3, 12-Dimethoxy-5, 6, 9, 10-tetrahydro-7, 8-dicyano-[5]helicene as a new emitter for blue and white organic light-emitting diodes. (January 2017)

• Record Type: Journal Article
• Authors: Sahasithiwat, Somboon; Sooksimuang, Thanasat; Kangkaew, Laongdao; Panchan, Waraporn
• Is Part Of: Dyes and pigments. Volume 136(2017)
• Page Start: 754
• Page End: 760
• Publication Date: 2017-01
• Subjects: OLEDs -- [5]helicene derivative -- Blue fluorescence material -- Exciplex -- Single crystal -- X-ray; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2016.09.042
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: In this work, crystallographic data along with thermal, electrochemical and optical properties of 3, 12-dimethoxy-5, 6, 9, 10-tetrahydro-7, 8-dicyano-[5]helicene (DTDH) were studied and reported. DTDH has an energy band gap of 2.9 eV which enable it to emit blue light in the fluorescence process. Because of high fluorescence quantum yield, i.e. 0.96, it is suitable to be used as an emissive material in an organic light-emitting diode (OLED). The device with a configuration of ITO/PEDOT:PSS/DTDH/Ca/Al emitted blue light with a peak at 475 nm. The best device showed a turn-on voltage at 4.0 V, maximum brightness at 4954 cd/m 2, and maximum current efficiency at 2.38 cd/A. However, up on mixing DTDH with N, N′-diphenyl-N, N′-bis(1-naphthyl)-1, 1′-biphenyl-4, 4′-diamine (NPB), the couple compounds form exciplex when excited resulting in a new emission spectra at lower energy with a peak at 558 nm. Consequently, White OLEDs with the configuration of ITO/NPB/NPB:DTDH(1:1)/DTDH/BCP/Alq3 /LiF/Al, in which NPB:DTDH layer was formed by co-evaporation, were fabricated. Performance and color quality of the white OLEDs can be tuned by varying thickness of the mixture layer (NPB:DTDH) and the pure DTDH layer. The best WOLED with CRI of 72 and CCT of 5096 was obtained. Evidences of exciplex formation between NPB and DTDH were observed in fluorescence lifetime and time-resolved emission spectroscopy (TRES) experiments. Graphical abstract: Highlights: Properties of a new blue emitting material, i.e. 3, 12-dimethoxy-5, 6, 9, 10-tetrahydro-7, 8-dicyano-[5]helicene (DTDH), were studied and reported. Blue OLEDs were fabricated using DTDH as an emissive material. White OLEDs were fabricated by combining emission spectra of a pure DTDH and of an exciplex between DTDH and NPB.