New fluorene-based chiral copolymers with unusually high optical activity in pristine and annealed thin films

Cho, Min Ju; Ahn, Jong Soo; Kim, Young Un; Um, Hyun Ah; Prasad, Paras N.; Lee, Geon Joon; Choi, Dong Hoon

doi:10.1039/c5ra26523a

Cited by 18 publications

(30 citation statements)

References 21 publications

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“…1000 mdeg, see the black line in the inset of Fig. 5) 21,42 arises from the cholesteric arrangement of the polymer chains 43–45 . The CD spectrum of the polymer will also experience a pressure-induced periodic shift because of the propagation of the acoustic phonon inside the film.…”

Section: Resultsmentioning

confidence: 99%

“…The synthesis and characterization of the chiral PFPh and PFBT were described recently 21 . Cholesteric copolymer thin films were produced by spin-coating a filtered 7.5 mg ml −1 solution of each polymer in a chlorobenzene-chloroform mixture (1:9 by volume) on thoroughly cleaned and ozonized Duran glass slides (thickness 1 mm) for one minute at 1000 or 500 rpm, respectively.…”

Section: Methodsmentioning

confidence: 99%

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Coherent acoustic phonon dynamics in chiral copolymers

Scholz

Morgenroth

Lenzer

2019

Structural Dynamics

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Coherent phonon oscillations in the UV-Vis transient absorption and circular dichroism response of two chiral polyfluorene-based copolymer thin films are investigated. A slow oscillation in the hundred picosecond regime indicates the propagation of a longitudinal acoustic phonon with a frequency in the gigahertz range through cholesteric films of PFPh and PFBT, which allow for the optical determination of the longitudinal sound velocity in these polymers, with values of (2550 ± 140) and (2490 ± 150) m s−1, respectively. The oscillation is induced by a strain wave, resulting in a pressure-induced periodic shift of the electronic absorption bands, as extracted from a Fourier analysis of the transient spectra. The acoustic phonon oscillation is also clearly detected in the transient circular dichroism (TrCD) response of PFPh, indicating a transient pressure-induced shift of the CD spectrum and possibly also phonon-induced chirality changes via pitch length modulation of the cholesteric helical polymer stack.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Coherent acoustic phonon dynamics in chiral copolymers

Scholz

Morgenroth

Lenzer

2019

Structural Dynamics

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“…Intrinsically chiral PFBT (c-PFBT) copolymer with a number average molar weight ( M n ) of 7.46 kg mol −1 and polydispersity (PDI) of 2.44 was prepared via Suzuki polycondensation from 2,7-bispinacoyl-9,9-bis(( S )-3,7-dimethyloctyl)fluorene boronic ester, 3,6-dibromothiadiazole and 2-pinacoyl-9,9-bis(( S )-3,7-dimethyloctyl)fluorene boronic ester and then purified afterwards 17 , 18 . A solution of c-PFBT in a chlorobenzene:chloroform mixture (1:9 by volume, concentration 7.5 mg ml −1 ) was spin-coated on thoroughly cleaned 1 mm-thick borosilicate glass slides.…”

Section: Methodsmentioning

confidence: 99%

Mapping the broadband circular dichroism of copolymer films with supramolecular chirality in time and space

et al. 2022

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Measurements of the electronic circular dichroism (CD) are highly sensitive to the absolute configuration and conformation of chiral molecules and supramolecular assemblies and have therefore found widespread application in the chemical and biological sciences. Here, we demonstrate an approach to simultaneously follow changes in the CD and absorption response of photoexcited systems over the ultraviolet−visible spectral range with 100 fs time resolution. We apply the concept to chiral polyfluorene copolymer thin films and track their electronic relaxation in detail. The transient CD signal stems from the supramolecular response of the system and provides information regarding the recovery of the electronic ground state. This allows for a quantification of singlet−singlet annihilation and charge-pair formation processes. Spatial mapping of chiral domains on femtosecond time scales with a resolution of 50 μm and diffraction-limited steady-state imaging of the circular dichroism and the circularly polarised luminescence (CPL) of the films is demonstrated.

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“…On the other hand, Chen and co-workers have shown that chiral oligo(fluorenes) , exhibit highly ordered chiral liquid crystalline phases such as cholesterics in annealed films with g -values >0.1. The cholesteric ordering has been mainly observed for poly(fluorene) homopolymers, , copolymer, − and poly( p -phenyleneethynylene)s which exhibited g -values ranging from 0.1 to 1 in annealed thin-films. Unlike the metal complexes discussed previously, the chiral poly(fluorene)s , and poly(thiophene)s show a strong film-thickness dependence of g abs , indicating that the long-range cholesteric ordering dictates the g -value in such systems.…”

Section: Introductionmentioning

confidence: 99%

Amplifying Chiroptical Properties of Conjugated Polymer Thin-Film Using an Achiral Additive

et al. 2018

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Chiral conjugated polymers bearing enantiopure side chains offer the possibility to harness the effect of chirality in organic electronic devices. However, its use is hampered by the low degree of circular polarization in absorption (gabs) in most of the conjugated polymer thin-films studied. Here we demonstrate a versatile method to significantly increase the gabs by using a few weight percentages of a commercially available achiral long-chain alcohol as an additive. This additive enhances the chiroptical properties in both absorption and emission by ca. 5–10 times in the thin-films. We envisage that the alcohol additive acts as a plasticizer which enhances the long-range chiral liquid crystalline ordering of the polymer chains, thereby amplifying the chiroptical properties in the thin-film. The application of this methodology to various conjugated polymers has been demonstrated.

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New fluorene-based chiral copolymers with unusually high optical activity in pristine and annealed thin films

Abstract: Polyfluorene (PF)-based chiral alternating copolymers, i.e., PFPh and PFTh, were successfully synthesized to obtain high circular dichroism (CD) in pristine thin films.

Cited by 18 publications

References 21 publications

Coherent acoustic phonon dynamics in chiral copolymers

Coherent acoustic phonon dynamics in chiral copolymers

Mapping the broadband circular dichroism of copolymer films with supramolecular chirality in time and space

Amplifying Chiroptical Properties of Conjugated Polymer Thin-Film Using an Achiral Additive

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