Umamahesh Balijapalli, Masaki Tanaka, M. Auffray
Feb 5, 2020
Citations
0
Influential Citations
16
Citations
Journal
ACS applied materials & interfaces
Abstract
We report a series of pentacarbazolyl-benzonitrile derivatives such as 2,4,6-tri(9H-carbazol-9-yl)-3,5-bis(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)benzonitrile (mPyBN), 3,5-bis(3,6-bis(4-(trifluoromethyl)phenyl)-9H-carbazol-9-yl)-2,4,6-tri(9H-carbazol-9-yl)benzonitrile (pCF3BN), 2,4,6-tri(9H-carbazol-9-yl)-3-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)-5-(3,6-diphenyl-9H-carbazol-9-yl)benzonitrile (PyPhBN), 3-(3,6-bis(4-(trifluoromethyl)phenyl)-9H-carbazol-9-yl)-2,4,6-tri(9H-carbazol-9-yl)-5-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)benzonitrile (PyCF3BN), and 3-(3,6-bis(4-(trifluoromethyl)phenyl)-9H-carbazol-9-yl)-2,6-di(9H-carbazol-9-yl)-5-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)-4-(9H-pyrido[3,4-b]indol-9-yl)benzonitrile (CbPyCF3BN) in which some of the carbazoles are substituted with modified 3,5-diphenyl carbazoles exhibiting thermally activated delayed fluorescence (TADF) properties. These emitters comprised of two, three and four different types of donors, capable of bluish-green emission of around 480 nm with relatively high photoluminescence quantum yields (PLQYs) over 90% in solution. Emitters, namely, PyPhBN, PyCF3BN, and CbPyCF3BN composed of three and four different types of donors, endowed a rather short delayed lifetime (τd) of 4.25, 5.01, and 3.65 s in their film-state, respectively. Bluish-green organic light emitting diodes (OLEDs) based on PyPhBN, PyCF3BN, and CbPyCF3BN exhibits a high external quantum efficiency (EQE) of 20.6, 19.5, and 19.6%, respectively, with unsurpassed efficiency roll-off behavior. These results indicate that the TADF properties of multi-donor type molecules can be manipulated by controlling the types and number of electron-donor units.