A new stepwise synthesis method for the preparation of precisely defined oligo(pphenyleneethynylene)s (OPEs) is described. High-purity monomer, trimer, pentamer, heptamer, and nonamer of OPEs with dihexyloxy side groups and trimethylsilyl (TMS) or thioacetyl (SAc) terminals have been synthesized. The structures of the oligomers were characterized by 1 H NMR, 13 C NMR, and elemental analysis. DSC studies show narrow and well-developed melting and crystallization peaks, indicating the high perfection of the crystals formed in these oligomers. Optical microscopy was used for investigating the supramolecular morphology of solid-state films of pentamer with TMS end groups, as an example. Numerous dendrites with a spherulitic size of ca. 50 µm were observed. UV-vis absorption and photoluminescence (PL) spectra in both dilute solution and films show a gradual red shift of the λ max from trimer to nonamer. At the nonamer stage, the optical maximum is approaching a limit of convergence.

The paper reports the first blue-light-emitting tetrahedral glass-forming molecules derived from fluorene and several tetrahedral core compounds. The glass-forming molecules (5-8) were prepared from three tetrabromo cores of X(p-ArBr) 4 (X ) C, Si; Ar ) -C 6 H 4 -, -C 6 H 4 C 6 H 4 -) and an octabromo core of tetra-(2,4-dibromobiphenyl-4′-yl)methane with 9,9-dihexylfluorene-2-MgBr via Grignard coupling reactions.Compounds 5-8 exhibited obvious glass transition behaviors with T g s in the range of 85-147 °C and displayed high thermal stabilities with T d s in the range of 329-385 °C. Compounds 5-8 exhibited strong absorptions in solution with λ max at 318-326 nm and log at 5.95-6.28. The emission maxima of these compounds in THF were in the range of 377-405 nm with high PL quantum yields of 79-100%. Under UV light excitation, their spin-coated films emitted intense blue-light peaking at 405-415 nm with quantum yields of 25-98%. The films emitted relatively pure blue light with small fwhm (full width at halfmaximum) values of 57-75 nm and absences of excimer-like long wavelength emissions, due to the nonaggregating property of the tetrahedral compounds in the solid state. The two Si-centered molecules exhibited better film-forming property and much higher film PL quantum efficiencies than their C-centered counterparts. The present tetrahedral molecules would represent a novel class of nonaggregating bluelight-emitting molecular glass-forming materials based on the fluorene fluorophore that were easily synthesized by a one-step Grignard coupling reaction.

Regioregular polymers poly(3-alkyl-2,5-thienylene-alt-1,4-phenylene) (PBTCn, n ) 4, 8, 12) and poly [1,4-bis(3-alkyl-2-thienyl)phenylene] (PBTBCn, n ) 4, 8, 12), which contain alternating phenylene and substituted thienylene or bithienylene repeating units, have been chemically and/or electrochemically synthesized and characterized. Their structures are consistent with that expected as indicated by NMR, FTIR, and microanalysis. The change in glass transition temperature and UV-vis and fluorescence spectra with modification of polymer backbone and increase of the alkyl chain length has been observed and discussed. The PBTCn series shows better thermal stability in air, and the compounds in the series are partially crystalline. The PBTCn polymers have liquid crystalline properties as shown by MDSC, XRD, and polarized optical microscopy. XPS study performed on both the neutral and doped states shows the formation of charge carrier in the polymer backbone when doped. The polymers are both p-and n-dopable as indicated by cyclic voltammetry. Electrochromism when the polymers are p-doped is also evidenced by the spectral changes in UV-vis-NIR region.

A novel regioregular polymer comprising alternating 1,4-phenylene and 3-butyl-2,5-thienylene repeat units has been synthesized and characterized using 1H NMR, FTIR, UV-VIS absorption and fluorescence emission spectroscopy. The derived polymer showed strong fluorescence with a solution quantum yield of 48% relative to quinine sulfate and a film phase photoluminescence yield of 17%. Green light-emitting diodes were fabricated using the polymer as the emitter layer.