Electrochemical Properties of Organic Dyes

The electrochemical properties of the 0.1 mM ZnTPyP molecule, rhodamine B, MO, and eosin B dichloromethane solution were measured with cyclic voltammetry (CV) using the conventional three-electrode system, in which a 3.0 mm diameter glass carbon disk (0.071 cm², Shanghai Chenhua) was used as the working electrode, a platinum wire was used as the counter electrode, and Ag/AgCl (silver/silver chloride) was used as the reference electrode (3.0 M KCl solution. The electrode potential was +0.22 V vs. the NHE potential, and 0.1 M of tetra-n-butylammonium hexafluorophosphate (TBAPF₆) was used as the electrolyte. The oxidation-reduction potential was measured through an electrochemical workstation. Based on the optical and electrochemical data, the energy levels of the HOMOs and LUMOs of the organic dyes can be estimated using Equations (2)–(4).
$${\mathrm{E}}_{\mathrm{g}}=\frac{\mathrm{hc}}{{\mathsf{\lambda }}_{\mathrm{abs}}}=\frac{1240}{{\mathsf{\lambda }}_{\mathrm{abs}}}$$
$${\mathrm{E}}_{\mathrm{HOMO}}=-{\mathrm{E}}_{\mathrm{ox}\left(\mathrm{vs}.\mathrm{Ag}/\mathrm{AgCl}\right)}-{\mathrm{E}}_{\mathrm{NHE}\left(\mathrm{vs}.\mathrm{Ag}/\mathrm{AgCl}\right)}-4.5$$
$${\mathrm{E}}_{\mathrm{LUMO}}={\mathrm{E}}_{\mathrm{HOMO}}-{\mathrm{E}}_{\mathrm{g}}$$
where E_g is the energy gap and λ_abs is the maximum UV–Vis absorption wavelengths value in the dichloromethane solution. E_HOMO and E_LUMO are the energy levels of the HOMOs and LUMOs, respectively. The standard hydrogen electrode (NHE) potential was −4.5 eV relative to the vacuum level. The CV curve test ranged from −1.6 V to 1.6 V, and the scan rate was 200 mV/s. All electrochemical tests were performed at 25 °C under N₂ saturation.