51

Original Research Paper

J. Jpn. Soc. Colour Mater., 90〔2〕，51–60（2017）

Synthesis and Luminescence Properties of Dithieno[3,2-a:2’,3’-c]Phenazine Derivatives
with Electron-Donating π-Conjugated Side-Arms at the 2, 5- and 8, 11-Positions
Yanjun He＊, Natsuki Okamoto＊, Takeshi M aeda＊, Hiroyuki Nakazumi＊ and Shigeyuki Yagi＊,†＊ Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University,

1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan†Corresponding Author, E-mail: yagi@chem.osakafu-u.ac.jp(Received July 7, 2016; Accepted October 12, 2016)
Abstract
Two types of novel dithieno[3,2-a:2’,3’-c]phenazine (dtpz) derivatives, bearing electron-donating π-conjugated side-arms at the 2,5- and8,11-positions, were synthesized and their luminescence properties were discussed. The 8,11-disubstituted derivatives exhibited fluorescencein dichloromethane in the regions from yellow to red (photoluminescence wavelength λPL; 557–651 nm). Especially, 9-(2-ethylhexyl)9H-carbazol-3-yl and 4-hexylthiophen-2-yl side-arms afforded red emission with high photoluminescence quantum yields (ΦPL) of 0.75(λPL; 616 nm) and 0.38 (λPL; 651 nm), respectively. Although the 2,5-disubstituted derivatives (λPL; 630–685 nm) exhibited more redshifted fluorescence in dichloromethane than the 8,11-disubstituted derivatives, they are less emissive, showing ΦPL of 0.07–0.23. All thedeveloped dtpz derivatives showed positive solvatochromic behavior in photoluminescence, and red shifts of their photoluminescence spectra
were observed as polarity of the solvent increased. From the Lippert-Mataga plots, their dipole moments were significantly enlarged upon
photoexcitation, indicating that strong intramolecular charge transfer occurs upon electronic transition. Using the 8,11-disubstituted dtpz
derivative with 9-(2-ethylhexyl)-9H-carbazol-3-yl side-arms as an emitting dopant, a poly(9-vinyl-9H-carbazole) (PVCz)-based OLED
was fabricated. Yellow electroluminescence with the Commission Internationale de L’éclairage chromaticity coordinate of (0.53, 0.46) was
observed, the spectrum of which was blue-shifted in comparison with photoluminescence of the emitting dopant in dichloromethane due tolow polarity of the PVCz host.
Key-words: Dithieno[3,2-a:2’,3’-c]phenazine, Fluorescence, Intramolecular charge transfer transition, Solvatochromism,Organic light-emitting diode( dbpz ) 16,17) platforms, where π-based electron-donatinggroups at the 10,13-positions gave rise to intense PL basedon the intense ICT transition. In the case of the dppz-baseddyes, the emission color was tuned from greenish blue to
red partially with the help of metal coordination, whererelatively high PL quantum yields were achieved15). We also
reported that the introduction of fluorene side-arms to dbpz
yielded highly emissive green fluorophores, and therein we
demonstrated the fabrication of OLEDs using these dyes
as an emitting dopant16). Furthermore, the dbpz derivatives
bearing π-extended electron-donating side-arms showed redshifted emission from red to deep red17).
Here we report synthesis and PL properties of novel
fluorescent dyes based on a dithieno[3,2-a:2’,3’-c]phenazine(dtpz) skeleton appended with electron-donating side-arms
at the 8,11- or 2,5-positions, namely 1 and 2, respectively( Fig. 1 ) . Although several dtpz-containing low-mass
molecules and polymers have so far been developed aimed
at development of organic semiconductors and photovoltaicmaterials 18,19 ) , there have been few reports on the PL
properties of dtpz derivatives20). In the dtpz building block,the fused thiophene rings and the phenazine moiety act as

1．Introduction
Fluorescent dyes have so far been frequently utilizedin various fields1-5), and especially in the field of organic
electronics such as organic light-emitting diodes (OLEDs),highly fluorescent molecules are intensely required because
the photoluminescence (PL) quantum yield of the emitter is
one of the factors determining the quantum efficiency of thedevice6). To modulate the emission color purposively, various
kinds of fluorescent dyes have been eagerly developedon the basis of donor-acceptor (D-A) electronic structures
because controlling the intramolecular charge transfer (ICT)transition allowed us to tune the singlet excitation energy ofa fluorophore7-10). As electron-donating π-building blocks,
electron-rich aromatic components such as arylamines andcarbazole derivatives have been frequently used8,9,11,12).
As for electron-withdrawing π-building blocks, electrondeficient frameworks such as 2,1,3-benzothiadiazole,dibenzo[b,d]thiophene S,S-dioxide, and other heterocycles
have been used8,13,14). Recently we have developed novel
fluorophores based on electron-deficient dipyrido [ 3,2a:2’,3’-c]phenazine (dppz)15) and dibenzo[a,c]phenazine－1－© 2017 Journal of the Japan Society of Colour Material