Solvent Geometry Regulated J- and H-Type Aggregates of Photoswitchable Organogelator: Phase-Selective Thixotropic Gelation and Oil Spill Recovery.

We demonstrate supramolecular polymerization and formation of 1D nanofiber of azobenzene based organogelator (AZO-4) in cyclic hydrocarbon solvents (toluene and methylcyclohexane). The AZO-4 exhibits J- and H-type aggregates in toluene: MCH (9 : 1) and MCH: toluene (9 : 1) respectively. The type of aggregate was governed by the geometry of the solvents used in the self-assembly process. The J-type aggregates with high thermal stability in toluene is due to the enhanced interaction of AZO-4 π- surface with the toluene π-surface, whereas H-aggregate with moderate thermal stability in MCH was due to the interruption of the cyclic hydrocarbon in van der Waals interactions of peripheral chains of AZO-4 molecule. The light induced reversible photoisomerization is observed for both J- and H-aggregates. The macroscopic property revealed spontaneous and strong gelation in toluene preferably due to the strong interactions of the AZO-4 nanofibers with the toluene solvent molecules compared to the MCH. The rheological measurements revealed thixotropic nature of the gels by step-strain experiments at room temperature. The thermodynamic parameter (ΔHm) of gel-to-sol transition was determined for all the gels to get more insight into the gelation property. Furthermore, the phase selective gelation property was extended to the oil spill recovery application using diesel/water and petrol/water mixture.

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.