Utilization of Multi-Heterodonors in Thermally Activated Delayed Fluorescence Molecules and Their High Performance Bluish-Green Organic Light-Emitting Diodes

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 two, three, and four different types of donors, capable of bluish-green emission of around 480 nm with relatively high photoluminescence quantum yields 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 μs in their film state, respectively. Bluish-green organic light-emitting diodes based on PyPhBN, PyCF3BN, and CbPyCF3BN exhibit a high external quantum efficiency of 20.6, 19.5, and 19.6%, respectively, with unsurpassed efficiency roll-off behavior. These results indicate that the TADF properties of multidonor type molecules can be manipulated by controlling the types and number of electron donor units