Molecular Structure-Optical Property Relationship of Salicylidene Derivatives: A Study on the First-Order Hyperpolarizability

The first-order hyperpolarizability of pi-conjugated organic molecules is of particular interest for the fabrication of electro-optical modulators. Thus, we investigated the relationship between the molecular structure and the incoherent second-order nonlinear optical response (beta(HRS)) of four salicylidene derivatives (salophen, [Zn(salophen)(OH2)], 3,4-benzophen, [Zn(3,4-benzophen)(OH2)]) dissolved in DMSO. For that, we employed the Hyper-Rayleigh Scattering technique with picosecond pulse trains. Our experimental results pointed out dynamic beta(HRS) values between 32.0 +/- 4.8 x 10(-30) cm(5)/esu and 58.5 +/- 8.0 x 10(-30) cm(5)/esu at 1064 nm, depending on the molecular geometry of the salicylidene molecules. More specifically, the outcomes indicate a considerable increase of beta(HRS) magnitude (similar to 30%) when in the ligands are incorporated the Zn(II) ion. We ascribed such results to the rise of the planarity of the pi-conjugated backbone of the chromophores caused by the Zn(II). Furthermore, we observed an increase of similar to 50% in dynamic films when there is a replacement of one hydrogen atom (salophen molecule) by an acetophenone group (3,4-benzophen). This result is related to the increase of the effective pi-electron number and the higher charge transfer induced at the excited state. All these findings were interpreted and supported in the light of time-dependent density functional theory (DFT) calculations. Solvent effects were considered in the quantum chemical calculations using the integral equation formalism variant of the polarizable continuum model.

Automated summary

This study explored the relationship between molecular structure and incoherent second-order nonlinear optical response of four salicylidene derivatives dissolved in DMSO. The results indicated that changes in molecular geometry and the incorporation of Zn(II) ions can significantly impact the nonlinear optical response. Additionally, the increase in the effective pi-electron number and charge transfer induced at the excited state were found to influence the dynamic films' response.