Molecular engineering of pyrimidine-containing thermally activated delayed fluorescence emitters for highly efficient deep-blue (CIEy < 0.06) organic light-emitting diodes

Abstract

The development of efficient and robust, deep-blue, thermally activated delayed fluorescence (TADF) emitters, especially those matching the European Broadcasting Union (EBU) standard with Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.06), is one of the challenging issues in organic light-emitting devices (OLEDs). Through sophisticated molecular engineering, two novel pyrimidine derivatives with D-π-A configuration, 5-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (pBFCz-26DPPM) and 5-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-5H-benzo [4,5]thieno[3,2-c]carbazole (pBTCz-26DPPM) have been designed and synthesized. There are only negligible differences in the molecular configuration and thermal, electrochemical and photophysical properties for the two compounds. However, TADF properties can be tuned by changing the heteroatom in the donor moiety. Compound pBFCz-26DPPM offers a shorter delayed fluorescence lifetime (τd) than that of pBTCz-26DPPM. The optimized device serving pBFCz-26DPPM as dopant presents deep-blue Commission Internationale de l’Eclairage (CIE) coordinates of (0.154, 0.054) and maximum external quantum efficiencies (EQEmax) of 6.20%. Remarkably, no-doped device based on pBFCz--26DPPM delivers CIE coordinates of (0.153, 0.067) and EQEs as high as 5.80%. These device performances are amongst some of those of the best performing deep blue TADF OLEDs with similar color gamut.