Surface Photovoltage, Luminescence, and Cyclic Voltammetry on the First Series of Lanthanide(III) Monobenzoporphyrin Compound Liquid Crystals and Relative Transition Metal Benzoporphyrin Compound Liquid Crystals

Abstract

The first series of lanthanide(III) monobenzoporphyrin liquid crystalline compounds, meso-tetraalkyltetrabenzoporphyrin (TATBP) ytterbium hydroxy, and relative transition metal benzoporphyrin liquid crystalline compounds (4 series, 24 kinds) are reported that display a hexagonal columnar discotic columnar (Colh, previously designated Dh) phase. These liquid crystalline compounds have been studied by cyclic voltammetry, luminescence, and surface photovoltage spectroscopies. In a dimethylformamide (DMF) solution of 0.1 M tetrabutylammonium perchlorate (TBAP), the synthesized TATBP and TATBPZn exhibit two one-electron reversible redox reactions, and TATBPYbOH and TATBPCoCl show three redox reactions, respectively, within the accessible potential window of the solvent and the measured electrochemical redox potentials. The absorption bands of the porphyrins appear in the ranges 425−438 (Soret band), 572−581 (Q-band), and 625−631 (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 compounds are P-type semiconductors. The spectral bands of TATBP and metal TATBP correspond to the π → π* transition, and the metal ion corresponds to the π* orbital (d → eg(π*)) transition, respectively. The electron (or hole) can be trapped on the liquid crystal porphyrin film by applying both light and a negative (or positive) electric field. Quantum yields of the S1 → S0 fluorescence are in the region 0.20−0.28, and the fluorescence lifetimes are in the region 0.015−0.028 ms at room temperature. The phosphorescence bands of the complexes at 77 K appear in the range 715−725 nm. It is found that the stronger the fluorescence intensity is, the weaker the surface photovoltage intensity is. The TATBPCo(III)Cl are 1:1 type electrolytes. The study contributes to further choice and applications of the liquid crystals.