Molecular and supramolecular structural and photophysical features regulated by the number of nitrile groups on the cyclic triimidazole scaffold

The crystalline mono-, di-, and tri-nitrile substituted derivatives of triimidazo[1,2-a:1′,2′-c:1″,2″-e][1,3,5]triazine, cyclic triimidazole (TT), were synthesized in a two-step synthetic protocol, where TT was first subjected to halogenation to obtain iodinated compounds TT-xI, which were then treated with cuprous cyanide to obtain the targeted nitrile derivatives, TT-xCN (x = 1–3). All compounds belong to the monoclinic crystal system and crystallize in the P21/c space group (P21/n crystal setting for TT-3CN) with Z = 4 (Z′ = 1). The crystal packing in TT-1CN and TT-2CN is governed by CH⋯N edge-to-edge short contacts that combine the molecules in H-bonded layers, while π-π co-facial stacking interactions between the molecules from adjacent layers provide a parallel arrangement of the H-bonded arrays. The reduced number of H-atoms and their shielding by bulky nitrile groups in TT-3CN result in dominating C(N)⋯N(C) face-to-face contacts and herring-bone crystal packing. The distribution of intermolecular interactions in the three nitrile derivatives was estimated using Hirshfeld surface analysis. Photophysical studies on the three compounds revealed that TT-2CN and TT-3CN display aggregation induced emissive features, while TT-1CN behaves as an aggregation quenched luminophore. In the solid state, all luminophores reveal blue fluorescence and room temperature phosphorescences of molecular and supramolecular origins. For all three compounds, two oxidation (Ia, IIa) and two reduction (Ic, IIc) peaks, corresponding to irreversible redox processes, were observed.