Functional group engineering in naphthalimides: a conceptual insight to fine-tune the supramolecular self-assembly and condensed state luminescence

Abstract

Engineering well-defined supramolecular fluorescent nano-architectures based on organic conjugated small molecules has been an essential scientific challenge. Herein, a library of sixteen naphthalimide congeners (1–15 and HNI) has been strategically designed that unveils a conceptual insight into the functional group controlled condensed state emission and aggregation-induced enhanced emission (AIEE) in conventional strong aggregation-caused quenching (ACQ) active fluorophores. Along with the regulation of ACQ-to-AIEE transformation and tailoring of the condensed state emission, a simple yet potential design strategy of functional group engineering has been established for the first time to spontaneously generate and systematically tailor the supramolecular self-assembly of organic small molecules into highly defined nano-architectures. Single-crystal XRD analysis of six congeners revealed that, unlike the well-established electronic contribution of the functional groups in the molecularly dispersed state, the condensed state photophysical and morphological properties are dictated by the distinct intermolecular π–π stacking interaction of the planar aromatic core. This work demonstrates an unconventional influence of the functional motif in the condensed state that could emerge as a promising route to build a fluorescent supramolecular nanoassembly from non-fluorescent conjugated molecules for a variety of future applications.