Molecular-Level Manipulation of the Topological Structures in Clamparene-Based Charge-Transfer Co-Crystals and Their Selective Recognition of Xylene Isomers

Organic cocrystals represent a cutting-edge strategy for fabricating high-performance organic functional materials, increasingly establishing their significance in materials science. This study investigates the influence of alkyl chain length modulation on the structure and vapochromic response properties by synthesizing two charge-transfer (CT) cocrystals composed of clamparene (CLP) and naphthalenediimide (NDI) derivative guests with varying alkyl chain lengths. Structural characterization reveals significant differences in the resulting materials, primarily due to variations in molecular packing arrangements induced by the alkyl chain lengths (C8 and C4), thus providing a unique platform for studying structure–property relationships. Solid-state characterization indicates that NDI8@CLPα exhibits a highly selective vapochromic response to para-xylene vapor, whereas NDI4@CLPα shows no discernible response. This result elucidates the regulatory role of alkyl chain length on intermolecular π–π stacking modes and, consequently, on the performance of the two CT cocrystals. This finding introduces a new dimension of structural control for the precise design of stimuli-responsive materials, particularly emphasizing the critical length requirement of alkyl chains in constructing such materials and offering significant guiding implications for the field of chemical sensors.