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

Abstract

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) from the polymer film showed g = +2.1 × 10 at 429 nm. Conversely, when dichloromethane (DCM) was used as the solvent, the CPL sign was inverted to g = -2.4 × 10 at 429 nm. The dissymmetry ratio of Cotton CD band (g) from the THF solution was g = +3.2 × 10 at 392 nm; conversely, from the DCM, the CD sign inverted to g = -0.8 × 10 at 371 nm. The sign and magnitude of the g values were interpreted to a London dispersion term (δ) of Hansen solubility parameter (δ) of the casting solvents rather than a dipole-dipole interaction term (δ) and a hydrogen bonding interaction term (δ) 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.

Chirogenesis and Pfeiffer Effect in Optically Inactive EuIII and TbIII Tris(β-diketonate) Upon Intermolecular Chirality Transfer From Poly- and Monosaccharide Alkyl Esters and α-Pinene: Emerging Circularly Polarized Luminescence (CPL) and Circular Dichroism (CD)

“…The chirogenesis characteristics of oligo-/polyfluorenes originate from rotatable C–C bonds between fluorene rings and from C–O/C–C bonds of the cellulose derivatives ( Figure 1 ) (Guo et al, 2017 , 2018 ; Yamada et al, 2018 ) in the GS and ES because rotational barrier heights of the single bonds are as small as 1.5–2.5 kcal mol −1 . Eu III and Tb III complexes with three fod ligands should coexist as racemic mixtures of D -/ L -species of C 3 -symmetrical facial ( fac )- and C 1 -meridional ( mer ) motifs (Brittain and Richardson, 1977a ; Jalilah et al, 2018 ), while even Eu III and Tb III with three dpm should coexist as a racemic mixture of D -/ L -species of D 3 -geometry.…”

“…Note that solidified matrices are regarded as solid-like solvents with a very high viscosity. In this work, we applied a double-side, spin-coating technique (Guo et al, 2017 , 2018 ) to fabricate CPL-/CD-functioned films deposited onto fused quartz and/or borosilicate glass to obtain artifact-free CPL/photoluminescence (PL), CPLE/PL excitation (PLE), and CD/UV-visible spectra. CPL and CPL spectral characterizations of Eu III and Tb III at 4 f- 4 f transitions were assigned based on the literature (Fulgêncio et al, 2012 ; Tanner, 2013 ; Binnemans, 2015 ; de Queiroz et al, 2015 ; Xue et al, 2015 ; Yang et al, 2017 ).…”

“…These Cotton CD bands at 290 and 310 nm, however, do not originate from CABu and CTA . Broad monosignate CD bands due to n -π * transition from alkyl esters of CABu and CTA thin films appeared at ~215 nm with (+)-sign and ~205 nm with (–)-sign, respectively (Guo et al, 2018 ). These (+)-and (–)-sign CD bands at 205 and 215 nm in the solid film reflect from left-handed helicity of CABu and right-handed helicity of CTA in solutions, respectively (Dubois et al, 1998 ; Onofrei et al, 2015 ), though CABu and CTA are β-(1 → 4) linked polymers made of D -glucose framework as a common repeating unit.…”

“…The hybridized film was deposited onto a polished circular quartz plate or borosilicate glass (Tempax Float®, Schott AG. Germany) (25 mm in diameter and 1 mm in thickness) by spin coating using a spin coater (MIKASA, MS-B100, Tokyo, Japan), then, 800 μL of the solution was placed onto the center of the plate and spun at 1,500 rpm for 60 s. The films on the glass were attached on both sides (front and back surfaces) to ensure an optically symmetrical geometry with air-sample-(quartz or borosilicate substrate)-sample-air contact by spin coating chloroform or THF solutions that consist of saccharides (chiral host) and lanthanide complex (achiral guest) (Guo et al, 2017 , 2018 ; Yamada et al, 2018 ). Although the film thicknesses of both sides were not determined, we assumed to be on the order of several μm for each.…”

“…More recently, poly- and monosaccharides are excellent chiroptical platforms to generate and boost CD/CPL/circularly polarized reflection bands because of their helicoidal and cholesteric higher-order structures (Wilts et al, 2017 ; De La Cruz et al, 2018 ; Yu et al, 2018 , 2019 ; Zheng et al, 2018 ). We have proved that three cellulose derivatives (cellulose triacetate ( CTA ), cellulose acetate butyrate ( CABu ), and cellulose tris(phenyl carbamate) ( CTPC ) in Figure 1 possess an efficient ambidextrous scaffolding capability toward CD-inactive oligo- and polyfluorenes, leading to the corresponding (+)- or (–)-sign CPL-active/CD-active species as the solid film states (Guo et al, 2017 , 2018 ).…”