A porphyrinic metal–organic framework (PMOF) known as PCN-222­(Zn) was chemically doped with a molecular Re­(I) catalyst-bearing carboxylate anchoring group to form a new type of metal–organic framework (MOF)–Re­(I) hybrid photocatalyst. The porphyrinic MOF-sensitized hybrid (PMOF/Re) was prepared with an archetypical CO2 reduction catalyst, (L)­ReI(CO)3Cl (Re­(I); L = 4,4′-dicarboxylic-2,2′-bipyridine), in the presence of 3 vol % water produced CO with no leveling-off tendency for 59 h to give a turnover number of ≥1893 [1070 ± 80 μmol h–1 (g MOF)−1]. The high catalytic activity arises mainly from efficient exciton migration and funneling from photoexcited porphyrin linkers to the peripheral Re­(I) catalytic sites, which is in accordance with the observed fast exciton (energy) migration (≈1 ps) in highly ordered porphyrin photoreceptors and the effective funneling into Re­(I) catalytic centers in the Re­(I)-doped PMOF sample. Enhanced catalytic performance is convincingly supported by serial photophysical measurements including decisive Stern–Volmer interpretation.

Three phenothiazine-based A−π−D−π−D−π−A-type small molecules containing various terminal acceptor units, which act as Lewis base blocks, have been synthesized via an efficient and stepeconomical, direct C−H arylation strategy in the aim toward the development of hole-transporting materials (HTMs) with multifunctional features (such as efficient hole extraction layer, trap passivation layer, and hydrophobic protective layer) for perovskite solar cells (PrSCs). Optical-electrochemical correlation and density functional theory studies reveal that dicyanovinylene acceptor in SGT-421 downshifted the highest occupied molecular orbital (HOMO) level (−5.41 eV), which is more proximal to the valence band (−5.43 eV) of the perovskite, whereas N-methyl rhodanine in SGT-420 and 1,3indanedione (IND) in SGT-422 destabilized the HOMO, leading to an increased interfacial energy-level offset. SGT-421 exhibits superior properties in terms of a sufficiently low-lying HOMO level and favorable energy-level alignment, intrinsic hole mobility, interfacial hole transfer, hydrophobicity, and trap passivation ability over spiro-OMeTAD as a benchmark small-molecule HTM. As envisaged in the design concept, SGT-421-based PrSC not only yields a comparable efficiency of 17.3% to the state-of-art of spiro-OMeTAD (18%), but also demonstrates the enhanced long-term stability compared to the spiro-OMeTAD because of its multifunctional features. More importantly, the synthetic cost of SGT-421 is estimated to be 2.15 times lower than that of spiro-OMeTAD. The proposed design strategy and the study of acceptor−property relationship of HTMs would provide valuable insights into and guidelines for the development of new low-cost and efficient multifunctional HTMs toward the realization of efficient and long-term stable PrSCs.

The catalytic efficacy of photochemical CO2 reduction by the bipyridyl (bpy) half-metallocene Ir­(III) complex, [Cp*Ir­(bpy)­Cl]+, was evaluated in both homogeneous and heterogeneous manners. The catalyst and photosensitizer were modified in order to be commonly engaged in each system, [Cp*Ir­(4,4′-Y2-bpy)­Cl]+ (Cp*IrPE, Y = CH2PO­(OEt)2; Cp*IrP, Y = CH2PO­(OH)2) and [Ir­(C∧N)2(4,4′-Y2-bpy)]+ (IrPE, C∧N = 1-phenylisoquinoline, Y = CH2PO­(OEt)2; IrP, Y = CH2PO­(OH)2), respectively. This modification rendered the mixed homogeneous or heterogeneous ternary hybrid system, IrPE + Cp*IrPE or IrP/TiO2/Cp*IrP, respectively, from which the catalytic performance of the half-metallocene Ir­(III) was assessed. The mixed homogeneous system (IrPE + Cp*IrPE) produced formate as a major CO2 reduction product with a maximal turnover number (TON) of ∼800 for 48 h. In contrast, the heterogeneous ternary hybrid (IrP/TiO2/Cp*IrP) yielded both CO and formate with 16.7 vol % TEOA additive (TONCO/formate > 560 for 100 h), reflecting the idea that two different catalytic routes for CO2 reduction exist. The mechanistic investigations along with electrochemical and photophysical studies suggest that the homogeneous catalysis involves Cp*IrIII–H intermediate for formate production, while the heterogeneous catalysis undergoes multiple electron transfer pathways involving the energy lowering of the bipyridine ligand as it is anchored onto the electron-withdrawing n-type TiO2 support.