Synthesis of red fluorescence peptide through azobenzene-containing β-peptide foldamer

Abstract

Different from numerous chromophores commonly exploited as fluorescent materials, examples of steadily fluorescent azobenzene compounds are limited. Attempts to increase and modulate the fluorescence performance of azobenzene compounds are quite recent and based on suppression of fast photo-isomerization. However, the utilization of azobenzene chromophores in application for fluorescent probes is still problematic due to the low luminescence efficiency compare to existing organic fluorescent materials. Improving azobenzene’s luminescence efficiency is one of the most important research purposes in this area. Moreover, unsubstituted azobenzene itself fluorescent has never been reported since the discovery of the isomerization of azobenzene in 1937. Here, we present a simple strategy to prepare efficient red fluorescent azobenzene containing β-peptide foldamer microdot by supramolecular self-assembly induced emission enhancement. The investigation of spectroscopic properties showed that fluorescence enhancement of cis-azobenzene under UV irradiation while trans azobenzene itself in the initial solution is negligible fluorescent. By self-assembly of cis-rich azobenzene peptide foldamer, we demonstrated peptide microdot exhibiting stable red fluorescence in vivo environment without photo- bleaching problem. The self-assembly strategy allowed us to achieve luminescence properties that could not be achieved from unsubstituted azobenzene so far. We anticipate this study provide a new insight in the design and fabrication of efficient fluorescent azobenzene chromophore based materials for broad fluorescent probes and biomedical applications.