Photooxidation and Photoluminescence of Triarylmethane Dye-Conjugated Zinc Complexes: Optical Anisotropy and Optical Activity Emerging from Distinct Crystal Packing Modes

Abstract

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.

Triarylmethane dye-conjugated hexanuclear zinc complexes: Photophysical properties and cyanide anion-binding behavior

“…2) exhibited a series of broadened doublet peaks corresponding to the diastereotopic methylene protons and some broadened peaks corresponding to the aromatic protons, suggesting suppressed intramolecular motion due to the rigidity and steric bulk of the molecular framework; such suppression of motion has also been observed for the corresponding leuco complex, 1c [22]. The absence of a methine proton in the spectrum of 2c evidences the formation of the dye form.…”

“…[Zn 6 1(OCOC 9 H 19 ) 6 ](PF 6 ) 3 (1b) was synthesized according to the reported procedure [22]. 1b (34 mg, 0.01 mmol) was dissolved in acetone (3 mL), to which a methanolic solution (2 mL) of potassium hexafluorophosphate (1.8 mg, 0.01 mmol), and a methanol solution (2 mL) of ceric ammonium nitrate (11 mg, 0.02 mmol) was successively added.…”

“…The solution was left for 24 h at ambient temperature, resulting in a turbid suspension. [Zn 6 L re (OCOCH(C 6 H 13 )C 8 H 17 ) 6 ] (PF 6 ) 3 (1c) was synthesized according to the reported procedure [22]. 1c (196 mg, 0.05 mmol) was dissolved in acetone (10 mL), to which an acetonic solution (10 mL) of potassium hexafluorophosphate (9 mg, 0.05 mmol), and an acetone solution (10 mL …”

“…Crystal structures were solved by direct methods (i.e., using SIR2011) [23] and refined by the full-matrix least-squares method (i.e., using SHELXL-2013) [24]. The crystal was racemic twin, and the twinning was resolved using the program TwinRotMat [25] 3 , where L re denotes the reduced form of the ligand; Scheme 1) were prepared by means of a previously reported procedure [22]. These complexes were converted to the corresponding colored species by the addition of ceric ammonium nitrate as an oxidation reagent and KPF 6 as an anion source for charge compensation.…”

“…Recently, we developed a series of hexanuclear zinc complexes conjugated with 4,4 0 ,4 00 -trihydroxytriphenylmethane, the leuco form of aurin, a representative TAM dye [21,22]. As prepared, the complexes are colorless and exhibit blue photoluminescence; prolonged UV irradiation of the complexes induces a color change and a bimodal emission profile (blue and red) with orthogonal polarization planes [21].…”