Synthesis and properties of transition metal benzoporphyrin compound liquid crystals

Abstract

meso-Tetraalkyltetrabenzoporphyrin (TATBP) and related transition metal benzoporphyrin liquid crystalline compounds, TATBPMnCl, TATBPNi, and TATBPCu (4 series, 28 kinds) are reported that display a hexagonal columnar discotic columnar (Col_h) phase. These liquid crystalline compounds have been studied by cyclic voltammetry, surface photovoltage spectroscopy (SPS), and luminescence spectroscopy. In dimethylformamide (DMF), 0.1 M tetrabutylammonium perchlorate (TBAP), these synthesized compounds exhibit two one-electron reversible redox reactions, within the accessible potential window of the solvent and the measured electrochemical redox potentials. The absorption bands of the complexes appear in the range 425–431 (Soret band), 576–579 (Q band) and 627–631 (Q band ) nm. The photovoltaic properties and charge transfer process of the liquid crystalline compounds were investigated by surface photovoltage spectroscopy (SPS) and electric-field-induced surface photovoltage spectroscopy (EFISPS) techniques, which reveal that all the compounds are p-type semiconductors. The spectral bands of TATBP and metal TATBP correspond to π → π* transitions. Electrons (or holes) can be trapped on the liquid crystal porphyrin film by applying both light and negative (or positive) electric field. Quantum yields of the S₁ → S₀ fluorescence are in the region 0.19–0.29 and the fluorescence lifetimes are in the region 0.015–0.017 ms at room temperature. The phosphorescence bands of the complexes at 77 K appear at 725 nm. It is found that the stronger the fluorescence intensity is, the weaker the surface photovoltage intensity is. The TATBPMn(III)Cl are 1 ∶ 1 type electrolytes. The study contributes to further choice and applications of the liquid crystals.