Correlation between structural studies and third order NLO properties of selected new quinolinium semi-organic compounds

Abstract

New quinolinium semi-organic compounds of formula ( C 9 H 8 N ) 2 + · SO 4 2 - , H 2 O ( I) (bis-quinolinium sulphate monohydrate) and ( C 9 H 8 N ) + · NO 3 - ( II) (quinolinium nitrate) have been synthesized and characterized by UV–Vis absorption spectroscopy, nonlinear optical (NLO) measurements and by single crystal X-ray diffraction. The third order nonlinear optical properties of ( I) and ( II) were investigated using two methods: the degenerate four wave mixing technique (DFWM) performed in solution at λ = 532 nm and the third-harmonic generation (THG) measurements carried out on thin films at λ = 1064 nm. The NLO measurements showed that compound ( I) presents better nonlinear optical properties compared to compound ( II). To understand further the optical behaviour of ( I) and ( II), the crystal structures of both compounds were determined from accurate single crystal X-ray diffraction measurements performed at 100 K. The crystallographic studies revealed the key role of the intermolecular interactions and the molecular arrangements in the enhancement of the NLO properties.