Deepak Asthana

Abstract: The generation of the first persistent radical cation of naphthalenediimide with Cu2+/Fe3+ under ambient conditions is reported. An alternate anionic trigger generates a persistent radical anion within the same motif. Steric protection and H-bonding enhances the half-life of radical cation by 290-fold. The radical anion and cation have orthogonal spin density, panchromatic and NIR optical bands, which can be applied as attractive multichannel probes.

Abstract: We report unique and spontaneous formation of hydrogels of perylene derivatives with melamine. The luminescent gel network is formed by H-type aggregation of the perylene core, supramolecularly cross-linked by melamine units. As a result of controlled aggregation in the extended nanofibers, strong exciton fluorescence emission is observed.

Abstract: Herein we report the first applications of TCNQ as a rapid and highly sensitive off-the-shelf cyanide detector. As a proof-of-concept, we have applied a kinetically selective single-electron transfer (SET) from cyanide to deep-lying LUMO orbitals of TCNQ to generate a persistently stable radical anion (TCNQ•–), under ambient condition. In contrast to the known cyanide sensors that operate with limited signal outputs, TCNQ•– offers a unique multiple signaling platform. The signal readability is facilitated through multichannel absorption in the UV–vis–NIR region and scattering-based spectroscopic methods like Raman spectroscopy and hyper Rayleigh scattering techniques. Particularly notable is the application of the intense 840 nm NIR absorption band to detect cyanide. This can be useful for avoiding background interference in the UV–vis region predominant in biological samples. We also demonstrate the fabrication of a practical electronic device with TCNQ as a detector. The device generates multiorder enha...

Abstract: Urea-based molecular constructs are shown for the first time to be nonlinear optically (NLO) active in solution. We demonstrate self-assembly triggered large amplification and specific anion recognition driven attenuation of the NLO activity. This orthogonal modulation along with an excellent nonlinearity-transparency trade-off makes them attractive NLO probes for studies related to weak self-assembly and anion transportation by second harmonic microscopy.

Abstract: Aggregation-induced photon upconversion (iPUC) based on a triplet–triplet annihilation (TTA) process is successfully developed via controlled self-assembly of donor–acceptor pairs in organogel nanoassemblies. Although segregation of donor from acceptor assemblies has been an outstanding problem in TTA-based UC and iPUC, we resolved this issue by modifying both the triplet donor and aggregation induced emission (AIE)-type acceptor with glutamate-based self-assembling moieties. These donors and acceptors co-assemble to form organogels without segregation. Interestingly, these donor–acceptor binary gels show upconversion at room temperature but the upconversion phenomena were lost upon dissolution of the gels on heating. The observed changes in TTA-UC emission were thermally reversible, reflecting the controlled assembly/disassembly of the binary molecular systems. The observed on/off ratio of UC emission was much higher than that of the aggregation-induced fluorescence of the acceptor, which highlights the important role of iPUC, i.e., multi-exciton TTA for photoluminescence switching. This work bridges iPUC and supramolecular chemistry and provides a new strategy for designing stimuli-responsive upconversion systems.

Abstract: In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...

Abstract: This comprehensive review surveys developments over the past decade in the field of naphthalene diimides (NDIs). It explores their application toward: supramolecular chemistry; sensors; host–guest complexes for molecular switching devices, such as catenanes and rotaxanes; ion-channels by ligand gating; gelators for sensing aromatic systems; catalysis through anion−π interactions; and NDI intercalations with DNA for medicinal applications. We have also explored new designs, synthesis, and progress in the field of core-substituted naphthalene diimides (cNDIs), and their implications in areas such as artificial photosynthesis and solar cell technology. Also presented are some interesting synthetic routes and procedures that can be used toward further development of NDI-bearing compounds for future applications. Finally, we conclude with our views on NDI chemistry for future research endeavors, and we outline what we believe are the key obstacles that need to be overcome for NDIs to see real world applications.

Abstract: The presence of cyanide ions in surface water is not only caused by industrial waste but also by biological processes. Owing to the extreme toxicity of cyanide in physiological systems and its widespread presence in the environment, considerable attention has been given to the development of methods for the detection of cyanide. Among the most simple, inexpensive and rapid methods to detect cyanide ions are chemosensors that rely on fluorometric and colorimetric responses. This review, which focuses on CN− fluorescence and colorimetric chemosensors that have been developed since 2010, follows a format in which the sensors are classified according to their structural features and reaction mechanisms. Finally, a general overview of the design of fluorometric and colorimetric chemosensors for CN− is provided.