Asymmetrically 2,7-difunctionalized carbazole-based donor-acceptor hybrids for deep blue electroluminescence applications

Asymmetrically 2,7-difunctionalized carbazoles decorated with cyano group and different conjugated chromophores have been synthesized by following Suzuki coupling reactions. Direct C-C coupling between cyanocarbazole and peripheral chromophores lead to twist structure of the molecules. As a result, it restricts the electronic communication between the chromophores and thereby confines absorption and emission maxima in shorter wavelength region. The positive solvatochromic emission spectrum of carbazole and triphenylamine substituted compounds is ascribed to synergistic effect of large structural reorganization and intramolecular charge transfer at excited state. Density functional theory (DFT) studies reveal the involvement of ICT from donor carbazole/triphenylamine to cyanocarbazole acceptor. OLED device containing a pyrene substituted dye (5 wt% in CBP host) displayed deep blue electroluminescence with the EQE of 3.0% and CIE of (0.16, 0.06). The superior device performance can be attributed to favorable energy level alignment of this dye with CBP host and complete energy transfer from the host to guest.