Near‐Infrared Circularly Polarized Luminescence through Intramolecular Excimer Formation of Oligo(p‐phenyleneethynylene)‐Based Double Helicates

• Published in: Chemistry : a European journal 2019-07, Vol.25 (39), p.9211-9216
• Main Authors: Miki, Koji, Noda, Takeru, Gon, Masayuki, Tanaka, Kazuo, Chujo, Yoshiki, Mizuhata, Yoshiyuki, Tokitoh, Norihiro, Ohe, Kouichi
• Format: Article
• Language: English
• Subjects: Anthracene; Carbon; Chemistry; chirality; Circular dichroism; Circular polarization; circularly polarized luminescence; Dichroism; Dipole moments; excimer; Excimers; helical structures; Luminescence; macrocycles; Magnetic transitions; NMR; Nuclear magnetic resonance; Strands; Tin
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201901467

Carbon‐based double helicates consisting of two anthracene‐containing oligo(p‐phenyleneethynylene) units and two flexible chiral 1,1′‐binaphthyl units or two rigid chiral 9,9′‐spirobifluorene units were developed. The curved oligo(p‐phenyleneethynylene) fragments in the double helicates were successfully constructed by tin‐mediated reductive aromatization. Helical oligo(p‐phenyleneethynylene) double strands fixed by two rigid spirobifluorene units showed little structural change under photoirradiation, thereby emitting circularly polarized luminescence (CPL) in the visible region with a high quantum yield (ΦPL=0.93). In contrast, flexible binaphthyl units induced dynamic structural change of the oligo(p‐phenyleneethynylene) luminophores under photoirradiation, leading to strong CPL (|glum|=1.1×10−2) in the near‐infrared (NIR) region. UV/Vis, circular dichroism (CD), CPL and NMR spectroscopic analyses of the binaphthyl‐hinged double helicate suggested excimer formation between two π‐conjugated strands in the excited state. Theoretical calculations highlight the importance of the tightly interlocked excimer structure of the carbon‐based double helicate in controlling the angle between the electric and magnetic transition dipole moments for strong NIR CPL generation. Open shut them: Chiral macrocycles consisting of helical oligo(p‐phenyleneacetylene) and 2,2′‐binaphthyl units form intramolecular excimers that emit near‐infrared circularly polarized luminescence with high dissymmetry factor value (see figure). Flexible chiral hinges play an important role in the formation of the tightly interlocked intramolecular excimer with a helical structure.