A series of fused three-ring compounds have been synthesized and characterized for their possible use as organic crystals for second-harmonic generation. Polymer films doped with these compounds were aligned via corona poling and their second order non-linear optical properties compared with layers doped with stilbene like molecules. Values of ¼β0 have been obtained and the effects of different heteroatoms and substituents on λ max and on ¼β0 were examined. An X-ray diffraction crystal structure on one member of the series, 1,2,4-Trichloro-8-nitro-phenoxazin-3-one (Compound 1), revealed a centrosymmetric crystal habit in a P21/n space group, with a = 9.829(3), b = 8.300(2) and c = 15.542(4) Å. Final R(F) = 0.0939 for 754 reflections where I σ; 3σ(I).