Arylazo-3,5-diphenylpyrazole Derivatives: Molecular Probes Exhibiting Reversible Light-induced Phase Transitions for Energy Storage and Direct Photolithographic Patterning.

We report azopyrazole photoswitches decorated with variable N-alkyl and alkoxy chains (for hydrophobic interactions) and phenyl substituents on the pyrazoles (enabling π-π stacking), showing efficient bidirectional photoswitching and reversible light-induced phase transition (LIPT). Extensive spectroscopic, microscopic, and diffraction studies and computations confirmed the manifestation of molecular-level interactions and photoisomerization into macroscopic changes leading to the LIPT phenomena. Using differential scanning calorimetric (DSC) studies, the energetics associated with those accompanying processes were estimated. The long half-lives of Z isomers, high energy contents for isomerization and phase transitions, and the stability of phases over an extended temperature range (-60 to 80 oC) make them excellent candidates for energy storage and release applications. Remarkably, the difference in the solubility of the distinct phases in one of the derivatives allowed us to utilize it as a photoresist in photolithography applications on diverse substrates.

A one-pot telescopic synthesis of benzo[b]carbazoles and exploration of their liquid crystalline properties.

We describe a diversity-oriented one-pot telescopic synthesis of various benzo[b]carbazoles with the naphthannulation of indoles as the key step, enabled by an intramolecular furan-olefin Diels-Alder reaction. This strategy is general and efficient across a wide range of substrates. We applied this method to synthesize and characterize the first benzo[b]carbazole-based liquid crystalline materials, where the unique molecular design led to the formation of a rare nematic phase at room temperature.

High Electrical Conductivity and Hole Transport in an Insightfully Engineered Columnar Liquid Crystal for Solution-Processable Nanoelectronics.

Discotic liquid crystals (DLCs) are widely acknowledged as a class of organic semiconductors that can harmonize charge carrier mobility and device processability through supramolecular self-assembly. In spite of circumventing such a major challenge in fabricating low-cost charge transport layers, DLC-based hole transport layers (HTLs) have remained elusive in modern organo-electronics. In this work, a minimalistic design strategy is envisioned to effectuate a cyanovinylene-integrated pyrene-based discotic liquid crystal (PY-DLC) with a room-temperature columnar hexagonal mesophase and narrow bandgap for efficient semiconducting behavior. Adequately combined photophysical, electrochemical, and theoretical studies investigate the structure-property relations, logically correlating them with efficient hole transport. With a low reorganization energy of 0.2 eV, PY-DLC exhibits superior charge extraction ability from the contact electrodes at low values of applied voltage, achieving an electrical conductivity of 3.22 × 10-4 S m-1, the highest reported value for any pristine DLC film in a vertical charge transport device. The columnar self-assembly, in conjunction with solution-processable self-healed films, results in commendably elevated values of hole mobility (≈10-3 cm2 V-1s-1). This study provides an unprecedented constructive outlook toward the development of DLC semiconductors as practical HTLs in organic electronics.

Self-assembled discotics as molecular semiconductors.

With the advent of a new era of smart-technology, the demand for more economic optoelectronic materials that do not compromise with efficiency is gradually on the rise. Organic semiconductors provide greener alternatives to the conventional inorganic ones, but encounter the challenge of balancing charge carrier mobility with processability in devices. Discotic liquid crystals (DLCs), a class of self-assembling soft organic materials, possess the perfect degree of order and dynamics to address this challenge. Providing unidimensional charge carrier pathways through their nanoscale columnar architecture, DLCs can behave as efficient charge transport systems across a wide range of optoelectronic devices. Moreover, DLCs are solution-processable, thus reducing the fabrication cost. In this article, we have discussed the approaches towards developing DLCs as semiconductors, focusing on their molecular design concepts, supramolecular structures and electronic properties in the context of their charge carrier mobilities.

Light Modulated Reversible "On-Off" Transformation of Arylazoheteroarene Based Discotics in Nematic Organization.

Three benzene-1,3,5-tricarboxamide (BTA) core-based molecular systems appended with phenylazo-3,5-dimethylisoxazole photoswitches at the peripheral position through variable-length alkoxy chains have been designed and synthesized. The supramolecular interactions of the mesogens provided discotic nematic liquid crystalline assembly as confirmed by polarized optical microscopy (POM) and X-ray diffraction (XRD) studies. Spectroscopic studies confirmed the reversible photoswitching and excellent thermal stability of the photoswitched states in solution phase and thin film. Also, atomic force microscopic (AFM) and POM investigations demonstrated the morphological changes in the self-assembly induced by the photoirradiation as monitored by the changes in the height profiles and optical appearance of the textures, respectively. Remarkably, the liquid crystalline discotic molecules showed reversible "on and off states" controlled by light at ambient temperature.

Discs to a 'Bright' Future: Exploring Discotic Liquid Crystals in Organic Light Emitting Diodes in the Era of New-Age Smart Materials.

With the advent of a new decade and the paradigm shift of every sphere of urban life to virtual platforms, it has become imperative for the global researcher community to channelize efforts into upgradation of the existing display-technology. In this context, discotic liquid crystals (DLCs) are a class of self-assembling organic materials that are recently being explored in fabricating the emissive layers of organic light emitting diodes (OLEDs). With their unique inherent structural and functional properties, they have the potential to challenge the currently prevailing OLED-emitters. Yet the applications of this promising class of materials in OLEDs have not been comprehensively reviewed in literature till now. In this account, we present an overview of the developments in the field of luminescent DLC-based emitters, supported by their associated photophysical phenomena and their performance parameters as emitters in fabricated OLED devices.