Herein we describe the synthesis and characterization of fully-fused tetraphenyl-thieno[3,4-d]pyridazine 1 and N-methylpyrrolo[3,4-d]pyridazine 2 with two embedded seven-membered rings. Owing to the incorporated heptagon, both of 1 and 2 exhibited Cs-symmetric saddle conformations in the solid state with mean plane deviation around 0.38 Å. π-Expanded thienopyridazine 1 showed a 1-D columnar packing along the b axis with net dipole moment aligning perpendicular to the b axis in the polar crystal system Pc. On the other hand, 2 formed a partially π-stacked brick-work structure in the crystal. In addition to the Cs-symmetric saddle conformations found in the crystals, DFT calculation found C2-symmetric twisted conformations of both 1 and 2 close in energy to the saddle conformations. The barrier of conformational interconversion was calculated to be 32 (1) and 31 kJ·mol−1 (2), and the interconversion occur fast even at −60 °C as evidenced by VT-NMR studies. While 1 and 2 have moderately curved structures, optical and electrochemical studies revealed effective π-conjugation over the fused diphenylene units, which is also supported by DFT calculation. As the result of the intrinsic large dipole moment of thieno- and pyrrolo-pyridazines and the notably curved structure, 1 (2) has a substantial out-of-plane dipole moment of 2.0 (3.3) D in the saddle conformations.

Synthesis and characterization of doubly diphenylene-fused 2,3,6,7-tetraazanaphthalene 1 are described. Single-crystal X-ray diffraction analysis showed the highly twisted structure of 1 with a degree of twisting of 13.0°/Å, which is one of the largest values for a π-system. In the crystal, molecules of 1 formed an orthogonal one-dimensional column with π-stacking of diphenylene moieties and a short intermolecular C···N distance due to lone-pair/π* interaction, which is a rare example of lone-pair/π* interaction in a supramolecular assembly.

Herein, we describe the synthesis and characterization of fully fused tetraphenylthieno [3,4-d]pyridazine 1 and N-methylpyrrolo [3,4-d]pyridazine 2 with two embedded seven-membered rings. Owing to the incorporated heptagon, 1 and 2 exhibited C s -symmetric saddle conformations in the solid state with mean plane deviation around 0.38 Å. π-Expanded thienopyridazine 1 showed a one-dimensional (1-D) columnar packing along the b axis with net dipole moment aligning perpendicular to the b axis in the polar crystal system Pc. On the other hand, 2 formed a partially πstacked brick-work structure. In addition to the C s -symmetric saddle conformations found in the crystals, density functional theory (DFT) calculation found C 2 -symmetric twisted conformations of both 1 and 2 close in energy to the saddle conformations. The barrier of conformational interconversion was calculated to be 32 (1) and 31 kJ•mol −1 (2), and the interconversion occurs fast even at −60 °C as evidenced by variable-temperature (VT)-NMR studies. While 1 and 2 have moderately curved structures, optical and electrochemical studies revealed effective π-conjugation over the fused diphenylene units, which is also supported by DFT calculation. As the result of the intrinsic large dipole moment of thieno-and pyrrolopyridazines and the notably curved structure, 1 (2) has a substantial out-of-plane dipole moment of 2.0 (3.3) D in the saddle conformations.