A fluorescent alternative copolymer combined energy transfer and charge transfer with large and tunable Pseudo-Stokes shift

Fluorescent materials with a large enough Stokes shift (>100 nm) have widely prospect in light conversion agricultural film, cell-imaging, chemosensory and so on. However, most of traditional fluorescent dyes displayed small Stokes shifts which severely limited their application. In this paper, a side-chain alternative copolymer named P(DMPNI-alt-TPE) was developed, in which the two fluorophores were next to each other: the AIE-active tetraphenylethene (TPE) acted as energy donor, while naphthalimide derivative (DMPNI) with intramolecular charge transfer (ICT) character as energy acceptor. Attributed to this unique structure, the copolymer combined efficient dark/fluorescence resonance energy transfer (DRET/FRET) and polarity-sensitivity. And therefore it showed impressive large pseudo-Stokes Shift up to 304 nm and 302 nm in solution and aggregative state respectively. Interestingly, this copolymer exhibited a V-shaped fluorescence variation curve in a series of THF solutions with increasing fraction of water. Moreover, P(DMPNI-alt-TPE) emitted different color fluorescence in various solvents upon UV light, so that its pseudo-Stokes shift was not only large but also tunable, and the changing range was from 262 to 304 nm. Lastly, the potential possibility of P(DMPNI-alt-TPE) as light conversion agricultural film was investigated. This research provided a new approach for the development of fluorescence materials with large and tunable Stokes shift.

Automated summary

This study developed a side-chain alternative copolymer P(DMPNI-alt-TPE) with large Stokes shift and tunable properties, showing potential prospects in the application of fluorescence materials.