This　work　reports　the　syntheses,　structures,　and　luminescence　properties　of　two　supramolecular　polymorphic　compounds　composed　of　a　hybrid　bismuth(III)　chloride　anion　and　an　imidazolium　cation,　namely　α-　(1)　and　β-　(2)　[Bmim][BiCl4(2,2′-bpy)]　(Bmim=1-butyl-3-methyl　imidazolium;　2,2′-bpy=2,2′-bipyridine).　They　are　the　first　two　examples　of　Bi3+-containing　ionic　liquids　(ILs).　Their　different　packing　modes　may　be　ascribed　to　the　rotational　flexibility　of　the　butyl　group　on　the　[Bmim]+　cation.　A　comparative　study　of　the　weak　intermolecular　interactions　present　in　the　two　polymorphs　has　been　performed　by　Hirshfeld　surface　and　two-dimensional　fingerprint　analyses.　Investigations　of　the　luminescence　properties　revealed　that　crystallization　induced　greenish-yellow　phosphorescence　with　quantum　yields　of　26.07　%　for　1　and　36.59　%　for　2,　which　are　among　the　highest　hitherto　reported　for　hybrid　halobismuthate　compounds.　The　difference　in　phosphorescence　may　be　attributed　to　the　different　weak　interactions　in　1　and　2,　especially　π–π　contacts.　This　work　opens　the　way　to　further　research　on　new　types　of　polymorphism-dependent　luminescent　materials　based　on　a　combination　of　rotationally　isomeric　IL　cations　with　organic　decorated　bismuth(III)　chloride　anions.　©　2017　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim