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

Umamahesh Balijapalli; Masaki Tanaka; Morgan Auffray; Chin-Yiu Chan; Yi-Ting Lee; Youichi Tsuchiya; Hajime Nakanotani; Chihaya Adachi

doi:10.1021/acsami.9b20020

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

ACS Appl Mater Interfaces. 2020 Feb 26;12(8):9498-9506. doi: 10.1021/acsami.9b20020. Epub 2020 Feb 14.

Authors

Umamahesh Balijapalli¹, Masaki Tanaka¹, Morgan Auffray¹, Chin-Yiu Chan¹, Yi-Ting Lee¹, Youichi Tsuchiya^{1

2}, Hajime Nakanotani^{1

2}, Chihaya Adachi^{1

2}

Affiliations

¹ Center for Organic Photonics and Electronics Research (OPERA) , Kyushu University , 744 Motooka , Nishi, Fukuoka 819-0395 , Japan.
² International Institute for Carbon Neutral Energy Research (WPI-I2CNER) , Kyushu University , 744 Motooka , Nishi, Fukuoka 819-0395 , Japan.

PMID: 32020791
DOI: 10.1021/acsami.9b20020

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 (τ_d) 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.

Keywords: OLED; TADF; bluish-green emission; delay lifetime; multidonor; pentacarbazole; roll-off behavior.