Evidence for Effective p(Z)−π(Ar) Conjugations (Z = S, Se, and Te, as Well as Z = O) in 9-(Arylchalcogenyl)triptycenes: Experimental and Theoretical Investigations

The p(Z)−π(Ar) conjugations must operate fully in the ground states of 9-(arylchalcogenyl)triptycenes (p-YC6H4ZTpc:1 (Z = O), 2 (Z = S), 3 (Z = Se), and 4 (Z = Te)), where the p-YC6H4 group is placed in the bisected area between two phenyl planes of the triptycyl group with the parallel orientation. The ground-state geometries, which we call (A: pl), are confirmed by X-ray analysis. However, the conjugations never operate in the transition states between (A: pl) and/or the topomeric structures (A′: pl′), where the Z−CTpc bond is perpendicular to the plane. The site-exchange processes correlate to the conjugations. Temperature-dependent 1H NMR spectra are analyzed for 2 and 3 to demonstrate the effective p(Z)−π(Ar) conjugations. The activation energies for the interconversion between (A: pl) and (A′: pl′) (GR: gear process) were obtained for 2 (ΔG⧧GR(2)) and 3 (ΔG⧧GR(3)). ΔG⧧GR(3) correlate well with ΔG⧧GR(2), and ΔG⧧GR(2) are well analyzed by the Hammett-type dual parameters. ΔG⧧GR(2) and ΔG⧧GR(3) are demonstrated to be controlled by the resonance interaction of the p(Z)−π(C6H4)−p(Y) conjugations. QC calculations are performed on the ground and exited states of 1−4, which clarify the effective p(Z)−π(C6H4)−p(Y) conjugations for Z of heavier atoms.