<title>Synthesis and SHG effect of some cyclotriphosphazene derivatives</title>

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ABSTRACT Twenty derivatives of hexachiorocyclotriphosphazene were synthesised by substituted reaction. The structure of thecyclotriphosphazenes were identified by i.r. uv-vis, n.m.r. and elemental analysis, proving that they are fully substitutedcyclotriphosphazenes. Kurtz powder determination of SHG showed that two of them displayed SHG effect. X-raydiffraction determination of N3P3(OC6H4F)6 is presented to explain SHG effect.Keyword cyclotriphosphazene, synthesis, SHG effect 1.INTRODUCTION It is almost a routine procedure in designing organic second order nonlinear optical (NLO) molecules to introduceelectronic push and pull groups to the head and end of a conjugated system. However, there is a sophisticated example,i.e.2,4,6-trinitro-3,5-diamino-aniline (TBTA) , which attached three push and three pull electronic groups at six end ofbenzene ring alternatively. There is no dipole moment at ground state, no centrosymmetry in the molecule. Non-centralalignment ofthe TBTA molecules resulted in NLO effect ofthe crystal (1).It is well known that cyclotriphosphazene ring normally has a planar molecular structure with a d-p conjugated system,somehow similar to the benzene ring. It possesses a non-centrosymmetric structure. Furthermore, it is easy to attachpolar groups to the ring through substitution reaction of hexacyclotriphosphazene (N3P3C13) with a variety of organiccompounds bearing hydroxy or amino groups. It is expected that this non-centrally conjugated structure may make itsderivatives manifest second harmonic generation (SHG) effect. In this work, twenty derivatives of cyclotriphosphazenesubstituted by phenols, thiophenols or anilines have been synthesised and characterised. SHG effect was determined.Single crystal structure ofthe compound N3P3(-O-C6H4F)6 was determined by X-ray diffraction technique.