Synthesis of Circularly Polarized Luminescence Dyes Based on Chiral Naphthalene Oligomers

We developed four types of naphthalene oligomer-based dyes showing intense circularly polarized luminescence (CPL). (1) A peri-xanthenoxanthene (PXX) with two naphthalene rings connected via a methylenedioxy bridge and a chiral axis displayed CPL. A bridged PXX dimer also showed CPL. The bridged structure adjusts the angle between the vectors of the electric and magnetic transition dipole moments, which is essential for showing CPL activity. (2) (R,R,R)-naphthalene tetramers possessing six fluorophores displayed excimer-CPL. The fluorophores form a twist excimer. The systematic study allowed us to find an empirical rule called the excimer chirality rule: right- and left-handed excimers exhibit (+)- and (-)-CPL, respectively. (3) Pyrenes sandwiched by (R)-2-hydroxybinaphthyls exhibited solvent-dependent inversion of the sign of CPL without a change in emission wavelength. The (-)- and (+)-CPL were detected in nonpolar and polar solvents, respectively. This switching property originates from the inversion of excimer chirality caused by the presence or absence of intermolecular hydrogen bonds in the excited state. (4) A binaphthyl-bipyridyl cyclic dyad exhibited ON/OFF properties in CPL by protonation/deprotonation. The switching properties resulted from an inversion of the bipyridyl axis mediated by intramolecular hydrogen bonds.