No abstract

The excited-state dynamics of polysilane dendrimers are studied using time-resolved emission spectroscopy. The time-resolved emission spectra of polysilane dendrimers showed two bands, one in the UV and one in the visible region. The former was assigned to the emission from the excited state at the linear Si-Si chain, and the latter was assigned to that at the branching points. The intramolecular energy transfer between both excited states was demonstrated by the emission time profile, which showed a growth in intensity with increase in the delay time after laser excitation. The spectral shape of the visible emission can be expressed by a fitted curve using a Gaussian distribution function, which suggests that the configuration coordinates model is applicable to the photophysical processes of a Si-Si chain with a branching point. An MO calculation showed the distorted geometry around the branching point in the excited state, which corresponds to the localized excited state in the configuration coordinates model.

No abstract

An electron-transporting 2,5-bis(4-bromophenyl)-1,3,5-oxadiazole (OXD) was incorporated by copolymerization into polyfluorene (PF) end-capped with a 4-bromo-4',4"-dimethyltriphenylamine (TPA) main chains on the Yamamoto coupling method to improve the initial electroluminescence (EL) color stability against applied voltage and the device operation lifetime. The copolymer, PF/OXD-TPA, possessed a high molecular weight enough for film-forming ability and excellent solution-processability, that is, good solubility in common organic solvents such as toluene. An EL device fabricated using this copolymer as a polymeric emission layer allowed the generation of a strong deep-blue EL peaking at 424 nm with a comparatively high EL efficiency of 0.47 cd A -1, and its color was extremely stable against applied voltage within 527 V. The incorporation of OXD units into the PF-TPA system also improved the operation lifetime, although it is not a practical level for displays. The results are probably attributed to the great roles of the incorporated OXD units for disturbing the formation of fluorene excimer sites and for tuning the hole/electron mobility balance..