Synthesis, Structural Characterization, Hirshfeld Surface Analysis, and Evaluation of Nonlinear Optical Properties of Novel Cocrystal of Acridine with 2,4-Dihydroxybenzaldehyde

A cocrystal of acridine with 2,4-dihydroxybenzaldehyde (2:1 stoichiometric ratio) was synthesized, spectrally and structurally characterized using TG, DSC, ATR-FTIR and Single-Crystal XRD methods and Hirshfeld surface analysis, and its nonlinear optical properties were investigated by DFT at the B3LYP/6-311++Glevel. The obtained compound crystallizes in the noncentrosymmetric <i>P</i>2₁ monoclinic space group, with two molecules of acridine and one molecule of 2,4-dihydroxybenzaldehyde in the asymmetric unit. The strong O_(aldehyde)-H⋯N_(acridine) and weak C_(aldehyde)-H⋯O_(aldehyde) and C_(aldehyde)-H⋯O_(aldehyde) hydrogen bonds, as well as π_(acridine)-π_(acridine) and C_(acridine)-H⋯π_(aldehyde) interactions, are present in the crystal lattice of the title compound. The calculated energy gap (ΔE) between the HOMO-LUMO surfaces shows charge transfer interactions due to the π-π* transitions among the molecules. The calculated first and second hyperpolarizability values indicate that obtained cocrystal is a promising candidate for nonlinear optical applications.