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.

p(Z)−π(Ar)共轭需在9-芳基硫族取代基三蝶烯（9-(arylchalcogenyl)triptycenes，记为p-YC₆H₄ZTpc：1(Z=O)、2(Z=S)、3(Z=Se)、4(Z=Te)）的基态下完全发挥作用，其中p-YC₆H₄基团以平行取向位于三蝶基的两个苯环平面之间的平分区域内。我们将该基态几何构型记为(A: pl)，其结构已通过X射线衍射分析得到验证。然而，该共轭效应在(A: pl)与/或拓扑异构结构(A′: pl′)之间的过渡态中完全不起作用，此时Z−CTpc键与该平面垂直。位点交换过程与该共轭效应密切相关。通过对化合物2和3的变温核磁共振氢谱进行分析，证实了p(Z)-π(Ar)共轭的有效性。我们得到了(A: pl)与(A′: pl′)之间互变（即齿轮过程GR）的活化吉布斯自由能，分别对应化合物2的ΔG⧧GR(2)和化合物3的ΔG⧧GR(3)。ΔG⧧GR(3)与ΔG⧧GR(2)具有良好的相关性，且ΔG⧧GR(2)可通过哈米特双参数进行良好的拟合分析。实验证实，ΔG⧧GR(2)与ΔG⧧GR(3)均受p(Z)-π(C₆H₄)-p(Y)共轭的共振相互作用调控。我们对化合物1~4的基态与激发态进行了量子化学（QC, Quantum Chemistry）计算，结果阐明了对于重原子Z而言，p(Z)-π(C₆H₄)-p(Y)共轭具有有效性。