Photooxidation and photoluminescence of triarylmethane dye-conjugated zinc complexes: Optical anisotropy and optical activity emerging from distinct crystal packing modes

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.