Novel cocrystals of 18-crown-6 (18C6) with 5-nitroisophthalic acid (5NIPA) have been prepared by reaction in a solution of CH3OH–H2O (2:3, v/v) and C2H5OH–H2O (2:3, v/v) systems. The cocrystals 18-crown-6.5-nitroisophthalic acid. CH3OH.2(H2O) (I) and 18-crown-6.5-nitroisophthalic acid.3(H2O) (II) have been characterized by X-ray diffraction and constructed supramolecular assembly is thoroughly investigated. CH3OH incorporation inducing centrosymmetric crystallization and acentric crystal packed supramolecular construction in presence of ethanol are the highlights of the study. Intermolecular interactions are quantified by Hirshfeld surface analysis. First-order molecular hyperpolarizability estimated by theoretical calculations indicate a significant microlevel nonlinearity in both cases and Z-scan studies suggest a promising third-order nonlinear optical behaviour. Supramolecular assembly afford multiple strong O–H ….O hydrogen bonds creating a facile atmosphere for optical nonlinearity and mainly these O ….O hydrogen bonds stabilize the structure. © 2019 Elsevier B.V.