Hierarchical Self-Assembly and Multidynamic Responsiveness of Fluorescent Dynamic Covalent Networks Forming Organogels

Abstract

Smart stimuli-responsive fluorescent materials are of interest in the context of sensing and imaging applications. In this project, we elaborated multi-dynamic fluorescent materials made of a tetraphenylethene fluorophore displaying aggregation-induced emission and short cysteine-rich C-hydrazide peptides. Specifically, we show that a hierarchical dynamic covalent self-assembly process, combining disulphide and acyl-hydrazone bonds formation operating simultaneously in a one-pot reaction, yields cage compounds at low concentration (2 mM) while soluble fluorescent dynamic covalent networks and even chemically cross-linked fluorescent organogels are formed at higher concentrations. The number of cysteine residues in the peptide sequence impacts directly the mechanical properties of the resulting organogels, Young moduli varying 2500-fold across the series. Those materials underpinned by a nanofibrillar network display multi-dynamic responsiveness following concentration changes, chemical triggers, as well as light irradiation, all of which enable their controlled degradation with concomitant changes in spectroscopic outputs -self-assembly enhancing fluorescence emission by ca. 100-fold and disassembly quenching fluorescence emission.

Quadruple Functionalization of a Tetraphenylethylene Aromatic Scaffold with Ynamides or Tetracyanobutadienes: Synthesis and Optical Properties

“…In both cases, a weak emission could be recorded from 550 to 1300 nm for tetra‐TCBD 4 (with a maximum at 760 nm), and from 650 to 1300 nm for mono‐TCBD 13 (with a maximum at 800 nm). These observations are in line with previous reports from our group about the solid‐state luminescence in the near‐infrared (NIR) range of TCBD connected to polyaromatic cores, [20,21] and, again, in stark contrast with the fluorescence emission of the starting TPE tetra‐aldehyde 9 which is centered around 520 nm [39–41] …”

“…The UV‐visible absorption spectra were recorded from solutions in dichloromethane (Figure 2). In contrast with the starting TPE tetra‐aldehyde 9 which exhibits a maximum of absorption of UV light at around 320 nm, [39–41] they both exhibit a broad band in the visible range (up to 600 nm), characteristics of TCBDs derived from ynamides linked to polyaromatic cores [20,21,43] . While the absorption coefficient at the maximum of this band for mono‐TCBD 13 is about 0.6×10 4 mol −1 .L.cm −1 , the one from tetra‐TCBD 4 is around 4‐fold this value at 2.8×10 4 mol −1 .L.cm −1 , which amounts to the difference in the number of TCBDs present in the molecule (1 for compound 13 vs. 4 for compound 4 ).…”

“…These conditions were then applied to the synthesis of the tetra-ynamide TPE 3. First, precursor 10 bearing four gemdibromovinylic functions was synthesized from the corresponding tetra-aldehyde 9 [39][40][41] in the presence of triphenylphosphine and tetrabromomethane in dichloromethane (53 % yield). Subsequently, compound 10 was reacted with methyltosylamide under the same Hsung's conditions as previously applied for 1.…”

“…These observations are in line with previous reports from our group about the solid-state luminescence in the near-infrared (NIR) range of TCBD connected to polyaromatic cores, [20,21] and, again, in stark contrast with the fluorescence emission of the starting TPE tetra-aldehyde 9 which is centered around 520 nm. [39][40][41]…”

Fluorescent Dynamic Covalent Polymers for DNA Complexation and Templated Assembly

“…Dynamic Covalent Chemistry (DCvC) encompasses a set of possible reactions enabling reversible covalent bond formation under thermodynamic control [ 1 ]. DCvC endows dynamic and adaptive properties which are now increasingly considered for designing self-healing, stimuli-responsive, and adaptive materials [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ] such as Dynamic Covalent Polymers (DCPs) [ 9 ]. Alongside their interest in materials science, DCPs also bear a strong potential in biological applications such as sensing, imaging, delivery, and drug discovery [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”