Slow evaporation method was employed to grow an organic crystal: guanidinium hydrogen succinate (GHS). Monoclinic structure of GHS was confirmed by single-crystal X-ray diffraction study and its space group was determined to be $P2_1/c$. Different functional groups present in GHS were estimated qualitatively by Fourier transform infrared analysis. The crystalline quality of the grown GHS was ascertained by high-resolution X-ray diffraction study. The UV–Vis absorption spectrum reveals a lower cut-off wavelength of 235 nm. The minimum absorption shows the wide optical transparency in the entire visible region.Work hardening co-efficient value ($n = 1.7$) shows that the GHS crystal belongs to soft material category. Behaviour of dipoles in the crystal was examined through dielectric study. The third-order nonlinear optical analysis wascarried out on GHS crystal through Z-scan technique. The nonlinear refractive index ($n_2$), nonlinear absorption coefficient ($\beta$) and third-order nonlinear optical susceptibility ($\chi^{(3)}$) were estimated to be $−5.78\times 10^{−8}$ cm$^2$ W$^{−1}$, $0.72\times 10^{−4}$ cm W$^{−1}$ and $8.09 \times 10^{−6}$ esu, respectively.

Guanidinium hydrogen glutarate (GHG) was synthesized by slow evaporation method. X-ray diffraction (XRD) study reveals that GHG crystallized into a triclinic system with the space group P$\bar{1}$. Crystallinity of the obtained GHG crystal was investigated with the help of the powder XRD analysis. High-intensity peak observed at 28° of the (1 –1 –2) plane confirms the good crystallinity of the GHG crystal. The crystalline nature of the synthesized crystal was tested through high-resolution XRD. The presence of different functional groups in the GHG material was analysed by the Fourier transform infrared and FT-Raman spectra. UV–Vis spectral analysis of the GHG material demonstrates 98% transmittance with a cut-off wavelength at 230 nm. The bandgap value of GHG is 5.01 eV. A peak at 421 nm is observed in the emission spectrum. The results imply that GHG crystals have a blue fluorescence emission. The thermal stability of the grown crystal was determined using thermal analysis. The GHG compound is stable up to 244°C and it has good degree of crystallinity. The mechanical behaviour of the title crystal was measured using microhardness studies. The GHG crystal shows that it belongs to soft material category. A dielectric study of the crystal was analysed at diverse temperatures. Third-order nonlinear optical (NLO) susceptibility is determined using through Z-scan studies. The nonlinear refractive index ($n_2$), nonlinear absorption coefficient (${\beta}$) and third-order NLO susceptibility (${\chi}^(3)$) were estimated to be –1.8545 ${\times}$ 10$^{–8}$ (cm$^2$ W$^{–1}$), 3.8015 ${\times}$ 10$^{–4}$ (cm W$^{–1}$) and 2.2150 ${\times}$ 10$^{–5}$ (esu), respectively. Optical limiting property of the GHG compound has also been discussed.