Novel side-chain alternative copolymer combined FRET and DRET with large pseudo-Stokes shift and polarity-sensitive fluorescence behavior

Abstract

A novel alternative copolymer incorporating tetraphenylethene (TPE) and naphthalimide (NI) into styrene and maleic anhydride as side chains was designed and synthesized. Attributed to the TPE units acting both as emissive donor in the aggregation state and dark donor in solution, this copolymer exhibited fluorescence resonance energy transfer (FRET) and dark resonance energy transfer (DRET) processes from TPE to NI, so it remained emissive whether in solution or aggregation state, and the fluorescence intensity of NI was increased obviously compared to when it was excited directly without energy transfer. Additionally, the alternative copolymer displayed an impressive pseudo-Stokes shift as large as 215 nm in the aggregation state, which was larger than those of all other reported systems’ combined FRET and DRET. Lastly, we found that this alternative copolymer exhibited interesting polarity-sensitive fluorescence behaviors in different polarity environments, and these behaviors were considered to be the result of the combined effects of polarity-sensitivity, energy transfer and solubility.