Functionalized porphyrin derivatives for solar energy conversion

Photocatalytic redox reactions with metalloporphyrins

Metalloporphyrinoids are utilized as efficient sensitizers and catalysts in photosynthesis and the reverse reaction that is respiration. Because metalloporphyrinoids show strong absorption in the visible region and redox active, metalloporphyrinoids are also suited as photoredox catalysts for photo-driven redox reactions using solar energy. In particular, metalloporphyrins are utilized as pivotal components to mimic the structure and function of the photosynthetic reaction center. Metalloporphyrins are used as photoredox catalysts for hydrogen evolution from electron and proton sources combining hydrogen evolution catalysts. Metalloporphyrins also act as thermal redox catalysts for photocatalytic reduction of CO2 with photoredox catalysts. Metalloporphyrins are also used as dual catalysts for a photoredox catalyst for oxygenation of substrates with H2O and a redox catalyst for O2 reduction when dioxygen is used as a two-electron oxidant and H2O as an oxygen source, both of which are the greenest reactants. Free base porphyrins can also be employed as promising photoredox catalysts for C–C bond formation reactions.

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

Maleimide-containing fluorinated porphyrins and chlorins were prepared based on the reaction of Zn(II) or Ni(II) complexes of 5,10,15,20-tetrakis(4-amino-2,3,5,6-tetrafluorophenyl)porphyrin and chlorin with maleic anhydride. Porphyrin maleimide derivatives were also prepared by the reaction of 5,10,15,20-tetrakis(4-azido-2,3,5,6-tetrafluorophenyl)porphyrinato Zn(II) or Ni(II) with N-propargylmaleimide via the CuAAC click reaction to afford fluorinated porphyrin-triazole-maleimide conjugates. New maleimide derivatives were isolated in reasonable yields and identified by UV-vis, 1H NMR, 19F NMR spectroscopy and mass-spectrometry.

The influence of antenna and anchoring moieties on the improvement of photoelectronic properties in Zn(ii)-porphyrin-TiO2 as potential dye-sensitized solar cells

A systematic study for the rational design of porphyrins (P4 spider-shaped derivatives) with potential application in dye-sensitized solar cells is presented. Using density functional theory (DFT) (B3LYP/6-31G*) and time-dependent DFT (M06/6-31G*) we show that the UV-vis absorption properties of a spider-shaped Zn(ii) porphyrin, previously synthesized by Stangel et al., may be greatly improved by applying some push-pull strategies in meso positions. We found that the selected triphenylamine push group induces a remarkable improvement in the absorption bands of P4 spider-shaped derivatives. The pull effect reached through the π-electron-rich phenyl group and the benzodithiazole (BTD) group allowed the Q bands to be red-shifted up to 689 nm, much longer than the 593 nm reported experimentally for the original spider-shaped porphyrin. The adsorption results of the P4 spider-shaped derivatives onto a TiO2-anatase surface model [Ti16O34H4] through the carboxylic acid group showed that the adsorptions energies were favourable and very similar in all cases. Natural bond orbitals (NBO) indicated a two-center bond (BD) O(carboxyl)-Ti(TiO2) for the porphyrin with the highest adsorption energy (8.27 kcal mol-1), and donor acceptor interactions from LP O(carboxyl) to Ti(TiO2) for the other porphyrins. The natural transition orbitals (NTO) for P4-derivatives-TiO2 confirm the nature of the excited states associated with Q and Soret bands. Finally, the frontier molecular orbitals revealed charge-separated states between those occupied and unoccupied, indicating a favourable charge-transfer process between the dyes and the surface conduction bands. In conclusion, this work showed a systematic study based on the push-pull strategy that improves the performance of porphyrins with the purpose to be used in dye-sensitized solar cells.

Push-Pull Zinc Porphyrins as Light-Harvesters for Efficient Dye-Sensitized Solar Cells

Dye-sensitized solar cell (DSSC) has been attractive to scientific community due to its eco-friendliness, ease of fabrication, and vivid colorful property etc. Among various kinds of sensitizers, such as metal-free organic molecules, metal-complex, natural dyes etc., porphyrin is one of the most promising sensitizers for DSSC. The first application of porphyrin for sensitization of nanocrystaline TiO2 can be traced back to 1993 by using [tetrakis(4-carboxyphenyl) porphyrinato] zinc(II) with an overall conversion efficiency of 2.6%. After 10 years efforts, Officer and Grätzel improved this value to 7.1%. Later in 2009, by constructing porphyrin sensitizer with an arylamine as donor and a benzoic acid as acceptor, Diau and Yeh demonstrated that this donor-acceptor framwork porphyrins could attain remarkable photovoltaic performance. Now the highest efficiencies of DSSC are dominated by donor-acceptor porphyrins, reaching remarkable values around 13.0% with cobalt-based electrolytes. This achievement is largely contributed by the structural development of donor and acceptor groups within push-pull framwork. In this review, we summarized and discussed the developement of donor-acceptor porphyrin sensitizers and their applications in DSSC. A dicussion of the correlation between molecular structure and the spectral and photovoltaic properties is the major target of this review. Deeply dicussion of the substitution group, especially on porphyrin's meso-position were presented. Furthermore, the limitations of DSSC for commercialization, such as the long-term stability, sophisticated synthesis procedures for high efficiency dye etc., have also been discussed.

Improved Optical and Morphological Properties of Vinyl-Substituted Hybrid Silica Materials Incorporating a Zn-Metalloporphyrin

This work is focused on a novel class of hybrid materials exhibiting enhanced optical properties and high surface areas that combine the morphology offered by the vinyl substituted silica host, and the excellent absorption and emission properties of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin-Zn(II) tetrachloride as a water soluble guest molecule. In order to optimize the synthesis procedure and the performance of the immobilized porphyrin, silica precursor mixtures of different compositions were used. To achieve the requirements regarding the hydrophobicity and the porous structure of the gels for the successful incorporation of porphyrin, the content of vinyltriacetoxysilane was systematically changed and thoroughly investigated. Substitution of the silica gels with organic groups is a viable way to provide new properties to the support. An exhaustive characterization of the synthesized silica samples was realised by complementary physicochemical methods, such as infrared spectroscopy (FT-IR), absorption spectroscopy (UV-Vis) and photoluminescence, nuclear magnetic resonance spectroscopy (²⁹Si-MAS-NMR) transmission and scanning electron microscopy (TEM and SEM), nitrogen absorption (BET), contact angle (CA), small angle X ray and neutron scattering (SAXS and SANS). All hybrids showed an increase in emission intensity in the wide region from 575 to 725 nm (Q bands) in comparison with bare porphyrin. By simply tuning the vinyltriacetoxysilane content, the hydrophilic/hydrophobic profile of the hybrid materials was changed, while maintaining a high surface area. Good control of hydrophobicity is important to enhance properties such as dispersion, stability behaviour, and resistance to water, in order to achieve highly dispersible systems in water for biomedical applications.

Increasing the lifetimes of charge separated states in porphyrin-fullerene polyads

Two linear polyads were designed using zinc(ii)porphyrin, [ZnP], and N-methyl-2-phenyl-3,4-fullero-pyrrolidine (C₆₀) where C₆₀ is dangling either at the terminal position of [ZnP]-C₆H₄-[triple bond, length as m-dash]-C₆H₄-[ZnP]-C₆₀ (1) or at the central position of [ZnP]-C₆H₄-[triple bond, length as m-dash]-C₆H₄-[ZnP(C₆₀)]-C₆H₄-[triple bond, length as m-dash]-C₆H₄-[ZnP] (2) in order to test whether the fact of having one or two side electron donors influences the rate of electron transfer, k_et. These polyads were studied using cyclic voltammograms, DFT computations, steady state and time-resolved fluorescence spectroscopy, and femtosecond transient absorption spectroscopy (fs-TAS). Photo-induced electron transfer confirmed by the detection of the charge separated state [ZnP˙+]/C₆₀˙^- from fs-TAS occurs with rates (k_et) of 3-4 × 10¹⁰ s^-1 whereas the charge recombinations (CRs) are found to produce the [ZnP] ground state via two pathways (central [ZnP˙+]/C₆₀˙^- (ps) and terminal central [ZnP˙+]/C₆₀˙^- (ns) producing [1ZnP] (ground state) and [3ZnP*]). The formation of the T₁ species is more predominant for 2.

Synthesis and characterization of zinc carboxy–porphyrin complexes for dye sensitized solar cells

DOTA-like porphyrin Zn complexes 8 afford new perspectives in DSSCs compared to mono-porphyrin counterpart 2, by displaying a PCE (%) of 7.13.

Programmable arrangement of metal ions in a cofacially stacked assembly of porphyrinoids toward molecular tags

Cofacial assemblies of metalloporphyrinoides represent a fascinating platform for the novel functional metal arrays to be molecular tags.

trans-A2B-corrole bearing 2,3-di(2-pyridyl)quinoxaline (DPQ)/phenothiazine moieties: synthesis, characterization, electrochemistry and photophysics

Singlet–singlet energy transfer and electron transfer processes in corrole–phenothiazine and corrole–DPQ dyads were demonstrated by using electrochemical and fluorescence (steady-state and time-resolved) spectral studies.

Arginine-induced porphyrin-based self-assembled nanostructures for photocatalytic applications under simulated sunlight irradiation

In this communication, we have investigated the arginine-induced fabrication of porphyrin (TCPP)-based supramolecular nanostructures. These self-assembled porphyrin nanostructures such as nanobelts show enhanced photocatalytic activity for the photodegradation of pollutant Rhodamine B under simulated visible-light irradiation.

Porphyrin-Based Dye-Sensitized Solar Cells (DSSCs): a Review

The current review aims to collect short information about photovoltaic performance and structure of porphyrin-based sensitizers used in dye-sensitized solar cells (DSSC). Sensitizer is the key component of the DSSC device. Structure of sensitizer is important to achieve high photovoltaic performance. Porphyrin derivatives are suitable for DSSC applications due to their thermal, electronic and photovoltaic properties. It describes some electrochemical and spectral properties as well as thestructure of porphyrin dyes used in dye based-solar cells.

Photosensitized H2 generation from "one-pot" and "two-pot" assemblies of a zinc-porphyrin/platinum nanoparticle/protein scaffold

We report photosensitized H2 generation using a protein scaffold that nucleates formation of platinum nanoparticles (Pt NPs) and contains "built-in" photosensitizers. The photosensitizers, zinc-protoporphyrin IX or zinc-mesoporphyrin IX (ZnP) were incorporated in place of the naturally occurring heme in the 24-subunit iron storage protein bacterioferritin (Bfr) when the ZnPs were added to the E. coli expression medium. We engineered a stable dimeric Bfr variant with two protein subunits sandwiching a ZnP. Ten glycines were also substituted in place of residues surrounding the vinyl side of the porphyrin in order increase access of solvent and/or redox agents. An optimized "one-pot" reaction of this glycine-substituted ZnMP-Bfr dimer with a Pt(iv) salt and borohydride resulted in a ∼50 : 50 mixture of protein in the form of Pt-free glycine-substituted ZnP-Bfr dimers and re-assembled 24-mers surrounding Pt NPs formed in situ. H2 production occurred upon visible light irradiation of this "one-pot" product when combined with triethanolamine as sacrificial electron donor and methyl viologen as electron relay. An analogous "two-pot" system containing mixtures of separately prepared Pt-free glycine-substituted ZnP-Bfr dimer and porphyrin-free Pt NP@Bfr 24-mer also showed robust photosensitized H2 generation. The glycine-substituted-ZnP-Bfr dimer thus served as photosensitizer for catalytic reduction of methyl viologen by triethanolamine, and the reduced methyl viologen was able to transfer electrons across the Bfr 24-mer protein shell to generate H2 at the enclosed Pt NP in a "dark" reaction. Our results demonstrate that Bfr is a readily manipulatable and versatile scaffold for photosensitized redox chemistry.

Photocurrent in Multilayered Assemblies of Porphyrin-Fullerene Covalent Dyads: Evidence for Channels for Charge Transport

Specially designed porphyrin-fullerene dyads have been synthesized to verify literature predictions based on quantum chemistry calculations that certain porphyrin-fullerene dyads are able to self-arrange into specific structures providing channels for charge transport in a bulk mass of organic compound. According to AFM and SEM data, the newly synthesized compounds were indeed prone to some kind of self-arrangement, although to a lesser degree than was expected. A dispersion corrected DFT study of the molecular non-covalent interactions performed at the DFT-D3 (B3LYP, 6-31G*) level of theory showed that the least energy corresponded to head-to-head dimers, with close contacts of porphyrin-porphyrin and fullerene-fullerene fragments, thus providing a unit building block of the channel for charge transport. Experimental proof for the existence of channels for charge transport was obtained by observing a photocurrent in a simple photovoltaic cell.

Pyridyl vs. bipyridyl anchoring groups of porphyrin sensitizers for dye sensitized solar cells

Two D–π–A porphyrins (A = pyridyl, bipyridyl) are synthesized and used as sensitizers in DSSCs. The enhanced photovoltaic performance of the bipyridyl-sensitized device is attributed to its faster electron injection and reduced charge recombination.

Two new bulky substituted Zn porphyrins bearing carboxylate anchoring groups as promising dyes for DSSCs

Two novel zinc-metallated porphyrins, bearing three and six long alkoxy chains at the periphery, have been synthesized as sensitizers in DSSCs.

Artificial hemes for DSSC and/or BHJ applications

In this review paper a summary of our studies is presented concerning the power conversion efficiency of DSSC and BHJ based on porphyrin hybrid materials.

Comparison of rhenium-porphyrin dyads for CO2 photoreduction: photocatalytic studies and charge separation dynamics studied by time-resolved IR spectroscopy

We report a study of the photocatalytic reduction of CO₂ to CO by zinc porphyrins covalently linked to [Re^I(2,2'-bipyridine)(CO)₃L]^+/0 moieties with visible light of wavelength >520 nm. Dyad 1 contains an amide C₆H₄NHC(O) link from porphyrin to bipyridine (Bpy), Dyad 2 contains an additional methoxybenzamide within the bridge C₆H₄NHC(O)C₆H₃(OMe)NHC(O), while Dyad 3 has a saturated bridge C₆H₄NHC(O)CH₂; each dyad is studied with either L = Br or 3-picoline. The syntheses, spectroscopic characterisation and cyclic voltammetry of Dyad 3 Br and [Dyad 3 pic]OTf are described. The photocatalytic performance of [Dyad 3 pic]OTf in DMF/triethanolamine (5 : 1) is approximately an order of magnitude better than [Dyad 1 pic]PF₆ or [Dyad 2 pic]OTf in turnover frequency and turnover number, reaching a turnover number of 360. The performance of the dyads with Re-Br units is very similar to that of the dyads with [Re-pic]⁺ units in spite of the adverse free energy of electron transfer. The dyads undergo reactions during photocatalysis: hydrogenation of the porphyrin to form chlorin and isobacteriochlorin units is detected by visible absorption spectroscopy, while IR spectroscopy reveals replacement of the axial ligand by a triethanolaminato group and insertion of CO₂ into the latter to form a carbonate. Time-resolved IR spectra of [Dyad 2 pic]OTf and [Dyad 3 pic]OTf (560 nm excitation in CH₂Cl₂) demonstrated electron transfer from porphyrin to Re(Bpy) units resulting in a shift of ν(CO) bands to low wavenumbers. The rise time of the charge-separated species for [Dyad 3 pic]OTf is longest at 8 (±1) ps and its lifetime is also the longest at 320 (±15) ps. The TRIR spectra of Dyad 1 Br and Dyad 2 Br are quite different showing a mixture of ³MLCT, IL and charge-separated excited states. In the case of Dyad 3 Br, the charge-separated state is absent altogether. The TRIR spectra emphasize the very different excited states of the bromide complexes and the picoline complexes. Thus, the similarity of the photocatalytic data for bromide and picoline dyads suggests that they share common intermediates. Most likely, these involve hydrogenation of the porphyrin and substitution of the axial ligand at rhenium.

Click made porphyrin–corrole dyad: a system for photo-induced charge separation

The preparation of the first porphyrin–corrole dyad through click chemistry is described.

New solution processed bulk-heterojunction organic solar cells based on a triazine-bridged porphyrin dyad as electron donor

An unsymmetrical porphyrin dyad (ZnP)-[triazine-Npip]-(ZnPCOOH) consisting of two zinc-porphyrin units covalently linked to a peridine-containing triazine group has been used with PC₇₁BM as electron donor and acceptor, respectively, for the active layer of solution-processed BHJ organic solar cells.