Femtosecond Spectroscopy of Superfluorescent Fluorenyl Benzothiadiazoles with Large Two-Photon and Excited-State Absorption

Abstract

New symmetrical fluorene-containing derivatives with a benzothiadiazole (BTD) central core, 4,7-bis(5-(9,9-didecyl-7-(phenylsulfonyl)-9H-fluoren-2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (1) and 4,7-bis(5′-(9,9-didecyl-7-(phenylsulfonyl)-9H-fluoren-2-yl)-2,2′-bithiophen-5-yl)benzo[c][1,2,5]thiadiazole (2), were prepared, and multifarious linear photophysical and nonlinear optical properties, potentially attractive for a number of emerging applications, were investigated. Comprehensive photophysical and photochemical characterization was performed in a number of organic solvents at room temperature, including linear, one-photon absorption (1PA), steady-state fluorescence, excitation anisotropy, and fluorescence lifetime properties. Fast relaxation processes in the excited states of 1 and 2 with characteristic times of ∼0.2–3 ps were revealed by a femtosecond transient absorption pump–probe method. Large two-photon absorption (2PA) cross sections of 1 and 2 (up to 2500–2700 GM) were obtained by an open ...