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The title compound, C21H15N3O3, crystallizes in two polymorphic forms. In the orthorhombic polymorph, (I), in space group Fdd2 with Z' = 1, the molecules lie in general positions, while in the monoclinic polymorph, (II), in space group C2/c with Z' = 1/2, the molecules lie across twofold rotation axes. In each polymorph, the molecules are linked by a single C-H.pi(arene) hydrogen bond, forming chains in polymorph (I) and sheets in (II).

Di-mu-chloro-bis[chloro(triphenylphosphine)mercury(II)], [Hg2Cl4(C18H15P)2], (I), and di-mu-bromo-bis[bromo(triphenylphosphine)mercury(II)], [Hg2Br4(C18H15P)2], (II), have been reinvestigated at 120 K. The molecules of (I) lie across inversion centres in space group P2(1)/n, and in both (I) and (II) the complexes are linked into three-dimensional frameworks by a combination of C-H...X (X = Cl and Br) and C-H...pi(arene) hydrogen bonds. At 120 K, di-mu-iodo-bis[iodo(triphenylphosphine)mercury(II)], [Hg2I4(C18H15P)2], (III), crystallizes as a new polymorphic form having Z' = 1/2, where the complexes lie across inversion centres in space group P2(1)/n; the complexes are linked into sheets by a combination of C-H...I and C-H...pi(arene) hydrogen bonds. In the Z' = 1 polymorph of this compound, a single C-H...I hydrogen bond generates simple chains.

Triphenylphosphoniumfluorenylide (TPPFY), a fluorescent fluorene attached molecule, showed polymorphism, benzene solvent induced aggregation enhanced emission (AEE) and external stimuli responsive on–off fluorescence switching.