Synthesis of pi-Extended [1.1]Paracyclophanes, [1.1][n]PCP (n = 2, 3, and 4), and Their Through-space Conjugation

[1.1][n]Paracyclophanes ([1.1][n]PCPs) (3) with n = 2, 3, and 4, which consist of two [n]paraphenylene units connected by methylene bridges, were synthesized using short synthetic pathways with good overall yields. Single-crystal X-ray diffraction analyses reveal that the paraphenylene unit in 3 is bent, resulting in an elliptic core structure of 3. The facing bridgehead carbons of the paraphenylene units are separated by a distance much shorter than the sum of the van der Waals radii of sp2-carbon atoms. UV-vis absorption spectra, fluorescence spectra, electrochemical measurements, and theoretical calculations were used to demonstrate the presence of through-space (TS) conjugation in 3. Furthermore, host-guest complex formation between 3D (n = 3) and tetracyanoquinodimethane in the solid state was revealed.