Engineering Single Component Luminogens to Multicomponent Charge‐transfer Co‐crystal Substrate as New Frontiers for Sensitive SERS Detection

Organic charge‐transfer (CT) co‐crystals have demonstrated remarkable physical properties and have found applications in numerous fields. Yet their utility as a Surface‐Enhanced Raman Spectroscopy (SERS) substrate, a powerful and versatile analytical tool, has never been explored. Herein, three twisted molecular donors are synthesized, that exhibit well‐controlled switchable optical properties including aggregation‐induced emission (AIE), mechanochromic luminescence (MCL), and color‐specific polymorphism. Rapid production of charge‐transfer co‐crystals is also established with a π‐acceptor TCNQ and utilized conceptually as a SERS substrate for methylene blue (MB) detection, exhibiting a very high enhancement factor of 109 and limit of detection of 10−13 m, respectively, due to the presence of low‐lying excited state, exhibit an 80% CT character, originating from the HOMO of the co‐crystal and interacting with the LUMO of the MB molecule. This approach using CT co‐crystals as a SERS substrate presents newer frontiers that require minuscule levels of rapid detection and impact allied areas, helping us understand and optimize the fascinating properties of such multicomponent materials for newer technologies.