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Fluorescence spectrum of pyrene molecule in solution form has been of interest in the research community for more than six decades. Sensitivity of these molecules to solvent polarity makes them active probes for sensing impurities. Pyrene molecules when excited form an excimer complex with another molecule in the ground state, typically by the pi - pi orbital interaction. Fluorescence of these excimers are red shifted and results in structureless broad emission band. Pyrene is well-suited for studies on biophysical phenomena like lateral diffusion, inter or trans-bilayer movement of lipid and lateral organization of membranes. Microcrystals of aromatic compounds, such as perylene, coronene, anthracene and pyrene suspended in aqueous solutions, have been found to exhibit anomalous fluorescence spectra different from those of bulk. Our group has previously reported that the fluorescence spectra of single microcrystals are distinctly different from those of excimer emission but are similar to those of the crystalline thin film. In this work, we have used surfactant assisted self-assembly method to recrystallize nano-micro crystals of pyrene. We have undertaken this study in view of the recent investigation that reports excimer formation in nanocrystals. It has been found that while within the absorption band corresponding to the monomer, the excimer emission is dominant, higher aggregates continue to contribute due to excitation into the absorption tail of the nano-micro crystalline pyrene. By doping the synthesized microcrystals on polymer microcavities, whispering gallery modes (WGMs) were observed. WGMs find potential applications in sensing of several physical quantities like size, refractive index, pressure, temperature.
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