The flexibility of side chains for adjusting the emission of 4-aryl-1,8-naphthalimides in aggregation: Spectral study and cell imaging

Abstract

The fabrication of a red to near-infrared emissive molecules in aggregated states is very important for bioimaging. 4-Aryl-1,8-naphthalimides(ArNIs) are potential aggregation-induced emissive and aggregated-induced enhanced emissive molecules. Herein, we designed and synthesized three ArNIs derivatives (NITPA1 ~ 3). All three compounds exhibit aggregation-induced emission phenomenon. The photophysical properties of these compounds were investigated that all compounds exhibited more than 250 nm red-shift (from ~ 500 nm to 750 nm) implied their effective intramolecular charge transfer. Moreover, all three compounds showed red emission in aqueous solutions with the emission bands tailing to about 800 nm. The fluorescent spectra of these compounds indicated that the alkyl chains always produced band shift and color change in the increasing fractions of water. Three compounds also exhibited the obvious solid emissions with different fluorescent colors (NITPA1: green, 524 nm; NITPA2: orange, 565 nm, and NITPA3: red, 610 nm). Thus, changing the end group of the side chains could be an alternative way to tune their fluorescent behaviors in different aggregated states. This work provides a new strategy to design AIE-active and fluorescent solid materials. At last, a cell imaging experiment was performed for evaluating the bioimaging capabilities of these compounds. Among them, NITPA1 shows the best cell-staining ability.