Nonlinear absorption and optical limiting performance of broad-band multi-branched aniline derivatives in the near-infrared region

A thorough investigation was conducted into the impact of pi-linker and acceptor group modifications on the nonlinear absorption coefficient and optical limiting (OL) capabilities of multi-branched aniline derivatives. In the experiment, the femtosecond Z-scan technology and the OL experiment were used to detect the nonlinear optical (NLO) response of the samples dissolved in DMF solution at different wavelengths and energies. The femtosecond Z-scan experiments show that all samples exhibit reverse saturable absorption (RSA) caused by excited state absorption (ESA) induced by two-photon absorption (2PA) at specific wavelengths. NBTT still exhibits strong RSA properties at the near-infrared wavelengths, and the 2PA cross-section can reach 293 GM and 289 GM under the incident laser at the wavelength of 900 nm and 1030 nm, while maintaining strong two -photon-induced ESA. Furthermore, the femtosecond OL experiments reveal the commendable OL property of NBTT, and the limiting thresholds reach 0.0026 J/cm(2) (at 800 nm) and 0.0033 J/cm(2) (at 1030 nm). Quantum chemistry calculations utilizing density functional theory (DFT) show that pi electrons contribute differently to the bond order on different branches of multi-branched molecules, and the value of Branch 1 is greater than or equal to that of the other two branches at the same position. This leads to the charge transfer (CT) of the molecules NBC and NBTC predominantly concentrated on Branch 1 during the 2PA process, while the addition of conjugate units and cyano-groups in the acceptor groups makes the CT of NBTT not only concentrated on Branch 1, but also extended to Branches 2 and 3. This research seeks to develop the structural design and practical application of multi-branched aniline derivatives to achieve high nonlinear absorption capacity, while maintain a low OL threshold in the near-infrared spectral range.