Photon magic: chiroptical polarisation, depolarisation, inversion, retention and switching of non-photochromic light-emitting polymers in optofluidic medium. Issue 9 (23rd December 2014)

• Record Type: Journal Article
• Authors: Fujiki, Michiya; Donguri, Yuri; Zhao, Yin; Nakao, Ayako; Suzuki, Nozomu; Yoshida, Kana; Zhang, Wei
• Is Part Of: Polymer chemistry. Volume 6:Issue 9(2015)
• Page Start: 1627
• Page End: 1638
• Publication Date: 2014-12-23
• Subjects: Polymers -- Periodicals; Macromolecules -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1039/c4py01337a
• Languages: English
• ISSNs: 1759-9954

Abstract

Abstract : A circularly polarised photon hand, l - and r -, was not a deterministic factor for the induced chiroptical sign of π-conjugated polymer aggregates. This anomaly originates from circular dichroism inversion characteristics between shorter and longer π–π* bands. Abstract : Circularly polarised (CP)-photons at six different energies (six wavelengths) were irradiated to non-photochromic, highly photoluminescent poly[(9, 9-di- n -octylfluoren-2, 7-diyl)- alt -bithiophene] (PF8T2 ) as μm-sized particles in chloroform–methanol cosolvents. This approach led to the capability of photophysically controlling all chiroptical polarisation, depolarisation, inversion, retention and switching in the ground and/or photoexcited states, as proven by circular dichroism (CD), optical rotation dispersion (ORD) and circularly polarised luminescence (CPL) spectroscopy. By optofluidically tuning the refractive index of the cosolvents at 589 nm ( n D ), these CP-photon induced CD signals were resonantly enhanced at a specific n D of ≈1.40. Surprisingly, regardless of the same l - (and r -) CP hand, the choice of higher and lower CP-photon energies led to a swapping of signs in chiroptical polarisation of the particles. The CP-photon hand, l - and r -, was not a deterministic factor for the induced chiroptical sign of thePF8T2 particles. This anomaly originates from CD inversion characteristics between lower and higher energy regions, supported by ZINDO calculations ofPF8T2 model oligomers. Finally, controlled CP-photon sense and irradiating energy successfully allowed CPL-silentPF8T2 particles (quantum yield of 15%) to change to CPL-active particles of the order of | g CPL | = (1.9–4.3) × 10 −3 at ≈535 nm whilst almost keeping the quantum yield of 8%.