Novel 4,40-Binaphthalimidyl derivatives with carboxyalkyl side chains: Synthesis, Aggregation-induced emission, Hydrogel and Cell imaging

The introduction of aryl groups and/or alkyl side chains to the periphery of a conjugated skeleton can modulate the pattern of molecular aggregation in solution and facilitate its aggregation-induced emission (AIE) performance. In this study, novel three compounds of 4,40-binaphthalimidyl derivatives (BNICn) were synthesized successfully in which two 1,8-naphthalimide (NI) units were connected by a rotatable single bond at their 4-sites, and two carboxyalkyl chains (number of carbon atoms in the carboxyalkyl chains (n) = 2, 6, and 11) were linked with the nitrogen atoms of NI. BNICn has weakly fluorescent in dilute solutions but become highly emissive in aggregate states. Interestingly, they exhibited carboxyalkyl-dependent AIE properties. The AIE performance of BNIC2 with the shortest carboxyalkyl chain is the strongest among those of the three compounds. The aggregation was also confirmed by the dynamic light scattering (DLS) tests. Moreover, the fluorescence intensities enhanced with the increasing viscosity of the solutions, verifying that the restriction of intramolecular motions (RIM) leads to the occurrence of AIE. Furthermore, the interactions such as rc-rc stacking of NI groups, and the intermolecular hydrogen-bonding of the carboxyl groups at the terminal of the side chains of BNICn was respectively verified by 1H NMR and FTIR. Thus, a possible self-assemble mode of BNICn is that the stacking NI segments of BNICn are located by the intermolecular hydrogen bonds of carboxyl groups at the terminal of the side chains of BNICn enacting an anchor-like role during aggregation process. For BNIC2with carboxymethyl group, the shortest spacer of methylene group resulted in more effectively restriction for the intramolecular vibration and rotation, leading to a more efficient AIE performance. Meanwhile, BNIC11 can form thermal-reversible fluorescence hydrogel with ethylenediamine as well as BNIC2 can be applied in cellular imaging. Thus, an effective strategy to achieve and adjust the AIE performance of NI derivatives is proposed. & COPY; 2023 Elsevier B.V. All rights reserved.