Tetraaryl ZnII Porphyrinates Substituted at β‐Pyrrolic Positions as Sensitizers in Dye‐Sensitized Solar Cells: A Comparison with meso‐Disubstituted Push–Pull ZnII Porphyrinates |
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Authors: | Dr Gabriele Di?Carlo Dr Alessio Orbelli?Biroli Prof Maddalena Pizzotti Dr Francesca Tessore Dr Vanira Trifiletti Dr Riccardo Ruffo Prof Alessandro Abbotto Dr Anna Amat Dr Filippo De?Angelis Prof Patrizia R Mussini |
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Institution: | 1. Dipartimento di Chimica dell'Università degli Studi di Milano, Unità di Ricerca dell'INSTM, Via C. Golgi 19, 20133 Milano (Italy), Fax: (+39)?02‐503‐14405;2. Istituto di Scienze e Tecnologie Molecolari del CNR (CNR‐ISTM), Via C. Golgi 19, 20133 Milano (Italy);3. Department of Materials Science, Solar Energy Research Center MIB‐SOLAR and INSTM Research Unit, University of Milano Bicocca, Via Cozzi 53, 20125 Milano (Italy);4. Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto di Scienze e Tecnologie Molecolari del CNR (CNR‐ISTM), Via Elce di Sotto 8, 06123 Perugia (Italy) |
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Abstract: | A facile and fast approach, based on microwave‐enhanced Sonogashira coupling, has been employed to obtain in good yields both mono‐ and, for the first time, disubstituted push–pull ZnII porphyrinates bearing a variety of ethynylphenyl moieties at the β‐pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β‐mono‐ or disubstituted ZnII porphyrinates and meso‐disubstituted push–pull ZnII porphyrinates. We have obtained evidence that, although the HOMO–LUMO energy gap of the meso‐substituted push–pull dyes is lower, so that charge transfer along the push–pull system therein is easier, the β‐mono‐ or disubstituted push–pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β‐monosubstituted porphyrinic dye interacting with a TiO2 surface and by the positive effect of the β substitution on the incident photon‐to‐current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350–650 nm). In contrast, meso‐substitution produces IPCE spectra with two less intense and well‐separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge‐transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β‐monosubstituted ZnII porphyrinates extremely promising sensitizers for use in DSSCs. |
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Keywords: | cyclic voltammetry density functional calculations porphyrins push– pull systems solar cells |
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