Unexpected fluorescence from polymers containing dithio/amino-succinimides

Abstract

Fluorescent polymers without conventional fluorescent units are attracting extensive interest because of their excellent biocompatibility. Succinimides are generally known as common fluorescence quenchers of proteins due to some degree of electron transfer between the excited state and the quencher. In this work, we observed unexpected fluorescence from succinimide-containing polymers. We synthesized a series of succinimides and found that 2,3-dithio-succinimide and 2-amino-succinimide were fluorescent, presenting solvent-dependent emission. This study is the first to report that nonfluorescent succinimides become fluorescent only by thiol and amine group substitutions, without employing any fluorescent units. The unusual fluorescence of dithio/amino-succinimides resulted from the spatial separation of HOMO and LUMO based on density functional theory calculations. Compared with monomers, polymers containing 2-amino-succinimide exhibited substantial fluorescence enhancement (maximum of ∼200fold) because of the isolation effect, in which nonradiative decay among succinimide fluorophores was significantly suppressed.

Nonconventional Fluorescent Polynorbornenes Bearing Aminosuccinimide Side Groups

“…However, nonfluorescent succinimides become emissive simply by amine moiety substitution without the introduction of any conventional fluorescent units. Yan et al reported that the fluorescence of aminosuccinimide comes from succinimide group rather than secondary amine moiety, and the fluorescence is attributed to the electron transfer from the nitrogen atom in the excited state toward the carbonyl group where nitrogen atom is an electron donor and the carbonyl group is an electron acceptor.…”

“…Meanwhile, Baker and Caddick along with other groups extensively investigated the substitution reaction between dibromomaleimide and thiols and used this sort of native disulfide bridging protocol to control polymer topology and fabricate functional polymer materials . The fluorescence of dithio/aminosuccinimides and corresponding copolymers was demonstrated by Yan et al for the first time . Later on, the same group illustrated a simple approach to simultaneously integrate amides and aliphatic imides into polymer backbones and construct fluorescent poly(amide‐imide)s with linear and hyperbranched topologies .…”

One‐pot synthesis of soluble and fluorescent aliphatic hyperbranched poly(amide‐imide) with solvent‐dependent emission

“…The Michael addition of a primary amine and a maleimide generates an aminosuccinimide fluorophore . Meanwhile, a thiolactone is susceptive to ring‐opening reaction in the presence of a primary amine, yielding a peptide bond and release a quantitative thiol .…”

Robust Organoalkoxysilanes as Red Unconventional Fluorescent Platform

“…[ 6 ] Recently, unconventional fluorophores, which do not contain any of the conjugated systems in their structures but still show visible fluorescent emission, have attracted great attention due to their excellent biocompatibility, processability, and facile availability. [ 7–9 ] Based on these advantages, the unconventional fluorophores may be suitable for biological applications. However, the application of unconventional fluorophores to the bioscience field is still under restrictions for the deficiency of efficient design strategies toward the unconventional fluorophores based fluorescent probes.…”