Enhanced Donor-π-Acceptor Character of a Porphyrin Dye Incorporating Naphthobisthiadiazole for Efficient Near-Infrared Light Absorption

Umbrella-Shaped m-Terphenyls for Highly π-Extended Planar Dyes toward High-Performance Dye-Sensitized Solar Cells

Porphyrin dyes with π-extended structures, particularly those with aromatic fused designs, have garnered considerable attention as efficient sensitizers for dye-sensitized solar cells (DCCSs). However, their photovoltaic performance has often been limited due to high aggregation tendencies caused by strong π-π interactions and charge recombination processes. Since m-terphenyls can be used as effective sterically protecting groups, the incorporation of umbrella-shaped m-terphenyls on the top of porphyrin dyes could provide an effective approach to unlock the full potential of highly π-extended porphyrin dyes. In this study, we report new fused porphyrin dyes, T-Ph, T-tBuPh, TT-Ph, and TT-tBuPh, introducing m-terphenyl groups. This innovative design ensures both blocking effects on dye aggregation on TiO2 and charge recombination against redox shuttles. Under the optimized conditions, DSSCs using thiophene-fused porphyrins T-Ph and T-tBuPh achieved a remarkable power conversion efficiency (PCE) of 11.5%. This is high compared to those with reference porphyrins, GY50 possessing steric hindrance due to the orthogonal orientation of a V-shaped diarylamino group to the porphyrin plane and DfZnP without the bulky umbrella-shaped m-terphenyl, demonstrating the proof of our concept. More importantly, the cosensitized DSSC using T-tBuPh and the complementary dye XY1B afforded the highest PCE of 12.3% ever reported for DSSCs with fused porphyrin dyes. This demonstrates that the "umbrella-shaped m-terphenyl" design is an attractive methodology for enhancing the photovoltaic performance of DSSCs with highly π-extended planar dyes, especially fused porphyrin dyes.

Synergistic meso-β regulation of porphyrins: squeezing the band gap into the near-infrared I/II region

The development of novel near-infrared (NIR) materials with extremely small energy gaps and high stability is highly desirable in bioimaging and phototherapy. Here we report an effective strategy for narrowing the energy gaps of porphyrins by synergistic regulation of meso/β substituents. The novel NIR absorbing/emitting meso-alkynyl naphthoporphyrins (Zn-TNP and Pt-TNP) are synthesized via the retro-Diels-Alder reaction. X-ray crystallography analysis confirms the highly distorted structures of the complexes. Both compounds exhibit intense Q bands around 800 nm, while Zn-TNP shows deep NIR fluorescence at 847 nm. Pt-TNP displays NIR-II room temperature phosphorescence peaking at 1106 nm with an extremely large Stokes shift of 314 nm, which are the longest wavelengths observed among the reported platinum porphyrinoids. Furthermore, Pt-TNP shows remarkable photostability and a notable capacity for synchronous singlet oxygen and heat generation under NIR light irradiation, demonstrating potential in combined photodynamic/photothermal therapy. A theoretical analysis reveals the progressive lifting of the HOMO by the β-fused benzene ring, the decrease of the LUMO upon meso-alkynyl substitution, and energy-releasing pathways varying with metal ions. This dual regulation approach demonstrates great promise in designing innovative multifunctional NIR porphyrin materials.

Ring Opening of Triflates Derived from Benzophospholan-3-one Oxides by Aryl Grignard Reagents as a Route to 2-Ethynylphenyl(diaryl)phosphine Oxides

A new simple method for the synthesis of 2-ethynylphenyl(diaryl)phosphine oxides via ring opening of benzophosphol-3-yl triflates has been developed. This process occurs via nucleophilic attack of a Grignard reagent at the phosphorus center, which results in ring opening and cleavage of a leaving group. The reaction proceeds under mild conditions and, within 15-60 min, leads to a library of previously unavailable 2-ethynylphenylphosphine oxides in yields up to 98%.

ThDione: A Powerful Electron-Withdrawing Moiety for Push-Pull Molecules

A series of new push-pull chromophores based on a combined cyclopenta[c]thiophene-4,6-dione (ThDione) acceptor, N,N-dimethylaniline, N-piperidinylthiophene or ferrocene donors, and ethylene or buta-1,3-dienylene π-linkers has been designed and synthesized. Utilizing one or two ThDione acceptors afforded linear or branched push-pull molecules. Experimental and theoretical study of their fundamental properties revealed thermal robustness up to 260 °C, a electrochemical/optical HOMO-LUMO gap that is tunable within the range of 1.47-2.19/1.99-2.39 eV, and thorough elucidation of structure-property relationships. Compared to currently available portfolio of heterocyclic electron-withdrawing units, ThDione proved to be a powerful and versatile acceptor unit. It imparts significant intramolecular charge transfer and polarizes the π-system, which results in enhanced (non)linear optical response.

D-π-A-Structured Porphyrins with Extended Auxiliary π-Spacers for Highly Efficient Dye-Sensitized Solar Cells

Zn(II)-porphyrin dyes (SGT-030 and SGT-031) with extended auxiliary π-spacers in the donor (D) part have been prepared and applied to dye-sensitized solar cells (DSSCs). The porphyrin dyes contained the same D-ethynyl-zinc porphyrinyl (ZnP)-ethynyl-benzothiadiazole-acceptor platform, but their donor groups varied from phenylene (Ph) in SGT-053 as a reference dye to the thieno[3,2-b]benzothiophene (TBT) and 4-hexyl-4H-thieno[3,2-b]indole (TI) moieties in SGT-030 and SGT-031, respectively. The effects of the extended auxiliary π-spacer in the D-π-A-structured porphyrin sensitizers on the molecular and photovoltaic properties were investigated via photophysical and electrochemical experiments as well as theoretical calculations. With the trend in conjugation length (Ph < TBT ≈ TI) and the donating ability of the π-spacer (Ph < TBT < TI), the absorption maxima and molecular absorptivity increased in the order SGT-053 (Ph) < SGT-030 (TBT) < SGT-031 (TI). The incorporation of TBT and TI promoted significant enhancements in the light-harvesting properties by reducing the energy gap and efficiently improving electronic communication. The DSSCs based on SGT-030 (10.80%) and SGT-031 (10.89%) with coadsorption of 4-(3,6-bis(4-((2-ethylhexyl)oxy)phenyl)-9H-carbazol-9-yl)benzoic acid in conjunction with the [Co(bpy)₃]^2+/3+-based electrolyte showed better power conversion efficiency than that of SGT-053 (9.10%). Electrochemical impedance spectroscopy analysis unveiled that the difference in J_sc and V_oc originates mainly from the twisted orientation between D and ZnP by the introduction of TBT and TI. This result indicated that the introduction of an extended auxiliary π-spacer in the donor part is a rational molecular design approach to improve photovoltaic performance by enhancing the light-harvesting ability and hindering charge recombination on the TiO₂ photoanode.

Multiply Wrapped Porphyrin Dyes with a Phenothiazine Donor: A High Efficiency of 11.7% Achieved through a Synergetic Coadsorption and Cosensitization Approach

Photocurrent ( J_sc) and photovoltage ( V_oc) are two important parameters for dye-sensitized solar cells (DSSCs) to achieve high power conversion efficiencies (PCEs). Herein, we synthesize four novel porphyrin dyes, XW36-XW39, using an N-phenyl-substituted phenothiazine donor to pursue higher PCE. For XW36 and XW37, the N-phenyl group is wrapped with two ortho-alkoxy chains. In contrast, it is substituted with a para-alkoxy group in XW38 and XW39. The phenothiazine wrapping in XW36 and XW37 induces more serious distortion, which is beneficial for anti-aggregation but unfavorable for the electron transfer from donor to a porphyrin framework. Thus, individual porphyrin dyes XW36 and XW37 exhibit efficiencies of 9.05 and 9.58%, respectively, lower than those of 9.51 and 10.0% achieved for XW38 and XW39, respectively. Besides, the introduction of a methyl group into a benzoic acid acceptor unit is conducive to anti-aggregation and thus improves the V_oc and efficiencies. Therefore, higher efficiencies were achieved for XW37 and XW39, compared with XW36 and XW38, respectively. Interestingly, although the individual XW36 dye shows a lowest efficiency among the four dyes, a highest efficiency of 11.7% was obtained for XW36 on the basis of synergetic adsorption with chenodeoxycholic acid and PT-C6 because of simultaneously improved J_sc and V_oc, which may be ascribed to the lowest dye-loading amount of XW36 among all of these porphyrin dyes, with the largest vacancy area left on the TiO₂ surface available for cosensitizer PT-C6, resulting in a highest J_sc. The high efficiency of 11.7% is one of the highest efficiencies using I^-/I₃^- electrolytes in DSSCs. These results provide an effective strategy for developing efficient DSSCs by the targeted coadsorption and cosensitization of porphyrin sensitizers optimized through introducing a bis( ortho-alkoxy)-wrapped phenyl group into the phenothiazine donor and/or methyl groups into the benzoic acid acceptor unit.