Interpreting the First-Order Electronic Hyperpolarizability for a Series of Octupolar Push–Pull Triarylamine Molecules Containing Trifluoromethyl

Abstract

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).

Photoinduced Intramolecular Charge Transfer and Hyperpolarizability Coefficient in Push‐Pull Pyridinium Salts with Increasing Strength of the Acceptor Group

“…In fact, the β 0 value of 330×10 −30 esu −1 cm 5 derived for A doubles or triples when the N ‐methyl substituent is replaced by the N ‐pyrimidin‐2yl ( B ) or N ‐dinitrophenyl ( C ), respectively (Table ). However, the β 0 values estimated for the present investigated salts resulted high if compared with analogous pyridinium‐based chromophores, and generally comparable with those of systems considered actual NLO materials ,. The significant quadratic NLO activity exhibited by A and particularly by B and C , can be explained taking into account the presence of the very strong electron‐donor piperidine and the positively charged N ‐pyrimidin‐2yl‐ and N ‐dinitrophenyl‐pyridinium as strong electron‐acceptors connected by electron‐rich diene and dithiophenes chain.…”

“…This method allowed the difference between the excited and ground state dipole moment (Δμ) as well as the dynamic (β CT ) and static (β 0 ) hyperpolarizability coefficients to be derived. The β values have been found sizable and comparable to those of systems considered de facto NLO materials ,. The comparison between the A properties and those previously retrieved for the analogous ortho‐substituted salt (namely 1‐methyl‐2‐{( E )‐2‐[5′‐(piperidin‐1‐yl)‐2,2′‐bithiophen‐5‐yl]ethenyl}pyridinium iodide) by the same solvatochromic study, evidenced lower β values for the latter (halved β CT and β 0 reduced by ca .…”

New Styryl Phenanthroline Derivatives as Model D−π−A−π−D Materials for Non‐Linear Optics

“…The reason for this may lie in the fact that the computations are only able to define a minimum on the potential energy surface which is close to the FC state (LE), but cannot describe the relaxation to another minimum that has instead been identified as the highly polar ICT state. The β CT values thus derived for X n in ACN are rather high and comparable to, and not far from those of organic compounds considered NLO materials. In particular, the value obtained for X2 , almost one order of magnitude smaller than those found for the other compounds of the series, is presumably underestimated because of the superimposition in the UV‐Vis spectrum of two absorption bands associated with two different transitions, so that a proper integration of the band is not possible.…”

“…The notable fluorosolvatochromism of the present compounds, producing large Stokes shifts that increase with solvent polarity, allowed the hyperpolarizability coefficient to be estimated. Both the hyperpolarizability coefficients (β) and the TPA cross‐section (δ), evaluated by means of Two photon excited fluorescence, resulted rather large and comparable to those of other organic compounds considered NLO materials ,,. They exhibited the same trend that well matches that of the push‐pull character granted by the electron‐donor capability of the different substituents: X3 < X5 < X4 , with the latter showing the highest value.…”

The structural and photophysical properties of multibranched derivatives with curved conjugated aromatic cores

“…Among them, a well known case is octupolar molecule (as shown in Scheme 1) with three fold symmetry which have been demonstrated to be good NLO candidates [11][12][13][14][15] .…”