This article reports on a comprehensive study of the two-photon absorption (2PA) properties of six novel push-pull octupolar triarylamine compounds as a function of the nature of the electron-withdrawing groups. These compounds present an octupolar structure consisting of a triarylamine core bearing two 3,3′-bis(trifluoromethyl)phenyl arms and a third group with varying electron-withdrawing strength (H < CN < CHO < NO2 < Cyet < Vin). The 2PA cross-sections, measured by using the femtosecond open-aperture Z-scan technique, showed significant enhancement from 45 up to 125 GM for the lowest energy band and from 95 up to 270 GM for the highest energy band. The results were elucidated based on the large changes in the transition and permanent dipole moments and in terms of (i) EWG strength, (ii) degree of donor-acceptor charge transfer and (iii) electronic coupling between the arms. The 2PA results were eventually supported and confronted with theoretical DFT calculations of the two-photon transition oscillator strengths.

This paper reports on the strong two-photon absorption (2PA) of the trans-Pt(PBu3)2(CC–C6H4–CC–C6H4–CC–C6H5)2 (PE3) platinum acetylide complex dissolved in dichloromethane in the visible and near-infrared region. The 2PA spectrum was measured though the open-aperture Z-scan technique using an amplified femtosecond laser system (150 fs) operating at low repetition rate (1 kHz). Since PEs present short intersystem crossing time (ps) and long phosphorescence time (μs), the 2PA cross-section obtained from the Z-scan technique may have contribution from the triplet states. However, we show by a rate equations model and pump–probe experiments that the rate of population transferred to the triplet state via 2PA, employing a 150 fs laser, and low repetition is negligible (<1%). Consequently, 2PA cross-section from tens to thousands of GM units, observed along the nonlinear spectrum, is due to pure singlet–singlet transitions. Our results also reveal that the 2PA spectrum of PE3 in dichloromethane exhibits two 2PA allowed bands centered at 760 nm (120 GM) and 610 nm (680 GM) and is very intense for wavelengths below of 500 nm (>1000 GM). The first 2PA band was attributed to the S0 → S1 (11Ag-like → 11Bu-like) transition, which is made possible because of a relaxation of the selection rules for PE3 that, in solution, present centrosymmetric and noncentrosymmetric conformers. The second 2PA band was ascribed to the S0 → S2 (11Ag-like → 31Ag-like) transition strongly 2PA allowed characteristic in PE’s chromophores. On the other hand, the sizable 2PA cross-section observed for the region 460–500 nm was ascribed to a double resonance effect and high singlet excited state absorption (S0 → S n ).