Nobuhiko Akino1,Emiri Kato1,Ryoichi Ishimatsu2,Jun Mizuno3,Takashi Kasahara1
Hosei University1,University of Fukui2,National Cheng Kung University3
Nobuhiko Akino1,Emiri Kato1,Ryoichi Ishimatsu2,Jun Mizuno3,Takashi Kasahara1
Hosei University1,University of Fukui2,National Cheng Kung University3
Recently, electrogenerated chemiluminescence or electrochemiluminescence (ECL) cells have been considerable attention for the use in future displays due to their simple device structure and also easy fabrication process.[1,2] In the previous study, we have shown that the ECL performances of 5,6,11,12-tetraphenyltetracence(rubrene)-based device was significantly improved by using 4-(di-<i>p</i>-tolylamino)-4’[(di-<i>p</i>-tolylamino)styryl]stilbene (DPAVB) as an emitting assist dopant, compared with the performance of device without it.[3] For example, the maximum luminance of the device with an emitting assist dopant was improved to 292 cd/m<sup>2</sup> at 6.0 V, which is approximately 3.4 times higher than the luminance of the device without it (86.2 cd/m<sup>2</sup> at 5.5 V).<br/>From the cyclic voltammograms (CVs), both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of DPAVB are shallower than HOMO and LUMO of rubrene. Based on the energy level configuration of neutral molecules, it seems energetically unfavorable for an electron on HOMO of rubrene radical anion to DPAVB radical cation in order to form the excited states of rubrene. The mechanism of the improvement in device performance has not been clear enough and it has been desired to understand deeply for further improvements.<br/>In this study, we have utilized the quantum chemical calculations to shed some light on the mechanism in the device with an assist dopant. The geometry optimizations of molecules are performed using the density functional theory at the level of B3LYP and the solvent effects are incorporated using the polarizable continuum model (PCM). The calculated energy levels of the radical anion of rubrene and the radical cation of DPAVB are modified from the levels of the neutral molecules. Their relative positions support the energetically efficient electron transfer from the former to the latter leading to the excited states of rubrene and the neutral state of DPAVB, which results in the luminance improvement in ECL device.<br/><br/>REFERENCES<br/>[1] S. H. Kong, J. I. Lee, S. Kim, and M. S. Kang, ACS Photonics, <b>5</b>, 267 (2018)<br/>[2] T. Nobeshima, T. Morimoto, K. Nakamura, and N. Kobayashi, J. Mater. Chem., <b>20</b>, 10630 (2010)<br/>[3] E. Kato, R. Ishimatsu, J. Mizuno, and T. Kasahara, Electrochemistry, <b>91</b>(4), 047002 (2023)