Contribution of excited state absorption to optical limiting properties in multi-branched structures

Abstract A series of multi-branched compounds D1 – D3 combining a triphenylamine core with one, two or three benzylidene cyclopentylidene malononitrile branches, respectively, were synthesized. The linear photophysical property, photochemical stability, thermal stability, and nonlinear absorption under 1064 nm pulsed lasers with pulse durations in both nanosecond and femtosecond regimes of D1–D3 were investigated. The results showed that the main optical limiting mechanism of D1 – D3 under femtosecond pulses was two-photon absorption (2PA), but their excited state absorption (ESA) became the main contributor for their optical limiting behaviors under nanosecond pulses. Meanwhile, introducing a multi-branched structure has much stronger impact on the ESA spectrum of D3 than on its linear absorption spectrum compared with the monomer D1 . The largest ESA cross-section of D3 was the main contributor to its enhancement of effective 2PA in nanosecond regime. Combining with its best thermal and photochemical stability, the three-branched compound D3 was proved as a good optical limiting material for 1064 nm nanosecond pulsed lasers.