Structurally Tunable pH-Responsive Luminescent Assemblies from Halogen Bonded Supra-π-amphiphiles

Abstract

Supra-amphiphiles constituted of noncovalent bonds have emerged as attractive systems for fabrication of stimuli-responsive self-assembled nanostructures. A unique supramolecular strategy utilizing halogen (X)-bonding interaction has been demonstrated for constructing emissive supra-π-amphiphiles in water from a hydrophobic pyridyl functionalized naphthalene monoimide (NMI-Py) based X-bond acceptor and hydrophilic iodotetrafluorophenyl functionalized polyethylene glycol (PEG-I) or triethylene glycol (TEG-I) based X-bond donors, while their luminescent higher ordered assemblies were governed by orthogonal dipole−dipole interaction and π-stacking of the NMI-Py fluorophore as probed by SCXRD and DFT calculations. Control molecules lacking iodotetrafluorophenyl moiety at the polyethylene glycol chain end failed to create any defined morphology from the NMI-Py, suggesting X-bonding is prerequisite for the nanostructure formation. Variation in the chain length of the X-bond donors leads to different morphologies (fiber vs vesicle) for PEG-I and TEG-I. Acid triggered denaturing of the X-bonds caused pH responsive disassembly of the thermally robust nanostructures. This strategy paves the way for facile fabrication of structurally diverse smart and adaptive luminescent functional materials with tunable morphology.

Crystallization‐Driven Controlled Two‐Dimensional (2D) Assemblies from Chromophore‐Appended Poly(L‐lactide)s: Highly Efficient Energy Transfer on a 2D Surface

“…Solvent‐dependent absorption studies (Figure 4c) revealed ≈10 nm blue‐shift [15] in the absorption maxima (λ max =404 nm) in iPrOH compared to that in CHCl 3 (λ max =414 nm), indicating similar H‐type aggregation of the NMI‐dye on the surface of the 2D crystals. PL studies showed a slight reduction in the emission intensity with emission maxima (λ em ) at ≈520 nm in iPrOH (Figure 4c) compared to the monomeric dye in CHCl 3 owing to the known aggregation caused quenching effect of this dye [15c] . Similar to MC‐P1, no visible changes in the absorption and emission spectra, and platelet size and shape (Figure S13) were noted for a 4‐day aged solution of NMI‐P1, suggesting identical colloidal stability of its 2D crystals.…”

Recent Developments in Polymeric Assemblies and Functional Materials by Halogen Bonding

“…Water resistant halogen bonds may be the future of biomimetic materials design. Notably, many halogen bond acceptors are nitrogenous bases which confers pH responsiveness to the self‐assembled materials [100–101] . If coupled with suitable donor motifs, they can be explored for finding applicability in sustained and targeted drug delivery.…”

“…Needless to say that this applicability can pave the way for future design of self‐assembled biosensors for recognizing various biological processes and responding to different biological analytes [129] . Recent studies have demonstrated halogen bonding to be an extremely powerful tool for surface functionalization in aqueous medium [100–101] . Thus, future studies on surface decoration of macromolecules with functional halogen bond partners, responsive to biological targets will be extremely crucial.…”

“…General applicability of this strategy was tested by replacing BTA‐Py with a pyridyl‐functionalized naphthalene monoimide ( NMI‐Py ) acceptor, using the same donor moieties to create emissive supramolecular polymers in water (Figure 20C) [101] . The halogen bonded co‐assembly with TEG‐1 and PEG‐1 resulted in thermally robust green emitting vesicle and fibrillar morphology, respectively, with unprecedented high stability and similar acid‐responsive disassembly features.…”

Halogen bonding in polymer science: towards new smart materials

“…Subsequently, the variation of the XB-acceptor towards a pyridyl functionalized naphthalene monoimide (NMI-Py) with one acceptor moiety per molecule led to fibers upon complexation with PEG-1, whereas TEG-1 resulted in vesicles. 40 …”