Pressure-Dependent Luminescence and Absorption in 3,3′-Diamino-4,4′-azoxyfurazan: Secondary Bonding Interaction in Molecular Crystals

Abstract

3,3′-Diamino-4,4′-azoxyfurazan (DAAF) is a new energetic material and has potential for application in many fields. Few works about its luminescence under high pressure have been reported so far. To probe its behavior of emission and electronic structure evolution, fluorescence, absorption, Raman, and Fourier transform infrared spectroscopies were performed under high pressure. Time-dependent density functional theory was carried out to reveal the luminescence mechanism of DAAF under ambient conditions. The yellow-green emission of DAAF mainly originated from the π* → π transition. The absorption edge shifted to red, and the color changed from yellow to dark with the increasing pressure. Two electronic structure changes were observed at ∼3 and ∼12 GPa because of the variation of hydrogen bond network and distortion of the molecular structure. The strengthened secondary bonding interactions and a slightly enlarged π-conjugation system resulted in the evident enhancement in the fluorescence intensity and moderate red shift below 3.5 GPa. The fluorescence spectra presented red shift and gradually lost intensity because of the activated π···π intermolecular interaction between layers and the canting and dislocating of p z orbitals above 3.5 GPa. Besides that, slipping, compression, and rearrangement of DAAF further strengthened the π···π interaction and decreased the gap between the lowest occupied molecular orbital and highest occupied molecular orbital at about 10 GPa. The current results reveal that there exists no structure transformation, only conformation change with electronic structure changes under high pressure up to 23 GPa.

Growth regulation of an easily crystallized organic long-persistent luminescence system with in situ anti-counterfeiting applications

“…42,43 Concurrently, the potential interactions between the host and guest molecules contribute to a slight redshift in the fluorescence emission spectrum of the doped material relative to that of the guest molecules alone. [44][45][46] Such observations further reinforce the notion that the photophysical processes in doped crystals primarily originate from the internal guest molecule p-TPD. As shown in Fig.…”

Pressure-Induced In Situ Construction of P-CO/HNIW Explosive Composites with Excellent Laser Initiation and Detonation Performance

“…The geometric optimization of the structures and frequency analyses were carried out using the B3LYP functional with the 6-31+G* basis set. The optimized P-CO structure was introduced into the energy module, and its excited electronic states were investigated in accordance with the time-dependent theory at the level of B3LYP/6-311. − …”