Evaluation of structural, spectral, thermal and optical properties of an efficient centrosymmetric organic single crystal 2-[2-(4-diethylamino-phenyl)-vinyl]-1-methyl pyridinium tetrafluoroborate for nonlinear optical applications

A novel stilbazolium derivative crystals of 4-[2-(4-dimethyl amino-phenyl)-vinyl]-1-methyl-pyridinium+ bromide- (DMSB) single crystal: exploration of the growth, molecular structure, linear optical, and third order nonlinear properties

A novel third-order stilbazolium derivative single crystal, 4-[2-(4-dimethyl amino-phenyl)-vinyl]-1-methyl-pyridinium bromide (DMSB), was fruitfully harvested using methanol as a medium, through a slow evaporation technique. The solubility of the prepared DMSB powder was experimentally tested at different temperatures (30 °C to 50 °C) with a methanol solvent. Single crystal X-ray diffraction analysis (SCXRD) implied that the DMSB crystal crystallized in a centrosymmetric fashion (space group P21/c) with the monoclinic crystal system. The molecular weight of the element present in DMSB was confirmed by CHN elemental analysis. Nuclear magnetic resonance (NMR) spectroscopic study confirmed the molecular structure of the DMSB crystal. All the functional group vibrations raised from the title compound were studied using Fourier transform infrared spectroscopy (FTIR). From the UV-visible spectrum, the absorbance nature and band gap of the grown DMSB crystal were determined. The photoluminescence study of the grown crystal exhibited an emission peak at 660 nm, which is attributed to the red light emission in the EM spectrum. The morphological characteristics of the crystal were characterized using atomic force microscopy (AFM). Hirshfeld surface analysis was employed to quantitatively explore the non-covalent interactions that are accountable for the crystal packing. The third-order nonlinear susceptibility was determined experimentally and it was found to be 1.6 × 10-8 esu. These favourable Z-scan analysis results indicate that the DMSB crystal is a good candidate for different applications, such as photonics devices, optical computing, optical switches, and optical limiting.

Intramolecular charge transfer dynamics in the excited states of diphenylamine substituted 1,3,4-oxadiazole derivatives

The excited state dynamics processes of two diphenylamine substituted symmetric 1,3,4-oxadiazole derivatives in different solvents were studied through femtosecond transient absorption spectroscopy. It was revealed that in cyclohexane, the locally excited (LE) state relaxes to the intramolecular charge transfer (ICT) state within 2 ps timescale, then decays to the ground state. In tetrahydrofuran and acetonitrile, the ICT state can be stabilized via solvation, so besides the LE → ICT conversion within 1 ps, another ICT → solvent stabilized ICT (SSICT) conversion in the 1-200 ps time scale could also be observed, and eventually decay to the ground state. Whereas, ICT → SSICT process in acetonitrile is slower than that in tetrahydrofuran, which leads to radiationless deactivation dominates the ICT state deactivation process and low fluorescence quantum efficiency. These results offer a guidance to understand the relationship of low fluorescence quantum efficiency and excited state deactivation mechanism of organic π-conjugated molecules, which would be very helpful for designing new advanced opto-electronic materials.