Structural and spectroscopical study of a 2,5-diphenyl-1,3,4-oxadiazole polymorph under compression

Abstract

The x-ray pattern and the Raman and luminescence spectra of crystalline 2,5-diphenyl-1,3,4-oxadiazole in one of its polymorphic forms (DPO II) have been investigated under pressure up to 5 GPa. The behaviour of the lattice parameters under compression was determined and it was found that the Murnaghan equation of state provides a good description of the volume–pressure relationship of DPO II. The values for the bulk modulus and its pressure derivative are K0 = 8.6 GPa and K′0 = 7.2. The analysis of the Raman spectrum under compression clearly shows the pressure-induced shift of the Raman modes to higher frequencies. The mode Grüneisen parameters for the lattice modes were determined. Additionally, it was found that the emission spectrum of DPO II moves to lower energies and that the luminescence intensity decreases when pressure is applied.

Pressure-Induced Reversible Amorphization in Hydrogen-Bonded Crystalline Phenyl Carbamate Form-I

“…Similarly, Raman bands in the internal mode region also gradually shift toward high frequencies, except for the sudden red-shifts of γ­(OCO) and γ­(CH). The increases in frequency may be explained by the shortened interatomic distances and increased effective force constants under crystal compression . Notably, the pressure-induced frequency shifts of the CO stretching mode involved in molecular associations via hydrogen bonds exhibit a blue shift throughout the whole pressure region.…”

“…The increases in frequency may be explained by the shortened interatomic distances and increased effective force constants under crystal compression. 48 Notably, the pressure-induced frequency shifts of the CO stretching mode involved in molecular associations via hydrogen bonds exhibit a blue shift throughout the whole pressure region. This blue shift indicates that the N− H•••O hydrogen bonds in PC form-I are strong and continuously strengthen with increasing pressure.…”

Nonvolatile Electrical Switching and Write-Once Read-Many-Times Memory Effects in Functional Polyimides Containing Triphenylamine and 1,3,4-Oxadiazole Moieties

“…As shown in Figure 1b, the OXTA monomer exhibits an intense emission peak at 436 nm, which is red-shifted by about 100 nm in comparison to the emission of 2,5-diphenyl-1,3,4-oxadiazole. 33 This large red shift arises probably from the intense CT between the triphenylamine and oxadiazole groups in OXTA. The fluorescent quantum yield (Φ F ) of the monomer (OXTA) in chloroform was estimated by comparison with the PL of standard 9,10-diphenylanthracene.…”

Pressure-induced phase transition of 4-aminobenzonitrile: the formation and enhancement of N–H⋯N weak hydrogen bonds

“…5b-e. From 1 atm to 0.2 GPa, most internal modes moved to the high frequency regions, indicating that the vibrations of most chemical groups on 4-aminobenzonitrile molecules were enhanced under high pressure. 49,50 The blue shis of C-H and N-H stretching modes indicate the initial N-H/N interactions are even weaker than normal weak hydrogen bonds, which usually show red shis under compression. 36 When the pressure reached 0.2 GPa, the ph-N in-plane bending, ring CC inplane def., ring CH out-plane bending, ring breathing, ring CH in-plane bending, n s (ph-CN), C^N stretching, NH 2 scissoring, ring C]C stretching, C-H stretching and N-H stretching modes showed slightly discontinuous shis.…”