Electrochemiluminescence (ECL) is a light emitting phenomenon of excited species which is generated from electrochemical reaction at electrodes. ECL reaction has attracted great interest to utilize as the novel kinds of light emitting devices. We have reported that the ECL device can be integrated with reflective displaying devices based on liquid crystal^[1] or organic electrochromic^[2] technologies. Moreover, the ECL emission colors from the ECL electrolyte solution dissolving 9, 10-diphenylanthracene (DPA) and rubrene in N-methyl-2-pirroridone (NMP) can be controlled by changing the frequency of alternating current (AC) voltage.^[3]

Here, we focused on the blue emission of AC-driven ECL (AC-ECL) systems because the ECL intensity and long-term stability were unsatisfactory in present stage. One of the reasons for the issue is that the balance of redox species in the device did not exactly match. In this study, we introduced mixed solvent of propylene carbonate (PC)-toluene system (volume ratio = 1:1) for achieving the stable blue ECL from DPA molecule. PC is well known as the electrochemically stable solvent; toluene can also dissolve the large amount of aromatic compound such as DPA. We measured the electrochemical and optical properties of the DPA in NMP or PC/toluene electrolyte solution in order to discuss the effect of stabilities of redox species on the AC-ECL properties. As a result, it was found that the composition of electrolyte affected the stability of oxidized and reduced species. Moreover, the emission properties of the AC-ECL device were strongly depended on the stability of redox species. From these results, to achieve the good performance of the blue ECL device, it is required that the exactly matched balance of redox species in the device.

Reference

[1] S. Tsuneyasu, K. Nakamura, N. Kobayashi, Chem. Lett., 45, 949 (2016).

[2] S. Tsuneyasu, L. Jin, K. Nakamura, N. Kobayashi, Jpn. J. Appl. Phys., 55, 041601 (2016).

[3] T. Nobeshima, M. Nakakomi, K. Nakamura, N. Kobayashi, Adv. Optical Mater., 1, 144 (2013).