Higher-order super-helical structures derived from biological molecules are known to evolve through opposite coiling of the initial helical fibers, as seen in collagen protein. A similar phenomenon is observed in a π-system self-assembly of chiral oligo(phenyleneethylene) derivatives (S)-1 and (R)-1 that explains the unequal formation of both left- and right-handed helices from molecule having a specific chiral center. Concentration- and temperature-dependent circular dichroism (CD) and UV/Vis spectroscopic studies revealed that the initial formation of helical aggregates is in accordance with the molecular chirality. At the next level of hierarchical self-assembly, coiling of the fibers occurs with opposite handedness, thereby superseding the command of the molecular chirality. This was confirmed by solvent-dependent decoiling of super-helical structures and concentration-dependent morphological analysis.

Metrics & MoreArticle RecommendationsCONSPECTUS: Molecules and materials derived from selfassembled extended π-systems have strong and reversible optical properties, which can be modulated with external stimuli such as temperature, mechanical stress, ions, the polarity of the medium, and so on. In many cases, absorption and emission responses of self-assembled supramolecular π-systems are manifested several times higher when compared with the individual molecular building blocks. These properties of molecular assemblies encourage scientists to have a deeper understanding of their design to explore them for suitable optoelectronic applications. Therefore, it is important to bring in highly responsive optical features in π-systems, for which it is necessary to modify their structures by varying the conjugation length and by introducing donor−acceptor functional groups. Using noncovalent forces, πsystems can be put together to form assemblies of different shapes and sizes with varied optical band gaps through controlling intermolecular electronic interactions. In addition, using directional forces, it is possible to bring anisotropy to the self-assembled nanostructures, facilitating efficient exciton migration, resulting in the modulation of optical and electron-transport properties.In this Account, we mainly summarize our findings with optically tunable self-assemblies of extended π-systems such as pphenylenevinylenes (PVs), p-phenyleneethynylenes (PEs), and diketopyrrolopyrroles (DPPs) as different stimuli-responsive platforms to develop sensors and security materials. We start with how PV self-assemblies and their coassemblies with appropriate electron-deficient systems can be used for the sensing of analytes in contact mode or in the vapor phase. For example, whereas the PV having electron-deficient terminal groups has high sensitivity toward trinitrotoluene (TNT) in contact mode, the supercoiled fibers formed by the coassembly of self-sorted stacks of C 3 -symmetrical PV and C 3 -symmetrical electron-deficient perylene bisimide are capable of sensing vapors of nitrobenzene and o-toluidine. The power of different functional groups in combination with PVs has been further illustrated by attaching CO 2 -sensitive tertiary amine moieties to a cyano-substituted PV, which allowed the bimodal detection of CO 2 using fluorescence and Raman spectroscopy. Interestingly, the functionalization of PVs with terminal amide groups and chiral alkoxy side chains provided a mechanochromic system that allows self-erasable imaging. Whereas PVs exhibit quenching of fluorescence in most cases during self-assembly, PE derivatives exhibit aggregation-induced emission. This property of PEs has been exploited for the development of stimuli-responsive security materials, especially for currency and documents. For instance, the blue fluorescence of a PE attached to hydrophilic oxyethylene side chains coated on a filter paper upon contact with water changes to cyan emission due to the change in the molecular packing. Interestingly, the mole...

Self-assembly is a viable approach to create soft functional materials with architectural diversity and property variations. Among the large number of different chromophores used, borondipyrromethene (Bodipy) dyes find a unique space because of their promising photophysical properties such as high molar absorptivity, fluorescent quantum yield and excellent photostability along with the associated synthetic ease. Recently, research on Bodipy dyes has experienced a surge of activities in view of favorable self-assembling properties. In this review, recent developments in self-assembled Bodipy dyes and their significance in various applications are discussed.

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Self-assembled synthetic hybrid materials are an important class of artificial materials with potential applications in various fields ranging from optoelectronics to medicine. The noncovalent interactions involved in the self-assembly process offer a facile way to create hybrid materials with unique and interesting properties. In this context, selfassembled hybrid materials based on carbon nanotubes (CNTs), graphene, and graphene derivatives such as graphene oxide (GO) and reduced graphene oxide (RGO) are of particular significance. These composites are solution processable, generally exhibit enhanced electrical, mechanical, and chemical properties, and find applications in the fields of light harvesting, energy storage, optoelectronics, sensors, etc. Herein, we present a brief summary of recent developments in the area of self-assembled functional hybrid materials comprising one-dimensional (1D) or twodimensional (2D) carbon allotropes and synthetic π-systems such as aromatic molecules, gelators, and polymers.

Optical properties of π‐systems are of great significance for a wide range of applications in materials and biology. Aggregation and self‐assembly induced emission are one of such phenomena. Herein, the self‐assembly induced modulation of the emission of p‐phenyleneethynylene (PE) chromophores bearing linear achiral (1) or branched chiral (2) alkoxy chains is reported. Self‐assembled structures of both 1 and 2 from n‐decane exhibit enhanced emission with fluorescence quantum yield (ΦF) values of 0.34 and 0.25, respectively, whereas these molecules are less‐emissive in chloroform (ΦF = 0.02). Transmission electron microscopy and fluorescence microscopy studies reveal the formation of entangled blue‐emissive fibers for 1 and supercoiled helical blue‐emissive fiber bundles for 2. At higher concentrations (8.8 × 10−3 m for 1 and 23.6 × 10−3 m for 2) in n‐decane, intense blue‐emitting gels are formed. Significant shift in the emission toward longer wavelength can be seen from solution state to aggregates to the gel state. The wide‐angle X‐ray scattering and fluorescence data indicate that the interdigitated lamellar assembly with weaker π‐stacking and the resultant restriction of rotation of the PE chromophores are responsible for the enhanced emission of the self‐assembled gel state.

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