Tunable Self-Assembly and Aggregation-Induced Emission Characteristics of Triarylboron-Decorated Naphthalimides

Understanding the structure-property and structure-morphology correlations of organic luminescent materials is essential in order to employ such materials for desired applications. In this regard, we prepared a library of novel triarylboron-tethered N-boryl-1,8-naphthalimides (TAB-NPIs) 1-6 with variations in their steric and electronic factors. Compounds 1-6 are weakly luminescent in molecularly dispersed state; however, they are strongly luminescent in the aggregated state (THF-H₂O mixture). The presence of sterically hindered triarylboryl units in 1-6 endowed these molecules with aggregation-induced emission (AIE) characteristics by preventing cofacial arrangements of NPI moieties, as shown by the supramolecular interactions in the crystal lattice. These structural features preclude excimer formation which can be detrimental to the radiative process in these molecules. Promisingly, these compounds undergo self-assembly and form interesting morphologies such as sheets (1), fibers (2), tubes (3), vesicles (4), flowers (5), and porous films (6). These types of morphologies are rarely observed in purely organic materials; evidently, the morphology of these compounds strongly depends on their molecular conformations and steric and electronic factors.