With an aim to understand the photophysical behavior of twisted organic fluorescent molecules in their aggregated state, two twisted biaryl molecules, namely, 9,9′-bianthryl and 10,10′-dicyano-9,9′-bianthryl, have been synthesized and characterized by conventional spectroscopic methods. To understand the role of C–C bond twisting on the photophysical response of biaryl aggregates, monoaryl counterparts (anthracene and 9-anthracenecarbonitrile) of the biaryl systems are also investigated. Photophysical behaviors of these systems along with their monoaryl counterpart are investigated in both solution and aggregated state. Investigations reveal that fluorescence spectra of the biaryl compounds show blue-shifted emission upon aggregation. Interestingly, no blue shift of the emission has been observed for monoaryl aggregates. Photophysical data of biaryl systems compared to monoaryl unit reveal that change in geometry, during self-assembly process, disfavors the formation of charge-transfer state, which eventually causes blue shift in the emission upon aggregation. In addition to this, potential of these systems toward signaling of nitroaromatic explosive has also been explored. Among all of the nitroaromatics, the highest fluorescence quenching is observed for nitrophenols (say picric acid (PA)). The investigation also reveals that compared to monoaryl systems, biaryl systems are more responsive to fluorescence quenching by nitroaromatics. Perrin’s model of quenching sphere action has been attributed to nitrophenol (PA) selective signaling behavior of biaryl systems.

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With an aim to understand the interaction between the inorganic and organic components in inorganic–organic hybrid nanostructured materials, we have designed and developed an inorganic–organic nanohybrid associate comprising inorganic fluorescent Au nanoclusters (NCs) and organic J-aggregates of a cyanine-based dye (S2165). The present system is quite interesting as in contrast to previously constructed nanohybrid systems where fluorescent quantum dots are integrated with an organic dye, the present system is developed using fluorescent gold nanoparticles and organic J-aggregates. The hybrid system has been characterized by spectroscopic and microscopic techniques. Steady-state absorption and emission and time-resolved fluorescence measurements have been performed to understand the optical properties of this hybrid system. In particular, the interparticle electronic interaction has been investigated by monitoring nonradiative energy transfer from fluorescent Au NCs (donor) to organic J-aggregates (acceptor). The fluorescence resonance energy transfer (FRET) event for the current system has been verified by various methods. ζ-Potential measurements and thermodynamic calculations have suggested that the interaction between Au NCs and J-aggregates in the hybrid associate is electrostatically driven. The analysis of data based on Förster theory has revealed that the energy transfer efficiency from inorganic to organic particles is very high. The observation of the high energy transfer efficiency in the present inorganic–organic hybrid associate is quite interesting as these results suggest that a metal-based system can also be very useful in designing a highly efficient light-harvesting system for various optoelectronic applications. Interestingly, both Au NCs and the Au–J-aggregate hybrid system are found to be cell-permeable and suitable for bioimaging studies. Additionally, because of the nontoxic nature of these systems, they can also be used in many biological applications.

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