Antimony(+5) insertion induces both electron-rich and electron-poor parts within the porphyrin structure resulting in a push–pull style intramolecular charge transfer.

Photodynamics of an aluminum(iii) porphyrin-phosphorous(v) porphyrin heterodimer reveals initial formation of a singlet CT state which relaxes to a high-energy triplet CT state lasting for about 105 μs.

A high-potential supramolecular triad (TPE-AlPor ← Im-C60) composed of aluminum­(III) porphyrin (AlPor), fullerene (C60), and tetraphenylethylene (TPE) has been constructed. The fullerene and tetraphenylethylene units are bound axially to opposite faces of the porphyrin plane via coordination and covalent bonds, respectively. The ground and excited-state properties of the triad and reference dyads are studied using steady-state and time-resolved spectroscopic techniques. The transient data show that photoexcitation results in charge separation from tetraphenylethylene to the excited singlet state of the porphyrin (1AlPor*), generating a high-energy (2.14 eV) charge-separated state, (TPE)•+-(AlPor)•–, in toluene. A subsequent electron migration from the AlPor–• to fullerene generates a second high-energy (1.78 eV) charge-separated state (TPE)•+-AlPor ← Im-(C60)•–. The lifetime of the charge separation is about 25 ns. The high energy stored in the form of charge-separated states along with their reasonable lifetimes makes these donor–acceptor systems potential electron-transporting catalysts to carry out energy-demanding photochemical reactions, especially in artificial photosynthesis for conversion of solar energy into chemical energy.

To study the photophysical and redox properties as a function of meso-aryl units, a series of hypervalent phosphorus­(V) porphyrins, PP­(OMe)2·PF6, PMP­(OMe)2·PF6, PDMP­(OMe)2·PF6, P345TMP­(OMe)2·PF6, and P246TMP­(OMe)2·PF6, with phenyl (P), 4-methoxyphenyl (MP), 3,5-dimethoxyphenyl (DMP), 3,4,5-trimethoxyphenyl (345TMP), and 2,4,6-trimethoxyphenyl (246TMP) units, respectively, have been synthesized. The P­(+5) in the cavity makes the porphyrin ring electron-poor, whereas the methoxy groups make the meso-phenyl rings electron-rich. The presence of electron-rich and electron-poor portions within the porphyrin molecule promoted an intramolecular charge transfer (ICT). Also, the study suggests that the ICT depends on the number and position of the methoxy groups. The ICT is more prominent in m-methoxy-substituted phosphorus­(V) porphyrins (PDMP­(OMe)2.PF6, P345TMP­(OMe)2·PF6) and almost no ICT was found in no-methoxy, o-methoxy, and/or p-methoxy phosphorus­(V) porphyrins (PP­(OMe)2·PF6, PMP­(OMe)2·PF6, P246TMP­(OMe)2·PF6). Transient absorption studies indicate that the ICT takes place on the picosecond time scale. The most striking results come from P246TMP­(OMe)2·PF6, where each phenyl ring carries three methoxy units, like the P345TMP­(OMe)2·PF6, but it failed to induce the ICT process. Electrochemical studies and time-dependent density functional theory (TD-DFT) calculations were used to support the experimental results. This study extensively explores why and how slight variations in meso-aryl substitutions lead to intricate changes in the photophysical and redox properties of phosphorus­(V) porphyrins.

Six new "axial-bonding" type "phosphorus(V) porphyrin−naphthalene" conjugates have been prepared consisting of oct a et hyl porp h yrina to pho s pho rus (V ) ( P OEP + )/ tetraphenylporphyrinatophosphorus(V) (PTPP + ) and naphthalene (NP). The distance between the porphyrin and NP was systematically varied using polyether bridges. The unique structural topology of the octaethylporphyrinatophosphorus(V) (POEP + ) and tetraphenylporphyrinatophosphorus(V) (PTPP + ) enabled construction of mono-and disubstituted phosphorus(V) porphyrin−naphthalene conjugates, respectively. The steady-state and transient spectral properties were investigated as a function of redox properties, distance, and molecular topology. Strong electronic interactions between the phosphorus(V) porphyrin and NP in directly bound conjugates were observed. The established energy diagrams predicted reductive electron transfer involving singlet excited phosphorus(V) porphyrin and NP to generate high-energy (∼1.83−2.11 eV) charge-separated states (POEP/ PTPP) • −(NP) •+ . Femtosecond transient absorption spectral studies revealed rapid deactivation of singlet excited phosphorus(V) porphyrin due to charge separation wherein the estimated forward rate constants were in the range of 10 9 −10 10 s −1 and were dependent on the distance between the NP and porphyrins units, as well as the redox potentials of the type of the phosphorus(V) porphyrin. Additionally, due to high exothermicity and low-lying triplet states, the charge recombination process was found to be rapid, leading to populating the triplet states of phosphorus(V) porphyrins.

A series of fluorinated free-base porphyrins (H2TPPF[Formula: see text], [Formula: see text] = 0, 8, 12, 20, 24) and the corresponding aluminum(III) porphyrin (AlTPPF[Formula: see text]-Ph, [Formula: see text] = 0, 8, 12, 20, 24) derivatives have been synthesized and their spectroscopic, redox and optical properties were investigated. The absorption studies show that the spectral shapes of investigated porphyrins are sensitive to the degree of fluorination on the meso-phenyl units. Analogously, the fluorescence quantum yields and singlet-state lifetimes depend on the number of fluorine atoms, and decrease by increasing the number of fluorine atoms. The H2TPPF[Formula: see text] and AlTPPF[Formula: see text]-Ph ([Formula: see text] = 8, 12, 20, 24) derivatives exhibited lower fluorescence intensities compared to the H2TPP and AlTPP, respectively. However, the AlTPPF[Formula: see text]-Ph ([Formula: see text] = 0, 8, 12, 20, 24) derivatives yield relatively a strong fluorescence compared to the well-known ZnTPP. As predicted, the redox potentials are shifted to the more positive side by increasing the fluorine atoms. The Lewis acidity of AlTPPF[Formula: see text]-Ph was quantified by using the absorption and fluorescence titrations with the Lewis base [Formula: see text]-methylimidazole (Me-Im). The titration data suggests that the Lewis acidity of the Al center rises when increasing the number of fluorine atoms on the porphyrin. Together, the high fluorescence quantum yields, high-potentials, unique optical and redox properties suggest that the investigated porphyrins could be potential sensitizers to mimic various components of artificial photosynthetic systems for the production of solar fuels.

Vertically assembled photoanodes, consisting of aluminum(iii) porphyrin, an electron donor, and semiconductor TiO2, have been fabricated and their photophysical properties investigated.

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