Recently, a great deal of research has been started on generating fairly strong photoluminescence from organic molecules without having any conjugated π-system or fluorophore. Discrete chromophores or auxochromophores termed as “subfluorophores” may undergo “space conjugation” via co-operative intramolecular conformation followed by intermolecular aggregation to generate fluorescence or sometimes phosphorescence emission. Polymeric materials are important in this regard as nonconjugated polymers self-assemble/aggregate in a moderately concentrated solution and also in the solid state, producing membranes, films, and so forth with good physical and mechanical properties. Therefore, promoting fluorescence in these commodity polymers is very much useful for sensing, organic light emitting diodes (OLED), and biological applications. In this perspective, we have discussed the aggregation-induced emission from four different types of architectures, for example, (i) dendrimers or hyperbranched polymers, (ii) entrapped polymeric micellar self-assembly, (iii) cluster formation, and (iv) stretching-induced aggregation, begining with the genesis of fluorescence from aggregation of propeller-shaped small organic molecules. The mechanism of induced fluorescence of polymers with subfluorophoric groups is also discussed from the theoretical calculations of the energy bands in the aggregated state. Also, an attempt has been made to highlight some useful applications in the sensing of surfactants, bacteria, cell imaging, drug delivery, gene delivery, OLED, and so forth.

Recently, there has been a growth of research on the nonconjugated polymer exhibiting fluorescence property and it would be exciting if fluorescence property is developed in zwitterionic polymers because of their good water solubility. Poly(vinylidene fluoride) (PVDF) grafted with poly(dimethyl amino ethyl methacrylate) (PDMAEMA) is fractionated and a highly water-soluble fraction (PVDM-1) is quaternized with 1,3-propane sultone, producing a zwitterionic polymer, PVDF-g-PDMAEMA-sultone (PVDMS). PVDM-1 shows the fluorescence property with very low quantum yield (1%) in water, but on quaternization, fluorescence quantum yield increases to 8%. Transmission electron microscopy results indicate that the PVDM-1 cast from water has vesicular morphology, whereas PVDMS exhibits aggregated vesicular morphology. The 1 H NMR spectra indicate the presence of 72 mol % DMAEMA in PVDM-1 wherein 66% of -NMe2 groups is quaternized upon postpolymerization modification. PVDM-1 exhibits absorption peaks at 210, 276, and 457 nm with a hump at 430 nm, whereas PVDMS exhibits two absorption peaks at 203 and 297 nm. PVDM-1 exhibits a broad emission peak at 534 nm, whereas PVDMS exhibits a sharp emission peak at 438 nm. An attempt has been made from density functional theory calculations to shed light on the origin of fluorescence in both PVDM-1 and in the zwitterionic PVDMS. The excitonic decay occurs from the lowest unoccupied molecular orbital (LUMO) of carbonyl group to the highest occupied molecular orbital (HOMO) of tertiary amine group for PVDM-1, whereas in PVDMS, the excitonic transition occurs from the LUMO situated over the quaternary ammonium group to the HOMO located on the electron-rich terminal sulfonate group.

Hierarchical graphene oxide-g-polyaniline nanocomposites with a controlled nanostructure of uniformly oriented onedimensional (1D) polyaniline (PANI) nanocylinders over twodimensional (2D) graphene oxide (GO) surfaces are synthesized. PANI chains are grown from GO surface attached oligoaniline units following a "grafting from" approach, via chemical oxidative polymerization in aqueous acidic medium. Detailed kinetic analysis of aniline polymerization, both in the presence of oligoaniline attached graphene oxide and an equivalent amount of graphene oxide only, is presented for better understanding of the effect of oligoanilines over heterogeneous surface catalysis. The developed method involves a generalized approach, which holds potential for applications on various nanosurfaces irrespective of their dimensionality or nature. Significant control over the polyaniline chain growth helps to retain the basic morphology of the template nanomaterials, which is conducive for having improved synergy between the components. The nanostructured materials show further organization to generate unique, highly porous three-dimensional (3D) microstructures. These are presumably generated via supramolecular organization by the in situ developed higher oligoaniline nucleates, followed by controlled growth of polyaniline chains from them. The morphology of the developed nano/microstructures under controlled condition is in sharp contrast with the equivalent nanocomposite synthesized without imposing the control. Nanocomposites containing supramolecularly organized macroporous, three-dimensional microstructures have shown remarkably improved specific capacitance as high as 965 F/g (1 A/g) compared to 442 F/g (1 A/g) for the noncovalently attached uncontrolled nanocomposite under similar conditions. A thorough characterization of the nanocomposites using various spectroscopy, electron microscopy, X-ray crystallography, X-ray photoelectron spectrocscopy, surface area analysis, and electrochemical analysis techniques are conducted. A probable mechanistic interpretation for the microstructure formation considering supramolecular organization of the in situ developed, graphene oxide surface attached platelet like aniline oligomers has been proposed.

A poly­(vinylidine fluoride) graft random copolymer of t-butyl aminoethyl methacrylate (tBAEMA) and oligo­(ethylene glycol) methyl ether methacrylate (OEGMA, Mn = 300) [PVDF-g-P­(tBAEMA–ran-OEGMA), PVBO] is synthesized by atom transfer radical polymerization (ATRP), and PVBO is fractionated to get a highly water-soluble fraction (PVBO-1) showing a reversible on/off fluorescence behavior with gradual increase and decrease in pH, respectively, achieving a maximum quantum yield of 0.18 at pH = 12. PVBO-1 dissolved in water shows large multimicellar aggregates (MMcA), but at pH 12, crumbling of larger aggregates to much smaller micelles occurs, forming nonconjugated polymer dots (NCPDs), as supported by transmission electron microscopy and dynamic light scattering study. The reversible fluorescence on/off behavior also occurs with the decrease and increase of temperature. Theoretical study indicates that, at high pH, most of the amino groups become neutral and exhibit a strong tendency to form aggregates from crowding of a large number of carbonyl and amine groups, minimizing the HOMO–LUMO gap, showing an absorption peak at the visible region, and generating aggregation-induced emission.

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Synthesis of different poly(vinylidene fluoride) (PVDF)-grafted amphiphilic random ter-/bicopolymers containing reactive poly(furfuryl methacrylate) or thermoresponsive poly(diethyleneglycol methyl ether methacrylate), and so forth as constituents was successfully carried out by atom transfer radical polymerization in homogeneous solution and thoroughly characterized. Postpolymerization modification of the graft copolymers (pendant furan rings) was subsequently carried out by the Diels−Alder reaction with maleimide to introduce imidodicarbonyl moieties capable of exerting affinity interaction with melamine or nucleobases. Membranes having surface-enriched polar/hydrophilic moieties and stimuli-dependent pore sizes were fabricated by breath f igure or immersionprecipitation techniques. The synthesized graft copolymeric membranes showed superior antifouling properties than similar pure PVDF membranes and also exhibited preferential immobilization of adenine/melamine over uracil from aqueous solution due to complementary supramolecular interactions. In a filtration experiment, the synthesized graft copolymeric membrane (100 mg) has shown ∼60% RNA immobilization from 5 mL of 5 μM aqueous solution.

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