Influence of organic dopants on the optical properties of 4-N,N′-dimethylamino-N′-methyl stilbazolium tosylate crystals

•An increased growth rate along the c-axis in the 2A5NPTS doped crystal.•The umbrella mode of the methyl group contributing to electro-optic effect of the crystal.•The band at 705 nm for benzene ring to be an effective push–pull NLO system•Enhanced Twisted Intramolecular Charge Transfer by NO2 group in the doped samples.

Organic crystals of 4-N,N′-dimethylamino-N′-methyl stilbazolium tosylate (DAST), 2-amino-5-nitro pyridinium (2A5NP) and 2-amino-5-nitro pyridine toluene sulfonate (2A5NPTS) doped DAST crystals were grown by slow cooling method. The powder samples were examined by X-ray diffraction to estimate the lattice parameter values of the crystals. Fourier Transform Infra-Red (FT-IR) and Fourier Transform-Raman (FT-Raman) spectroscopic studies were performed to identify the various functional groups associated with the crystals. The four strong vibrational modes were observed at 1161 cm−1, 1181 cm−1, 1346 cm−1 and 1577 cm−1 contributing to linear electro-optic effect in DAST crystals. The Density Functional Theory (DFT) was used for FT-IR and FT-Raman analysis by means of the hybrid functional DFT/B3LYP with 6-311 G (d, p) basis set. The optical band-gaps were calculated from the UV–vis and photoluminescence spectra of pure and doped DAST samples.