In this present paper, we investigate the relationship between the dynamic first-order hyperpolarizability (DFH, or β HRS ) of a triarylamine core bearing two 3,3′-bis(trifluoromethyl)phenyl arms and the nature of a third group containing distinct electronwithdrawing strength (H < CN < CHO < NO 2 < Cyet < Vin). For that, we have combined hyper-Rayleigh scattering (HRS) experiments with picosecond pulse train at 1064 nm and quantum chemical calculations at the density functional theory (DFT) level. The β HRS values exhibited pronounced enhancement from 56 × 10 −30 cm 5 /esu (EWG = CN) up to ∼400 × 10 −30 cm 5 /esu (EWG = Vin) due to the increase in the degree of donor−acceptor charge transfer concomitant with the intensification of the resonance enhancement effect observed when the scattered photon (2ω = 532 nm) approaches, in energy, the lowest energy band of chromophores. Furthermore, our experimental results suggest that the CF 3 group has a significant effect on the β HRS , since we observed a considerable increase in this parameter (at least 30% higher) for CF 3 EWG molecules as compared to their homologous tBu·EWG derivatives, recently investigated. Finally, the β HRS results were compared with theoretical results provided by the coupled perturbed Hartree−Fock method implemented at the DFT level of theory and combined with a polarizable continuum model to take into account the solvent environment. The theoretical results allowed us to evaluate the effects of solvent-induced polarization and frequency dispersion on the first-order hyperpolarizability of the molecules and their molecular anisotropy (or dipolar/octupolar contributions).
We have interpreted the two-photon absorption spectrum of water-soluble copper indium sulfide (CIS) QDs with stoichiometry 0.18 (Cu), 0.42 (In), and 2 (S) and an average diameter of approximately 2.6 nm. For that, we employed the wavelengthtunable femtosecond Z-scan technique and the parabolic effective-mass approximation model, in which the excitonic transition energies were phenomenologically corrected due to the stoichiometry of the nanocrystal. This model considers a conduction band and three valence sub-bands allowing excitonic transitions via centrosymmetric (Δl = ±1, where l is the angular momentum of the absorbing state) and non-centrosymmetric (Δl = 0) channels. In such case, this became relevant because the CIS QDs with chalcopyrite crystalline structure is a non-centrosymmetric semiconductor. Thus, our experimental results pointed out two 2 PA allowed bands located at 715 nm (2hv = 3.47 eV) and 625 nm (2hv = 3.97 eV) with cross sections of (6.3 ± 1.0) x 10 2 GM and (4.5 ± 0.7) x 10 2 GM, respectively. According to the theoretical model, these 2 PA bands can be ascribed to the 1P1/2(h3) → 1S3/2(e) (lower energy band) and 1P1/2(hheavy) → 1S3/2(e) (90%)/(10%)1P1/2(hsplit-off) → 1P3/2(e) (higher energy band) excitonic transitions. A good agreement (magnitude and spectral position) between the experimental and theoretical data were obtained. However, our experimental data suggest that the higher-energy 2 PA band may have other contributions due to the mixing between the heavy-and the light-hole bands, which the effective mass model does not take into consideration.
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