Position and conjugation–dependent aggregation–induced emission enhancement properties of naphthalimide–tetraphenylethylene conjugates

Abstract

A series of position and conjugation–dependent donor–acceptor naphthalimide–tetraphenylethylene isomeric conjugates (NTPEs 1–6), possessing single–bond (C–C), vinyl linkage, and acetylene linkage between naphthalimide and tetraphenylethylene moieties, were designed and synthesized. NTPEs 1–6 were fully characterized by 1H NMR, 13C NMR, and mass spectroscopy. The effects of the position and conjugation in NTPEs 1–6 on the absorption, fluorescence, and aggregation–induced emission enhancement were explored. Among the NTPEs 1–6, the 4–substituted NTPEs show the most prominent electronic communication. Furthermore, the 3–substituted NTPEs and 4–substituted NTPEs with single–bond linkage exhibit aggregation–induced emission enhancement, whereas 4–substituted NTPEs with vinyl linkage, and acetylene linkage show small aggregation–caused quenching. The NTPEs 1–3 and 5 show enhanced fluorescence and long fluorescent lifetimes in aggregated state, exhibiting aggregation induced emission. The nanoaggregates of NTPEs 1–6 formed in tetrahydrofuran/water (1:9, v/v) solutions are observed by scanning electron microscopy (SEM), fluorescence microscopy, and dynamic light scattering (DLS).