Novel Push−Pull Phthalocyanines as Targets for Second-Order Nonlinear Applications

Abstract

The second harmonic generation (SHG) hyperpolarizabilities of a family of peripherally substituted pushpull phthalocyanines 1, 2, and 3, having an ethynediyl subunit in the linking bridge between the acceptor and donor moieties, have been measured. Electric field induced second harmonic (EFISH) generation experiments at 1.064 and 1.900 µm and hyper-Rayleigh scattering (HRS) experiments at 1.064 µm have been carried out.The quadratic hyperpolarizabilities values derived from these experiments are quite significant and superior to those found for similar push-pull compounds lacking of a triple C-bond in the donor-acceptor path. The main electronic parameters of the three compounds (electric dipole moments, orbital electronic distributions, and optical transition moments) have been calculated using the ZINDO/S method for molecular geometries that have been optimized through the PM3 method. Excellent agreement with spectroscopic data has been achieved. The SHG results have been analyzed through a 3-level model associated to the ground level and two split levels responsible for the Q-band, assuming either strict (for compound 2) or approximate (for compounds 1 and 3) C 2V planar symmetry. The parameters used in the model were those obtained from the electronic calculations. For molecule 2, both the theoretical diagonal and off-diagonal elements of the beta tensor, as well as β EFISH and β HRS , have been determined. Good agreement with the experimental HRS values is obtained, whereas EFISH values considerably differ from those obtained from the simple expression for γ EFISH ignoring the electronic contributions.

Structural Modulation of the Dipolar−Octupolar Contributions to the NLO Response in Subphthalocyanines

“…It is important to notice the influence of nondiagonal components of the dipolar transition moment between excited states: µ 12 . 27 The dispersion factors D are given by Those expressions are of great relevance since they allow the evaluation of the dispersive contribution to the signal when the harmonic wavelength is close to the linear absorption wavelength. To compare with finite field calculations, which do not include dispersion, the SOS method was also extrapolated to ω ) 0.…”

Nonlinear Optical Properties of Porphyrins

“…Maya et al measured the SHG hyperpolarizabilities of a family of peripherally substituted push-pull phthalocyanines 9, 10, and 11. [21] These systems contain an ethynyl subunit in the bridge linking the acceptor and donor moieties. The quadratic hyperpolarizabilities values derived from EFISH (1064 and 1907 nm) and HRS experiments (at 1064 nm) were quite significant and superior to those found for similar push-pull compounds lacking a triple C-C bond in the donor-acceptor path.…”

Theoretical nonlinear optics equivalence between mesoionic and polyenic bridges in push-pull compounds

“…The calculated β(0) = 387x10 -30 esu, and it would be necessary more than ten double bonds in a polyenic bridge, since the higher calculated β(0) for the compound with ten double bonds is 271x10 -30 esu. For the system 1,3-dithiolium-5-tiolates (a, b and c = S) with the groups D = p-C 6 H 4 -N(Me) 2 and A = N',N-diethylthyobarbituric, the calculated β(0) is 174x10 -30 esu, while the corresponding similar β(0) value, for a polyene system with seven dienic units is β(0) = 167x10 -30 esu. In order to answer our initial question, we can point out that, in average, considering our highest calculated β(0) for the OOS ring, it is necessary for a polyenic bridge 190 161 321 198 182 299 2 271 191 100 245 181 377 224 224 387 3 205 134 9 5 180 176 250 187 178 265 4 220 150 142 206 207 290 203 202 299 5 152 102 9 7 158 148 172 156 163 185 6 102 8 2 6 9 122 113 120 121 128 128 Notation: The entries are related to groups A and D in Figure 1.…”

“…The interest in organic materials for nonlinear optics has been stimulated by the expectation of lower cost, faster optical response, higher versatility, possibility of tuning the structure in terms of their nonlinear optical properties, and nonlinear optics susceptibilities comparable or superior to conventional materials. [1][2][3][4][5][6] In general, the strategy adopted to intensify the nonlinear optics properties of organic compounds of the type electron acceptor -bridge -electron donor, A-bridge-D, consists in varying the electronic asymmetry and the length of conjugated backbone between the electron acceptor (A) and electron donor (D) groups. Marder et al 7 synthesized a series of push-pull compounds with polyenic bridges with different A and D groups (Figure 1).…”