Two excited state proton transfer mechanisms of 3-hydroxyisoquinoline (3HIQ) in cyclohexane and acetic acid (ACID) were investigated based on the time-dependent density functional theory (TDDFT), suggesting a different double-proton transfer mechanism from the one proposed previously (J. Phys. Chem. B, 1998, 102, 1053). Instead of the formation of keto–enol complexes for 3HIQ self-association in cyclohexane, our theoretical results predicted that 3HIQ self-association exists in two forms: the normal form (enol/enol) and the tautomer form (keto/keto) in cyclohexane. A high barrier (37.023 kcal mol⁻¹) between the 3HIQ enol monomer and 3HIQ keto monomer form indicated that the 3HIQ keto monomer in the ground state should not exist. In addition, the constructed potential energy surfaces of the ground state and excited state have been used to explain the proton transfer process. Upon optical excitation, the enol/enol form is excited to the first excited state, then transfers one proton, in turn, transition to the ground state to transfer another proton. A relatively low barrier (8.98 kcal mol⁻¹) demonstrates two stable structures in the ground state. In view of the acetic acid solvent effect, two protons of 3HIQ/ACID transfer along the dihydrogen bonds in the first excited state, which is a different transfer mechanism to 3HIQ self-association. In addition, the proton transfer process provides a possible explanation for the fluorescence quenching observed.

We investigated the photoelectric properties of two indoline dyes (CA2 and CA3) with different conjugated length spacers, and the same cyanoacrylic acid acceptor, and global evaluation models were developed based on the experimental results, the developed normal model, the transient spectrum results, and the theoretical normal model. First, the properties of two dyes were studied through ultraviolet-visible spectroscopy, energy levels, and molecular descriptors. The observations agreed well with calculations carried out through basis-set correction. Second, the short-circuit current density (J_sc) and open-circuit voltage (V_oc) curve were estimated by using the developed normal model (DNM) based on the transient spectrum, molar extinction coefficient, adsorption capacity, and recombination rate. The values of the DNM method (J_sc = 16.24 mA cm⁻², V_oc = 0.59 V, η% = 7.81 for CA2) were closer to the experimental results (J_sc = 17.27 mA cm⁻², V_oc = 0.59 V, η% = 6.57) compared with the normal model (J_sc = 21.66 mA cm⁻², V_oc = 0.50 V and η% = 8.67), which was evaluated by using the electron-injection lifetime, excited-state lifetime, fluorescence lifetime, energy difference between the TiO₂ conduction band (E_CBE), and the electron difference between the donor and the recipient (n_c) for J_sc and V_oc. The DNM could be used to evaluate J_sc, V_oc, and η from considerations of the relationship between the macroscopic properties and microscopic parameters, and provided an effective method to improve the molecular design and performance tuning by decreasing factors that affect the energy conversion unfavorably.

The photoelectrical properties of two dyes—ethyl red and carminic acid—as sensitizers of dye-sensitized solar cells were investigated in experiments herein described. In order to reveal the reason for the difference between the photoelectrical properties of the two dyes, the ground state and excited state properties of the dyes before and after adsorbed on TiO₂ were calculated via density functional theory (DFT) and time-dependent DFT (TDDFT). The key parameters including the light harvesting efficiency (LHE), the driving force of electron injection ( $\Delta G^{\mathrm{inject}}$ ) and dye regeneration ( $\Delta G^{\mathrm{regen}}$ ), the total dipole moment ( ${\mathsf{\mu }}_{\mathrm{normal}}$ ), the conduction band of edge of the semiconductor ( $\Delta E_{\mathrm{CB}}$ ), and the excited state lifetime (τ) were investigated, which are closely related to the short-circuit current density ( $J_{\mathrm{sc}}$ ) and open circuit voltage ( $V_{\mathrm{oc}}$ ). It was found that the experimental carminic acid has a larger $J_{\mathrm{sc}}$ and $V_{\mathrm{oc}}$ , which are interpreted by a larger amount of dye adsorbed on a TiO₂ photoanode and a larger $\Delta G^{\mathrm{regen}}$ , excited state lifetime (τ), ${\mathsf{\mu }}_{\mathrm{normal}}$ , and $\Delta E_{\mathrm{CB}}$ . At the same time, chemical reactivity parameters illustrate that the lower chemical hardness (h) and higher electron accepting power (ω⁺) of carminic acid have an influence on the short-circuit current density. Therefore, carminic acid shows excellent photoelectric conversion efficiency in comparison with ethyl red.

Heavy metals have been widely applied in industry, agriculture, and other fields because of their outstanding physics and chemistry properties. However, heavy metal pollution is inevitable in the process of mass production and emission. Heavy metal ions will cause irreversible harm to the human body and other organisms due to their nondegradable nature even at low concentrations of exposure and ingestion. Therefore, it is of great significance for human health and ecological environment to develop high accuracy and sensitivity as well as stable techniques for detecting heavy metal ions. In recent years, surface‐enhanced Raman scattering (SERS) spectroscopy has been regarded as a promising new technique for the determination of trace heavy metal ions on account of its special fingerprint identification capability, high sensitivity, rapid detection ability, and simple operation. This review summarized in detail the basic principles and strategies for detecting mercury ions, copper ions, arsenic ions, zinc ions, cadmium ions, lead ions, and chromium (VI) ions as well as the current challenges and future trends for the determination of heavy metal ions based on SERS technology.