Three N-ethylcarbazole derivatives have been synthesized and tested for non-linear optical (NLO) properties. The compounds are 2-(9-ethyl-9H-carbazol-3-ylmethylene)malononitrile, C(18)H(13)N(3), (IIIa), 2-cyano-3-(9-ethyl-9H-carbazol-3-yl)thioacrylamide, C(18)H(15)N(3)S, (IIIb), and 3-(9-ethyl-9H-carbazol-3-yl)-2-(4-phenyl-1,3-thiazol-2-yl)acrylonitrile, C(26)H(19)N(3)S, (V). It was found that the molecules of (IIIa) and (V) are nearly planar, while non-planarity is more pronounced for (IIIb). Molecules of (IIIa) and (V) exhibit herring-bone packing motifs. In (IIIb), the molecules form layers coplanar with (-201), within which they form centrosymmetric dimers via N-H...S hydrogen bonds.