Ambidextrous Chirality Transfer Capability from Cellulose Tris(phenylcarbamate) to Nonhelical Chainlike Luminophores: Achiral Solvent-Driven Helix-Helix Transition of Oligo- and Polyfluorenes Revealed by Sign Inversion of Circularly Polarized Luminescence and Circular Dichroism Spectra

• Published in: Biomacromolecules 2018-02, Vol.19 (2), p.449-459
• Main Authors: Guo, Sibo, Kamite, Hiroki, Suzuki, Nozomu, Wang, Laibing, Ohkubo, Asuka, Fujiki, Michiya
• Format: Article
• Language: English
• Subjects: Cellulose - chemistry; Circular Dichroism; Fluorenes - chemistry; Isomerism; Luminescence; Phenylcarbamates - chemistry
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/acs.biomac.7b01554

We investigated whether helicity and/or chirality of cellulose tris­(phenylcarbamate) (CTPC) can transfer to noncharged, nonhelical oligo- and polyfluorenes when CTPC was employed as a solution processable homochiral platform of a D-glucose-skeletal polymer. Noticeably, CTPC revealed the solvent-driven, ambidextrous intermolecular helicity/chirality transfer capability to these fluorenes. The chiroptical inversion characteristics of circularly polarized luminescence (CPL) and the corresponding CD spectra were realized by solely choosing a proper achiral solvent and/or achiral cosolvent. When the solution of PF6 and CTPC in tetrahydrofuran (THF) was cast on a quartz substrate, the dissymmetry ratio of CPL (g CPL) from the polymer film showed g CPL = +2.1 × 10–3 at 429 nm. Conversely, when dichloromethane (DCM) was used as the solvent, the CPL sign was inverted to g CPL = −2.4 × 10–3 at 429 nm. The dissymmetry ratio of Cotton CD band (g CD) from the THF solution was g CD = +3.2 × 10–3 at 392 nm; conversely, from the DCM, the CD sign inverted to g CD = −0.8 × 10–3 at 371 nm. The sign and magnitude of the g CD values were interpreted to a London dispersion term (δd) of Hansen solubility parameter (δ) of the casting solvents rather than a dipole–dipole interaction term (δp) and a hydrogen bonding interaction term (δh) of the δ values and dielectric constant (ε). Analysis of solvent-driven changes in FTIR spectra, wide-angle X-ray diffraction profiles, and differential scanning calorimetry diagrams indicated that solvent driven on–off switching of multiple hydrogen bonds due to three urethane groups of CTPC play the key for the inversion. Intermolecular CH/π and π–π interactions among phenyl rings and alkyl groups were assumed to be crucial for helicity/chirality transfer capability based on molecular mechanics and molecular dynamics simulations of PF6–CTPC hybrids. These chiroptical inversion characteristics arose from solvent-driven order–disorder transition characteristics of the CTPC helix rather than a helix–helix transition of CTPC itself.