Helical Oligophenylene Linked with [2.2]Paracyclophane: Stereogenic π‐Conjugated Dye for Highly Emissive Chiroptical Properties

• Published in: Chemistry : a European journal Vol. 27; no. 65; pp. 16225 - 16231
• Main Authors: Hasegawa, Masashi, Ishida, Yuki, Sasaki, Hiroaki, Ishioka, Sumire, Usui, Kazuteru, Hara, Nobuyuki, Kitahara, Maho, Imai, Yoshitane, Mazaki, Yasuhiro
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 22.11.2021
• Subjects: Chemistry; Chemistry, Multidisciplinary; circularly polarized luminescence; cyclophane; macrocycle; oligoparaphenylene; Physical Sciences; Science & Technology; CIRCULARLY-POLARIZED LUMINESCENCE; OPTICAL RESOLUTION; cyclophane; macrocycle; oligoparaphenylene; PLANAR; circularly polarized luminescence; CHIRALITY
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202103158

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 CH2Cl2 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 (|gCPL|=1.6×10−3) in circularly polarized luminescence (CPL). Helical oligophenylene: Chiral cyclic homologues with unique structures such as double helices and twisted triangles, have been synthesized as highly emissive chiroptical dyes. The twisted quaterphenyl units exhibited CPL with a high quantum yield (0.73–0.80), leading to relatively high CPL brightness.