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.