253

Original Research Paper

J. Jpn. Soc. Colour Mater., 91〔8〕，253–259（2018）

Crystal Structures of Dyes Composed of an Aniline Donor and a Pyrroline-Type Acceptor
Masato I mai＊,†, Shunsuke Inada＊, Yukichi Sato＊, Hiroshi K atagiri＊ and Shuji Okada＊＊＊ Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan＊＊ Graduate School of Organic Materials Science, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan†Corresponding Author, E-mail: amim3821@gmail.com(Received December 19, 2016; Accepted July 9, 2018)

Abstract
Single crystals of 3-[4-(dibutylamino)phenyl]-4-cyano-5-dicyanomethylene-2-oxo-3-pyrroline 1a and its derivatives with 1-butyl (1b),1-hexyl (1c) and 1-(2-[2-(acryloyloxy)ethoxy])ethyl (1e) groups were prepared and their X-ray crystallographic analyses were performed.
These dyes have a common π-conjugation system terminated by donor and acceptor groups, and they can be applied to use as electrooptic
chromophores. Their absorption of the crystals were discussed in relation to the chromophore alignment in the crystals. Antiparallelinteraction between the π-conjugated systems, whether face-to-face or side-by-side, caused absorption shifts to shorter wavelengths.
Absorption at the longest wavelength was observed for 1e, whose π-conjugated systems were separated by the substituents resulting in almost
no interaction among the adjacent π-conjugated systems.
Key-words: Dye, Crystal structure

The CDCOP group is a strong acceptor since three cyano andone oxo groups are conjugated in the group. Furthermore,
the CDCOP group composed of a five-membered ring
reduces steric hindrance to the linked aromatic ring,
resulting in a planar structure responsible for the fully
conjugated structure. Meanwhile, when the CDCOP dyes
were dispersed in polymer matrices, their UV-vis absorption
spectra were often different from those obtained in solution
suggesting that the dyes were aggregated in the polymers.
Such aggregation avoids efficient poling, and investigationon the aggregation states of the dyes is important. In thisstudy, we grew single crystals of some CDCOP dyes withdifferent substituents and their crystallographic analyses
were conducted. Since molecular alignment in a crystal must
be a typical example for aggregation states of the molecule,crystal structure analyses of the dyes may be helpful toconsider the aggregation in the polymers. We also discussed
the relationship between the crystal structures and thecorresponding UV-visible diffuse reflectance spectra.

1．Introduction
For large-capacity information processing, ultrafast
switching devices are required, and one of the promising
candidates is electrooptic (EO) devices, in which opticalsignals are switched by applying electric field. Especially,organic compounds generally with low dielectric constants
are suitable for the EO materials. In addition, polymers
are advantageous in processability to fabricate opticalwaveguides including EO devices. Thus, development ofpractical EO polymers has been continued since 1980s1-3).
EO polymers are usually composed of matrix polymers andEO chromophores, which are dispersed in the polymers
or covalently bonded to the polymers. EO chromophores
should have large first hyperpolarizabilities (βs). Also theyshould have large dipole moments (μs) because the EO
effect only appears in noncentrosymmetric structures andEO chromophores in polymer matrices must be aligned inpolar orientation by applying DC electric field, i.e., poling.
However, large μ causes dipole-dipole interaction to form
antiparallel dimers and aggregates resulting in canceling outof dipole moments.
Recently, chromophores with a donor group and 4-cyano5-dicyanomethylene-2-oxo-3-pyrrolin-3-yl (CDCOP) groupas an acceptor have attracted attention as EO dyes4-7). SuchCDCOP derivatives have been reported over 50 years ago8,9).

2．Experimental
2.1 Synthesis of compounds
CDCOP derivatives were synthesized according to thescheme in Fig. 1. The detailed procedures are described
below.
1a: The mixture of 210) ( 4.0 g, 17.2 mmol) and N,Ndibutylaniline 3 (4.4 g, 20.0 mmol) in DMF (40 mL) was
stirred with cooling by an ice bath. To this, phosphorylchloride (4.8 mL, 52 mmol) was added dropwise, and stirring【Figures and illustrations】Figures and illustrations published in black andwhite in the journal can be seen in color at our public website「J-STAGE」.
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