We report the preparation of a new electroluminescent polymer by the oxidative coupling copolymerization of N-(4-n-butylphenyl)phenoxazine and 9,9-di-nbutylfluorene with ferric(III) chloride. The reaction yields soluble polymers with a weight-average molecular weight as high as 9000. The reactivity has been studied with respect to the reaction time, temperature, and feed ratio of the comonomers. Under optimum conditions, a copolymer with a 50% comonomer incorporation ratio can be obtained in a 75% yield. The polymers have been characterized with differential scanning calorimetry, cyclic voltammetry, and optical spectroscopy. A simple single-layer light-emitting-diode device of an indium tin oxide/polymer/Mg-Ag structure shows a luminance of 200 cd/m 2 at an 18-V operating voltage. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: [4338][4339][4340][4341][4342][4343][4344][4345] 2006

We report a study of excimer emission from copolymers of dibutylfluorene and butylphenylphenoxazine. Temperature dependence of photoluminescence (PL) spectra measured from room temperature to above glass transition temperature, and excitation power dependence of PL spectra reveal that the observed differences in excimer intensity between PL and electroluminescence spectra are neither solely due to local heating by electric current nor to differences in exciton density. Instead, different nature of the excitations upon photoexcitation and excitation by passing current has to be considered to explain the different behavior.

Artificial disturbances are introduced to a turbulent boundary layer separating at a convex corner to see how excited vortices control the turbulent separation. The results clearly show that excitation of vortices with appropriate scale can effectively suppress the separation of turbulent boundary layer, not unlike the case of laminar separation. However, strong disturbance growth due to Kelvin-Helmholtz instability, which decisively dominates development of separation bubble for laminar separation, does not occur for turbulent separation. Therefore direct excitation of energetic vortices around the separation point is required for suppression of turbulent separation.