There　is　presently　a　great　demand　for　nonlinear　optical　(NLO)　crystals　that　can　demonstrate　both　strong　second-harmonic　generation　(SHG)　and　high　birefringence　in　emerging　spin-orbit　angular　momentum　photonic　technologies.　Here　we　report　a　new　chiral　trithiocyanate　compound,　K4(HC3N3S3)2·H2O,　which　is　composed　of　highly　π-conjugated　[HC3N3S3]2−　rings　and　is　structurally　analogous　to　commercial　NLO　crystal　β-BaB2O4　(BBO).　Compared　with　BBO,　which　has　optimally　arranged　π-conjugated　[B3O6]3−　rings,　K4(HC3N3S3)2·H2O　does　not　have　an　optimal　arrangement　of　[HC3N3S3]2−　rings.　However,　this　trithiocyanate　exhibits　a　significantly　enhanced　SHG　response　of　up　to　1.8　times　that　of　BBO　and　an　enhanced　birefringence　of　up　to　0.402　at　the　wavelength　of　550　nm　(about　3.3　times　that　of　BBO).　The　first-principles　calculations　show　that　the　π-conjugated　[HC3N3S3]2−　is　the　cause　of　the　superior　optical　properties　of　K4(HC3N3S3)2·H2O.　These　findings　demonstrate　that　the　π-conjugated　[HC3N3S3]2−　is　an　excellent　bi-functional　“material　gene”　and　merits　more　attention　in　the　study　of　optical　integrated　devices　for　emerging　photonic　technologies.[Figure　not　available:　see　fulltext.]　©　2023,　Science　China　Press.