Photooxidation and Photoluminescence of Triarylmethane Dye-Conjugated Zinc Complexes: Optical Anisotropy and Optical Activity Emerging from Distinct Crystal Packing Modes Saori Takeda, 1 Hiroka Yamada, 1 Shunpei Takezawa, 1,3 Isao Yoshikawa, 1 Hidetake Seino, 2 Kazunari Matsumura, 3 and Hirohiko Houjou* 1 1 Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 2 Faculty of Education and Human Studies, Akita University, 1-1 Tegata-Gakuenmachi, Akita 010-8502 3 Department of Materials Science and Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Tokyo 135-8548 E-mail: houjou@iis.u-tokyo.ac.jp Received: December 24, 2014; Accepted: February 4, 2015; Web Released: February 18, 2015 A series of hexanuclear zinc complexes was prepared using a triarylmethane (TAM)-based ligand. Depending on the alkyl chains at the peripheral position of the complex, the complexes crystallized as needles, octahedral crystals, or both. A needle crystal consisting of molecular columns in which P- and M-forms of propeller-shaped complexes were alternately stacked. Octahedral crystals had an enantiomeric cubic system. All crystals were photooxidized under UV irradiation to yield the corresponding TAM dyes with characteristic absorption (ca. 540 nm) and emission (ca. 600 nm) spectra. The crystalswith the columnar packing structure exhibited linearly polarized emission, while the crystalswith the cubic system did not show noticeabledichroism ineither absorption or emission. The differences in photophysical properties among the complexes with various alkanoic groups were interpreted in terms of the spatial arrangement of the TAM dye molecules in the crystals. Dichroic dyes are optically anisotropic materials that show photoabsorption, photoluminescence, or both with remarkable angular dependence of the polarization plane. These dyes are potentially applicable to a wide area including nonlinear op- tics, three-dimensional displays, and quantum computation. 1,2 Recent attempts to fabricate such materials have used the dispersion of nanoparticles or organic compounds into polymer films, 3,4 guest-host interactions in anisotropic media such as liquid crystals or clays, 5-13 and self-assembly induced by van der Waals and solvophobic interactions. 14-18 Organic crystalline materials are of particular interest when one can incorporate multiple emission modes with different transition moment vectors into a unit molecule. The crystal packing or aggregation pattern can play a decisive role in controlling solid-state luminescence, 19-22 which is enhanced or weakened depending on the mutual arrangement of the transition moment vectors of the chromophore. Ahighly axisymmetric moleculewith a rigid core can be a useful building unit that forces functional moieties to have a preferred arrangement in the solid state. 23-26 In this regard, tri- arylmethane (TAM) derivatives have been extensively stud- ied and applied in supramolecular complexes, 27-29 nanoscale fibers, 30 self-assembled monolayers, 31 and liquid crystals. 32 The leuco form of TAM is photooxidized under UV irradiation, releasing hydride, hydroxide, or cyanide from the central car- bon atom. 33-35 Thus, a virtuallyplanar methylium π-system exhibits the vivid colors of synthetic dyes such as crystal violet. 36-38 By virtue of this color-developing property, a variety of TAMs with different aryl groups, including hetero- aromaticrings, have been developed 39 and applied in a variety offunctional dyes, including nonlinear optical materials and near-infrared dyes. 40-46 We recently reported the crystal struc- ture as well as the photochemical and photophysical properties of a novel TAM derivative with μ-phenoxo-bridged dinuclear zinc complexes on each apex. 47 This C 3 -symmetric hexanuclear Zn complex crystallized as hexagonal rods and exhibited a UV- induced color change and blue/red bimodal emissions with orthogonal polarization planes. In a previous paper, 47 we focused on a TAM complex derivative with acetate ions attached to zinc ions. In the crystal structure, the methyl groups serve as peripheral decorations of the molecule and face the same group of neighboring mole- cules. Accordingly, replacing acetate with some other carbox- ylate should modulate the molecular packing and hence the photophysical properties of the crystal. In this paper, we describe the synthesis and crystal packing of several TAM complexes with various carboxylate chains on their periphery. We observed a marked difference in their photooxidation and photoluminescent behaviors, which could be explained by the packing structure. Results and Discussion Synthesis. The TAM-type ligand (1H 3 ) was prepared according to the reported procedure. 47 Addition of zinc nitrate to the ligand solution resulted in the hexanuclear complex Zn 6 1(NO 3 ) 9 (Scheme 1). The nitrate ions connected to the zinc ions were replaced with carboxylate ions, and the other nitrate ions were exchanged with hexafluorophosphate ions, resulting 698 | Bull. Chem. Soc. Jpn. 2015, 88, 698–705 | doi:10.1246/bcsj.20140403 © 2015 The Chemical Society of Japan