Tuning the optical properties of N-aryl benzothiadiazole via Cu(II)-catalyzed intramolecular C-H amination: the impact of the molecular structure on aggregation and solid state luminescence

Solid-state luminescent organic molecule materials recently have shown attractive application prospects in different areas, especially in optoelectronics. However, compared to molecules in dilute solution, the bulk properties in organic solids are more difficult to predict or modulate, as they are often strongly affected by the subtle interplay of the molecular orientation/arrangement in the condensed phase. Herein, three compounds (1-3) were designed to explore the impact of the molecular structure on the aggregation mode and the solid-state luminescence of benzothiadiazole derivatives. 1 was successfully converted to semi-fused 2 or hetero-[5]helicene 3 via the direct intramolecular C-H amination using only an inorganic Cu(II) salt catalyst. Interestingly, H-aggregation induced emission was observed at 640 nm in the crystal of 1, while orange J-aggregation emission and yellow H-aggregation emission were found in the crystals of 2 and 3, respectively. All three compounds showed reversible piezochromic behaviors with favorable sensitivities. Compared with flexible 1 or rigid 3, semi-rigid 2 was more easily affected by external pressure to trigger the remarkably piezochromic behavior (the emission wavelength was shifted from 610 nm to 739 nm). Moreover, 1 displayed remarkably red-shifted electroluminescence (EL) at 696 nm in a non-doped OLED device. The development in this area will provide a useful strategy to design and synthesize intriguing benzothiadiazole-based solid luminescent materials.