The
nonlinear absorption properties and excited-state dynamics
of two linear D−π–A pyrene derivatives (B1 and
B2) with different push–pull properties were investigated and
compared. The transient absorption spectra provide information about
their excited states, revealing a transition from the local excited
(LE) state to the charge transfer (CT) state in each of the compounds.
The Z-scan measurements show that both derivatives
exhibit reverse saturable absorption at multiple excitation widths
(fs, ps, and ns). Combined with quantum chemical calculations, the
experimental results indicate that B1 (with pyrene as the donor) shows
superior two-photon absorption (TPA) at shorter wavelengths (≤650
nm) because of more π–π* transition and that the
stronger CT to the pyrene group contributes to the resonance enhancement
of the TPA of B2 (with pyrene as the acceptor) at near-infrared wavelengths.
In addition, both compounds exhibit satisfactory optical limiting
performance, while the thresholds of B2 are 0.0029–0.01 and
0.092 J/cm2 under excitation by femtosecond (532–900
nm) and picosecond (532 nm) pulses, respectively.