Spectroscopic and nonlinear optical investigations of biscinnamyl-sulfone derivatives: Computational and experimental...

Novel geometrically asymmetric biscinnamyl-sulfone compounds (6a-c) with donor-π-conjugated spacer-acceptor functionality were successfully synthesized. This was achieved by coupling cinnamaldehyde precursors with 3,3'-diaminodiphenyl sulfone in dry organic solvents, resulting in high yields. Several spectroscopic techniques were employed to identify the derivatives. The absorption spectra of these compounds exhibited broad bands that spanned up to 120 nm, which can be attributed to their extended conjugation systems. In order to explore the electronic transitions of these materials, Time-Dependent Density-Functional Theory (TD-DFT) with EIFPCM solvation mode was utilized. We computationally investigated the static nonlinear optical (NLO) parameters, including dipole moments (μ), polarizability (α), anisotropic polarizability (Δα), first-order hyperpolarization (β), and second-order hyperpolarization (γ). Although the new structures possess different functional groups, they displayed similar electronic potentials when their molecular electrostatic potentials were plotted. These potentials are crucial in stabilizing the molecules in crystal systems through noncovalent forces such as C-H⋯π stacking and hydrogen bonding. They also provide insights into the electronic assessments and energetics of these individual forces. By estimating the frontier orbitals, we gained an understanding of the intramolecular charge transfer in the compounds. Energy gap values were determined using the orbitals of density of states method and experimentally via the Tauc method. The computational and experimental results were in good agreement. Lastly, we examined the influence of different protic and aprotic solvents on the absorption bands of compound 6b, as an example. This compound showed a significant bathochromic shift of 41 nm upon changing the solvent from acetic acid to dimethyl sulfoxide.