in order to gain insight into the influence of oxygen on photobleaching. The results reveal that, although the presence of oxygen considerably degraded the photostability of BPEA, under deoxygenated conditions, BPEA delivers more than 10⁷ photons before photobleaching and possesses an appreciably low photobleaching yield of 10⁻⁹–10⁻⁸. This study shows that BPEA has a relatively high degree of photostability at room temperature and can serve as a useful green fluorescent probe for SMS studies.