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 crystals with the columnar packing structure exhibited linearly polarized emission, while the crystals with the cubic system did not show noticeable dichroism in either 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.

We have developed a novel triphenylmethane-based hexanuclear zinc complex that exhibits peculiar photochemical and photophysical properties. Upon UV irradiation, the compound turned from colorless to reddish purple, while the color of emission turned from blue to red. The color change was attributed to an oxidation of the ligand part. It was suggested that an intramolecular energy-transfer mechanism operates to give rise to the red emission. The UV treatment of a single crystal results in simultaneous emission of orthogonally polarized blue and red light. This color switching, namely linear dichroic emission was so distinct that one can recognize with by sight through optical microscope. The columnar arrangement of molecules in the crystal clearly accounts for the observed polarization of the emission.