Abstract
Two thiophene derivatives(TH-17 and TH-19) were synthesized and the ultra-fast nonlinear optical (NLO) performance was investigated using z-scan technique. Both compounds exhibit NLO response of reverse saturated absorption(RSA) in wide wavelength range (560 nm–800 nm). Intrinsic multi-photon absorption is considered to cause performance. The mechanism of two-photon absorption(TPA) and TPA induced excited-state absorption (TPA-ESA) was introduced to explain the progress. Several primary nonlinear coefficients, including the two-photon absorption(TPA) coefficients and TPA cross section, were calculated. TH-19 displays superior NLO response than TH-17 at all wavelengths due to better electron delocalization and the TPA coefficient in 10−12(m/w) order of magnitude at 560 nm is obtained. The NLO performance is also better than several anthracene derivatives and chalcone derivatives with similar molecular structure reported recently. The substituted terminal thiophene is proved to improve the NLO properties due to the enhancement of π-electron delocalization. Moreover, the excited-state absorption was investigated via femtosecond transient absorption experiment. Intense excited-state absorption at the region of 550 nm–750 nm is observed according to the transient absorption(TA) spectrum. The kinetic processes are analyzed and four relaxation processes(TH-19) of 0.25 ps, 4.5 ps, 188ps and 2.43ns are obtained. The enhanced NLO response and changing region of excited-state absorption indicates the fine-tuned performance of NLO response via the change of terminal substituents.
Published Version
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