A new POSS (polyhedral oligomeric silsesquioxane)-substituted polyfluorene was synthesized from the nickel-catalyzed Yamamoto coupling reaction. The synthesized polymers could be well characterized by 1 H NMR, FT-IR, and elemental analysis. PL spectra of PFPOSSs on the quartz film showed reduced aggregation/excimer formation because the bulky POSS group prohibited interchain interactions. This effective dilution effect and the high thermal stability of the POSS unit also improved the color stability of PFPOSSs blue emission even after thermal annealing at 150 °C. The fluorescence quantum yields (Φ FL) of PFPOSSs in both solution and solid state were higher than those of poly(dialkylfluorene)s. Moreover, the ITO/PEDOT-PSS/polymer/Ca/Al LED device using this polymer as emitting layer showed a very stable blue light emission. LED devices of PFPOSSs showed a low turn-on voltage of 3.7-4.4 V, high brightness of 350-1010 cd/m 2 , and external efficiencies of 0.11-0.36%.

The first novel polyfluorene copolymers containing siloxane bridges were synthesized by Ni(0)-mediated copolymerization between 2,7-dibromo-9,9′-dihexylfluorene and a bridged fluorene monomer containing siloxane linkages. Two such bridged copolymers were prepared: PSiloBg1 (containing 1 mol % siloxane-bridged fluorene unit) and PSiloBg3 (containing 3 mol % siloxane-bridged fluorene unit). PSiloBg1 and PSiloBg3 exhibited good solubility in common organic solvents, thermal stability up to 420°C, and facile film formation. The glass transition temperatures of the bridged polymers (106 and 110°C , respectively) were higher than that of the homo poly(dihexylfluorene) (PDHF). In particular, PSiloBg3 exhibited a polymerization yield (96%) and a molecular weight (MW ) 185 000) higher than those of PDHF (polymerization yield ) 62%, MW ) 82 000). Interestingly, after the bridged polymers had been annealed at 150°C for 4 h in air, their PL spectra showed no significant increase in vibronic structures at 450 and 475 nm and no evidence of aggregation formation and excimers at wavelengths of >500 nm. In addition, the full width at half-maximum (fwhm) of the bridged polymers was very small (fwhm ) 51-52 nm) compared to that of PDHF (fwhm ) 85 nm). Collectively, the results show that the polyfluorenes with siloxane bridges exhibit thermally stable almost pure blue emission, making these polymers promising candidate materials for device applications.

Two novel organic-inorganic hybrid polyfluorene derivatives, poly{(9,9 0dioctyl-2,7-fluorene)-co-(9,9 0 -di-POSS-2,7-fluorene)-co-[2,5-bis(octyloxy)-1,4-phenylene]} (PFDOPPOSS) and poly{(9,9 0 -dioctyl-2,7-fluorene)-co-(9,9 0 -di-POSS-2,7-fluorene)-co-bithiophene} (PFT2POSS), were synthesized by the Pd-catalyzed Suzuki reaction of polyhedral oligomeric silsesquioxane (POSS) appended fluorene, dioctyl phenylene, and bithiophene moieties. The synthesized polymers were characterized with 1 H NMR spectroscopy and elemental analysis. Photoluminescence (PL) studies showed that the incorporation of the POSS pendant into the polyfluorene derivatives significantly enhanced the fluorescence quantum yields of the polymer films, likely via a reduction in the degree of interchain interaction as well as keto formation. Additionally, the blue-light-emitting polyfluorene derivative PFDOPPOSS showed high thermal color stability in PL. Moreover, single-layer light-emitting diode devices of an indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/ Al configuration fabricated with PFDOPPOSS and PFT2POSS showed much improved brightness, maximum luminescence intensity, and quantum efficiency in comparison with devices fabricated with the corresponding pristine polymers PFDOP and PFT2. In particular, the maximum external quantum efficiency of PFT2POSS was 0.13%, which was twice that of PFT2 (0.06%), and the maximum current efficiency of PFT2POSS was 0.38 cd/A, which again was twice that of PFT2 (0.19 cd/A). a Film fluorescence quantum yield measured on a quartz plate with respect to poly(9,9 0dihexylfluorene), with 1.00 assumed for comparison (1 wt% in p-xylene).b Calculated from the onset values of the absorption spectra of the spin-coated films on quartz.2950 LEE ET AL.

We report here the synthesis via Suzuki polymerization of two novel alternating polymers containing 9,9‐dioctylfluorene and electron‐withdrawing 4,4′‐dihexyl‐2,2′‐bithiazole moieties, poly[(4,4′‐dihexyl‐2,2′‐bithiazole‐5,5′‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PHBTzF) and poly[(5,5′‐bis(2″‐thienyl)‐4,4′‐dihexyl‐2,2′‐bithiazole‐5″,5″‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PTHBTzTF), and their application to electronic devices. The ultraviolet–visible absorption maxima of films of PHBTzF and PTHBTzTF were 413 and 471 nm, respectively, and the photoluminescence maxima were 513 and 590 nm, respectively. Cyclic voltammetry experiment showed an improvement in the n‐doping stability of the polymers and a reduction of their lowest unoccupied molecular orbital energy levels as a result of bithiazole in the polymers' main chain. The highest occupied molecular orbital energy levels of the polymers were −5.85 eV for PHBTzF and −5.53 eV for PTHBTzTF. Conventional polymeric light‐emitting‐diode devices were fabricated in the ITO/PEDOT:PSS/polymer/Ca/Al configuration [where ITO is indium tin oxide and PEDOT:PSS is poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid)] with the two polymers as emitting layers. The PHBTzF device exhibited a maximum luminance of 210 cd/m2 and a turn‐on voltage of 9.4 V, whereas the PTHBTzTF device exhibited a maximum luminance of 1840 cd/m2 and a turn‐on voltage of 5.4 V. In addition, a preliminary organic solar‐cell device with the ITO/PEDOT:PSS/(PTHBTzTF + C60)/Ca/Al configuration (where C60 is fullerene) was also fabricated. Under 100 mW/cm2 of air mass 1.5 white‐light illumination, the device produced an open‐circuit voltage of 0.76 V and a short‐circuit current of 1.70 mA/cm2. The fill factor of the device was 0.40, and the power conversion efficiency was 0.52%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1845–1857, 2005

A new series of highly bright and efficient poly(p-phenylenevinylene)s (PPV)s based on polyhedral oligomeric silsesquioxanes (POSSs) was synthesized via the Gilch polymerization method. The three POSScontaining PPVs are as follows: POSS05-PPV(containing 5 mol % POSS-appended PPV units), POSS25-PPV, and POSS100-PPV (this is the first π-conjugated polymer composed of 100 mol % POSSs-appended repeating units). These polymers were found to be completely soluble in common organic solvents, and homogeneous thin films of these polymers were fabricated easily by spin-coating onto the quartz glasses and indium tin oxide (ITO) substrates. The POSS-containing PPVs exhibit higher glass transition temperatures (64-77°C) than that of MEH-PPV (58°C), indicating that electroluminescence (EL) devices fabricated with these polymers should have good thermal stabilities. The presence of the POSSs in the PPV side chains was found to result in the lowering of the maximum wavelengths of the UV-vis absorption and photoluminescence (PL) spectra, which occurs because of the nanosize effect of the POSS moieties appended to the polymer backbones. As the POSS content ratio in the polymers increases, the maximum wavelengths of the UV-vis absorption and PL emission spectra are increasingly blue-shifted except for those of POSS05-PPV. Light-emitting diodes (LEDs) with the configuration of ITO/ PEDOT:PSS/polymer/Ca/Al were fabricated using the novel POSS-containing PPVs. The LED devices based on the POSS-containing PPVs were found to exhibit maximum EL wavelengths ranging from 577 to 543 nm (POSS05-PPV, 577 nm; POSS25-PPV, 575 nm; and POSS100-PPV, 543 nm). The LED devices containing POSS05-PPV or POSS25-PPV emitted orange-red light, whereas that containing POSS100-PPV emitted yellow-orange light. Interestingly, the maximum brightness and luminance efficiency of the POSS25-PPV device were found to be up to 6340 cd/m 2 at 13.2 V and 0.26 cd/A at 6190 cd/m 2 , respectively, which are higher maximum brightness and luminance efficiencies than those of the MEH-PPV device (3880 cd/m 2 at 14.8 V and 0.075 cd/A at 3880 cd/m 2 ). The improvements in the EL properties of PPV derivatives that result from the introduction of the POSS moieties into the PPVs and the contribution of the POSS moieties to the conjugated polymer matrixes of EL devices were also reproduced in binary blend systems composed of a POSS-containing PPV (POSS25-PPV) and MEH-PPV. Surprisingly, the luminescence efficiency (0.48 cd/A at 10540 cd/m 2 ) of the binary blend consisting of 5 wt % of POSS25-PPV and 95 wt % of MEH-PPV was found to be enhanced by a factor of 6.4 with a maximum brightness of 11 010 cd/m 2 (at 14.3 V). It is likely that the enhanced device performance of POSS25-PPV and the binary blend consisting of 5 wt % of POSS25-PPV and 95 wt % of MEH-PPV are due to the formation of suitable insulation domains of the POSS moieties in the conjugated polymer matrixes, resulting in a balance of charge carriers, that is, of electrons and holes.