Photochemical properties of (7-benzothiazol-2-yl-9,9-didecylfluoren-2-yl)diphenylamine under one- and two-photon excitation

The photochemical properties of the fluorene derivative (7-benzothiazol-2-yl-9,9-didecylfluoren-2-yl)diphenylamine (1) in hexane and CH2Cl2 were studied under linear (one-photon) and nonlinear (two-photon) excitation. The quantum yield of the photochemical reaction, Φ, for 1 in hexane was in the range (3.5–5)×10−5 for one-photon excitation (UVGL-25 and Xe-lamps) and was nearly the same under two-photon excitation (femtosecond laser with pulse duration 120 fs, average power ∼10 mW, repetition rate f=1 kHz). The values of Φ in CH2Cl2 were (2.5–4)×10−5 for one-photon excitation and increased 50–80 times under two-photon excitation. This increase can be explained by an additional one-photon absorption process from the first electronically excited state, resulting in the observed enhancement in photochemical decomposition.