Helical Oligophenylene Linked with [2.2]Paracyclophane: Stereogenic π‐Conjugated Dye for Highly Emissive Chiroptical Properties
Masashi Hasegawa, Yuki Ishida, Hiroaki Sasaki, Sumire Ishioka, Kazuteru Usui, Nobuyuki Hara, Maho Kitahara, Yoshitane Imai, Yasuhiro Mazaki
Abstract
Abstract A stereogenic π‐system based on dimer ( 2 ) and trimer ( 3 ) of [2.2]paracyclophane (PC) and biphenyl was prepared and its structural, photophysical, and chiroptical properties were investigated. X‐ray analysis revealed that the quaterphenyl moieties in 2 adopt a double helical structure anchoring [2.2]PC from both sides. Furthermore, 3 forms a isosceles triangle structure with a large chiral cavity. A homodesmotic reaction using DFT calculations revealed that 2 has a larger strain energy than 3 owing to its highly twisted phenylene linkers. Electronic and circular dichroic (CD) spectra were recorded in CH 2 Cl 2 solution. The spectra of both 2 and 3 are similar, and their longest absorption band accompanying a remarkable Cotton effect is attributed to the transition from HOMO to LUMO, which is delocalized to the quaterphenyl moiety. These compounds exhibit fairly high fluorescence quantum yields ( ϕ =0.70–0.83) and moderate dissymmetry factor (| g CPL |=1.6×10 −3 ) in circularly polarized luminescence (CPL).