Effects of Functional Groups in Unsymmetrical Distyrylbiphenyl on the Performances of Blue Organic Light Emitting Diodes

The effects of derivatives in unsymmetrical distyrylbiphenyl compounds on the performance of blue organic light emitting diodes (OLEDs) were investigated. Organic compounds based on unsymmetrical distyrylbiphenyl were synthesized with respect to the numbers and locations of methyl and tert-butyl groups. The main peak wavelength of photoluminescence (PL) spectra in a solid state and the difference in the PL main peak between the solid and solution states decreased as the number of tert-butyl groups in unsymmetrical distyrylbiphenyl decreased. Furthermore, discernible diffraction peaks and roll-like grain were not observed as the number of tert-butyl groups increased, indicating that the tert-butyl group prohibits the formation of a planar structure and thus reduces chromophoric π–π interaction and fluorescence quenching. The luminance value of OLEDs used as an active layer in the tert-butyl–tert-butyl functional group was as high as 1860 cd/m2 at a current density of 150 mA/cm2 due to the reduction in fluorescence quenching. Therefore, the tert-butyl group is effective at prohibiting fluorescence quenching in distyrylbiphenyl compounds.