Entropy-Enthalpy Compensation in Solvent Geometry Regulated Supramolecular Polymerization of Luminescent Napthalimide via a Non-Cooperative, Isodesmic Mechanism.

Supramolecular polymers of π-conjugated systems are an important class of materials with fascinating functions and properties originated from the dynamic behavior and highly ordered molecular organizations. Here, a donor-π-acceptor based functionalized luminescent napthalene monoimide (NMI) undergoes J-type self-assembly by non-covalent interactions via a non-cooperative, isodesmic mechanism to form supramolecular 1D nanowire. The fundamental insights into the thermodynamics regulating the supramolecular polymerization were derived through the fitting of the isodesmic model to variable temperature UV/Vis data in linear (dodecane) and nonliner hydrocarbon (decalin) based solvents. This shows a significant role of entropy-enthalpy compensation in solvent geometry-regulated formation and stabilization of supramolecular polymer. Furthermore, we have quantitively estimated the influence of solvent geometry and found that NMI forms stronger self-assembly and spontaneous gel in linear hydrocarbon based solvent compared to nonliner one and thereby substantially increases the degree of polymerization in linear hydrocarbon solvent (dodecane). This is accredited to the effective influence of the linear hydrocarbon solvent molecules in the polymerization process by favourable van der waals interactions with the peripheral alkyl chains of the NMI monomers in contrast to unfavourable interaction of nonliner hydrocarbon solvent due to geometry mismatch.

Anion-assisted supramolecular polymerization of luminescent organic π-conjugated chromophores in a moderately polar solvent: tunable nanostructures and their corresponding effects on electronic properties.

Supramolecular polymers of π-conjugated organic chromophores have emerged as promising candidates in organic electronics because of their dynamic and highly ordered molecular organization. Herein, we demonstrate the formation of luminescent, highly conducting supramolecular polymers of a functionalized naphthalimide π-chromophore-based organic semiconductor in a moderately polar organic solvent (tetrahydrofuran) by overcoming solute-solvent H-bonding via assistance from fluoride anions. The polymerization is exclusively guided by the synergistic effects of cascade H-bonding (F-⋯H-N- of primary amines, followed by -CO⋯H-N- of amides), π-π stacking and hydrophobic interactions. An increasing molar equivalent of anions leads to a morphology transition from 1D nanowires to 2D nanosheets via nanotubes and nanorings, but above a particular threshold of the same anion, depolymerization-mediated disruption of long-range order and formation of non-luminescent spherical particles was observed. Such significant impacts of anions in supramolecular polymerization-depolymerization were utilized in modulating the electronic properties of this naphthalimide-based organic semiconductor.

Bioderived Lipoic Acid-Based Dynamic Covalent Nanonetworks of Poly(disulfide)s: Enhanced Encapsulation Stability and Cancer Cell-Selective Delivery of Drugs.

Dynamic covalent poly(disulfide)-based cross-linked nanoaggregates, termed nanonetworks (NNs), endowed with pH- and redox-responsive degradation features have been fabricated for stable noncovalent encapsulation and triggered cargo release in a controlled fashion. A bioderived lipoic acid-based Gemini surfactant-like amphiphilic molecule was synthesized for the preparation of nanoaggregates. It self-assembles by a entropy-driven self-assembly process in aqueous milieu. To further stabilize the self-assembled nanostructure, the core was cross-linked by ring-opening disulfide exchange polymerization (RODEP) of 1,2-dithiolane rings situated inside the core of the nanoaggregates. The cross-linked nanoaggregates, i.e., nanonetwork, are found to be stable in the presence of blood serum, and also, they maintain the self-assembled structure even below the critical aggregation concentration (CAC) as probed by dynamic light scattering (DLS) experiments. The nanonetwork showed almost 50% reduction in guest leakage compared to that of the nanoaggregates as shown by the release profile in the absence of stimuli, suggesting high encapsulation stability as evidenced by the fluorescence resonance energy transfer (FRET) experiment. The decross-linking of the nanonetwork occurs in response to redox and pH stimuli due to disulfide reduction and ß-thioester hydrolysis, respectively, thus empowering disassembly-mediated controlled cargo release up to ∼87% for 55 h of incubation. The biological evaluation of the doxorubicin (DOX)-loaded nanonetwork revealed environment-specific surface charge modulation-mediated cancer cell-selective cellular uptake and cytotoxicity. The benign nature of the nanonetwork toward normal cells makes the system very promising in targeted drug delivery applications. Thus, the ease of synthesis, nanonetwork fabrication reproducibility, robust stability, triggered drug release in a controlled fashion, and cell-selective cytotoxicity behavior, we believe, will make the system a potential candidate in the development of robust materials for chemotherapeutic applications.