Light Energy Collection in a Porphyrin–Imide–Corrole Ensemble

An assembly consisting of three units, that is, a meso‐substituted corrole ( C3 ), 1,8 naphthaleneimide ( NIE ), and a Zn porphyrin ( ZnP ), has been synthesized. NIE is connected to C3 through a 1,3‐phenylene bridge and to the ZnP unit through a direct C? C bond. The convergent synthetic strategy includes the preparation of a trans‐A₂B‐corrole possessing the imide unit, followed by Sonogashira coupling with a meso‐substituted A₃B‐porphyrin. The photophysical processes in the resulting triad ZnP-NIE-C3 are examined and compared with those of the corresponding C3-NIE dyad and the constituent reference models C3 , NIE , and ZnP . Excitation of the NIE unit in C3-NIE leads to a fast energy transfer of 98 % efficiency to C3 with a rate k_en=7.5×10¹⁰ s^?1, whereas excitation of the corrole unit leads to a reactivity of the excited state identical to that of the model C3 , with a deactivation rate to the ground state k=2.5×10⁸ s^?1. Energy transfer to C3 and to ZnP moieties follows excitation of NIE in the triad ZnP-NIE-C3 . The rates are k_en=7.5×10¹⁰ s^?1 and k_en=2.5×10¹⁰ s^?1 for the sensitization of the C3 and ZnP unit, respectively. The light energy transferred from NIE to Zn porphyrin unit is ultimately funneled to the corrole component, which is the final recipient of the excitation energy absorbed by the different components of the array. The latter process occurs with a rate k_en=3.4×10⁹ s^?1 and 89 % efficiency. Energy transfer processes take place in all cases by a Förster (dipole–dipole) mechanism. The theory predicts quite satisfactorily the rate for the ZnP/C3 couple, where components are separated by about 23 Å, but results in calculated rates that are one to two orders of magnitude higher for the couples NIE/ZnP (D/A) and NIE/C3, which are separated by distances of about 14 and 10 Å, respectively.     

The electronic structures and charge transfer properties of tetra(naphthalene‐dione)porphyrins and tetra(naphthalene‐dithione)porphyrins as dye‐sensitized solar cell skeleton

The p‐π conjugation of tetra(naphthalene‐dione)porphyrins and tetra(naphthalene‐dithione)porphyrins is clarified on the basis of density functional theory studies. When carbonyl/thionyl is introduced, π bonds on the molecular skeleton become strong–weak alternated, and the conjugation transforms from “benzene‐type” to “butadiene‐type.” The unidirectional photon‐induced current associated with the p‐π conjugation enables the light‐harvesting efficiency of this kind of molecular skeleton reaches 90% in the range of 300–800 nm. Therefore, these compounds are ideal alternative for panchromatic dye‐sensitized solar cells. © 2013 Wiley Periodicals, Inc.     

A p‐Quinodimethane‐Bridged Porphyrin Dimer

A p‐quinodimethane (p‐QDM)‐bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross‐conjugated keto‐linked porphyrin dimers 8 a and 8 b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel–Crafts alkylation of the diol‐linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one‐photon absorption (OPA, λ_max=955 nm, ε=45400 M ^?1 cm^?1) and a large two‐photon absorption (TPA) cross‐section (σ⁽²⁾_max=2080 GM at 1800 nm) in the near‐infrared (NIR) region due to its extended π‐conjugation and quinoidal character. It also exhibits a short singlet excited‐state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground‐state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto‐linked dimer 8 b . This research has revealed that incorporation of a p‐QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore.     

Molecular Engineering of Push–Pull Porphyrin Dyes for Highly Efficient Dye‐Sensitized Solar Cells: The Role of Benzene Spacers

Porphyrins have drawn much attention as sensitizers owing to the large absorption coefficients of their Soret and Q bands in the visible region. In a donor and acceptor zinc porphyrin we applied a new strategy of introducing 2,1,3‐benzothiadiazole (BTD) as a π‐conjugated linker between the anchoring group and the porphyrin chromophore to broaden the absorption spectra to fill the valley between the Soret and Q bands. With this novel approach, we observed 12.75 % power‐conversion efficiency under simulated one‐sun illumination (AM1.5G, 100 mW cm^?2). In this study, we showed the importance of introducing the phenyl group as a spacer between the BTD and the zinc porphyrin in achieving high power‐conversion efficiencies. Time‐resolved fluorescence, transient‐photocurrent‐decay, and transient‐photovoltage‐decay measurements were employed to determine the electron‐injection dynamics and the lifetime of the photogenerated charge carriers.     

Dramatic Influence of an Anionic Donor on the Oxygen‐Atom Transfer Reactivity of a MnV–Oxo Complex

Addition of an anionic donor to an Mn^V(O) porphyrinoid complex causes a dramatic increase in 2‐electron oxygen‐atom‐transfer (OAT) chemistry. The 6‐coordinate [Mn^V(O)(TBP₈Cz)(CN)]^? was generated from addition of Bu₄N⁺CN^? to the 5‐coordinate Mn^V(O) precursor. The cyanide‐ligated complex was characterized for the first time by Mn K‐edge X‐ray absorption spectroscopy (XAS) and gives Mn?O=1.53 Å, Mn?CN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN^? complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e^?‐reduced Mn^III(CN)^? complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000‐fold versus the same reaction for the parent 5‐coordinate complex. An Eyring analysis gives ΔH^≠=14 kcal mol^?1, ΔS^≠=?10 cal mol^?1 K^?1. Computational studies fully support the structures, spin states, and relative reactivity of the 5‐ and 6‐coordinate Mn^V(O) complexes.