Masao Motonaga

Alkyl side chain effects of optically active polyfluorenes on their chiroptical absorption and emission properties

Abstract We prepared three optically active polyfluorenes (PFs), poly[2,7-{9,9-bis[(S)-2-methyloctyl]}fluorene] (S1) and poly[2,7-{9,9-bis[(S)- and/or (R)-3,7-dimethyloctyl]}fluorene] (S2 and/or R2) and an optically inactive poly[2,7-(9,9-di-n-decyl)fluorene] (3) in order to investigate the alkyl side-chain effects on their (chir)optical properties in both solution and solid states. PF S1 showed more intense circular dichroism (CD) signals in THF solution at higher and lower temperatures due to a stiffer backbone structure. Although the CD and UV–visible spectra suggested that similar thermodriven order–disorder conformational transitions occurred for all of these PFs, the highly ordered conformations formed upon cooling showed less planar structures with the stereocenters closer to the PF backbones, whose planarity decreased in the order of 3, S2/R2, and S1. In the pristine spin-coated films on quartz, with the stereocenters closer to the PF backbones, the corresponding PFs showed more intense bisignate CD signals and blueshifts in the emission peaks.

Nearly pure blue photoluminescent poly{2,7-[9-{3,5-bis[3,5-bis(benzyloxy)benzyloxy]benzyl}-9 -(3,6-dioxaoctyl)]fluorene} in filmElectronic supplementary information (ESI) available: characterization data for 2, 3, and 4, and measurement details of the quantum yield in THF solution. See http://www.rsc.org/suppdata/cc/b1/b108097k/

The first unsymmetrically substituted polyfluorene bearing a bulky poly(benzyl ether) dendron and less bulky 3,6-dioxaoctyl groups in the 9-position was designed and synthesized, which gives almost a pure bluish photoluminescence with negligible weak greenish excimer emission around 520 nm even in a thermally annealed thin solid film.

Thermo-driven chiroptical switching polysilane featuring 2-cyclopentylethyl side group

A new rod-like helical polysilane, poly{(S)-3,7-dimethyloctyl-(2-cyclopentylethyl)silane}, was found to undergo a thermo-driven, helix-helix transition at –33 ° C in isooctane associated with the discontinuous changes in the Siσ -Siσ *transition energy and intensity in the transition temperature region. This is the first example of a helix-helix transition polysilane with a cycloalkyl group. A similar rod-like polysilane derivative, poly{(S)-3,7-dimethyloctyl-(1-cyclopentylmethyl)silane}, however, did not undergo any helix-helix transition between –61 and 80 ° C.

Temperature-dependent helix-helix transition of an optically active poly (diarylsilylene)

The poly(diarylsilylene) copolymer mainchain helix in (Ar*2Si)x(Ar2S i)1−x [Ar* = 3-(S)-2-methylbutylphenyl, Ar = 4-butylphenyl, x = 0.2] undergoes a thermally driven inversion of helical screw sense with a transition temperature of −10 °C.