Highly luminescent π-conjugated polymeric microspheres were fabricated through self-assembly of energy-donating and energy-accepting polymers and their blends. To avoid macroscopic phase separation, the nucleation time and growth rate of each polymer in the solution were properly adjusted. Photoluminescence (PL) studies showed that efficient donor-to-acceptor energy transfer takes place inside the microspheres, revealing that two polymers are well-blended in the microspheres. Focused laser irradiation of a single microsphere excites whispering gallery modes (WGMs), where PL generated inside the sphere is confined and resonates. The wavelengths of the PL lines are finely tuned by changing the blending ratio, accompanying the systematic yellow-to-red color change. Furthermore, when several microspheres are coupled linearly, the confined PL propagates the microspheres through the contact point, and a cascade-like process converts the PL color while maintaining the WGM characteristics. The self-assembly strategy for the formation of polymeric nano- to microstructures with highly miscible polymer blends will be advantageous for optoelectronic and photonic device applications.

A plasma enhanced vapor deposition process is used to synthesize graphene from a hydrogen/methane gas mixture on copper samples. The graphene samples were transferred onto SiO2 substrates and characterized by Raman spectroscopic mapping and atomic force microscope topographical mapping. Analysis of the Raman bands shows that the deposited graphene is clearly SLG and that the sheets are deposited on large areas of several mm2. The defect density in the graphene sheets is calculated using Raman measurements and the influence of the process pressure on the defect density is measured. Furthermore the origin of these defects is discussed with respect to the process parameters and hence the plasma environment.

Stille-coupling of carboxylate-substituted dibrominated benzodithiophene (BDTC) with 2,5-distannylthieno- [3,4-b]thiophene gave novel donor−acceptor type alternating copolymers, PBDTC-TT, where BDTC works as an electronaccepting unit in the polymers. They showed broad absorption bands from 500 nm to the near-infrared region, optical band gap (E g ) about 1.5 eV, small π-stacking distance (3.6 Å), and good thermal stability. The hole mobilities of PBDTC-TT determined from performance of their organic field-effect transistors were 3.1−6.9 × 10 −4 (cm 2 V −1 s −1 ). The bulk heterojunction (BHJ) solar cells were fabricated with configuration of ITO/PEDOT:PSS/polymer:PC 70 BM/LiF/ Al. A PBDTC-TT device exhibited photocurrent response upon exposure to light with wavelength of 300−900 nm and incident photon to current conversion efficiency over 40% in the range of 400−750 nm. The power conversion efficiency of the best-performed device reached 3.03% with short-circuit current density of 12.54 mA cm −2 , fill factor of 0.48, and open circuit voltage of 0.51 V under illumination of AM 1.5 G/100 mW cm −2 . These results show that the BDTC unit can behave as an electron accepting building block for donor−acceptor type narrow band gap polymers, and these types of polymers can be used as a donor material in the active layer for BHJ photovoltaic cells.

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N-Alkyl and N-phenyl substituted poly(carbazole)s having a 4,5-ethenylene bridge, poly(4H-benzo[def]carbazole)s, were newly synthesized. Poly(carbazole)s having a 4,5-ethylene bridge were also synthesized for comparison. They were prepared from corresponding dibromo monomers by Ni(0)-catalyzed Yamamoto polycondensation. All the polymers had good solubility in common organic solvents, enough high molecular weights to make thin films, and good thermal stability showing about 400 °C of temperature at 5 wt% loss in TGA. The band gaps of these polymers were in the range of 2.77-3.15 eV which were appropriate for bluish light emissions. The absorption and emission maxima of these polymers in CHCl3 were in the ranges of 361-396 and 419-456 nm, respectively. These polymers showed good fluorescence quantum efficiencies in CHCl3. The energy levels of highest occupied molecular orbital of the poly(benzocarbazole)s were shallower than those of corresponding 4,5-ethylene bridged poly(carbazole)s.