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

摘要

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-yObenzonitrile (pCF3BN), 2,4,6-tri(9H-carbazol9-yl)-3-(3,6-di (pyridin-3-yl)-9H-carbazol-9-yl)-5-(3,6-diphenyl9 H-c a rb azol-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-(trifluo romethyl)phenyl)-9H-carb azol-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]indo1-9-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 (tau(d)) of 4.25, 5.01, and 3.65 ps 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.