An Investigation on Gel-State Electrolytes for Solar Cells Sensitized with β-Substituted Porphyrinic Dyes

The presence of a liquid electrolyte in dye-sensitized solar cells (DSSCs) is known to limit the time stability of these devices due to leakage and evaporation phenomena. To overcome this issue, gel-state electrolytes may represent a good solution in order to maintain stability and good performances, albeit at lower costs. In the present work, two different kinds of gel-electrolytes, based on poly (methyl methacrylate) (PMMA) and nanoclay agents, were investigated in DSSC-devices sensitized using β-substituted Zn-porphyrins (namely ZnPC4 and ZnPC12) with enveloping alkoxy chains of different lengths, able to produce a coverage of the photoanode surface. The highest power conversion efficiency (PCE) values equal to 1.06 ± 0.04% and 1.55 ± 0.26% were obtained for ZnPC12 (with longer alkoxy chains) with PMMA- and nanoclay-based electrolytes respectively. The properties of the photoanode/electrolyte interface as well as the influence of the gelling agents on the final properties of the obtained devices were thoroughly characterized.

Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation

In the present work, sixteen different zinc porphyrins (possessing different meso substituents) with and without a chiral guest were modelled using DFT and TD-DFT approaches in order to understand the influence of various controlling factors on electronic circular dichroism (ECD) spectra. Two major aspects are influenced by these factors: excitation energy of the electronic transitions and their intensity. In the case of excitation energy, the influence increases in the following order: orientation of the peripheral substituents Collapse

Key Words

• circular dichroism
• density functional calculations
• porphyrins
• supramolecular chemistry
• transition metals

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MESH Headings Collapse

Grants

• PUTJD749 Estonian Research Council
• PRG399 Estonian Research Council
• 828779 European Union's H2020-FETOPEN
• Estonian Research Council

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Affiliation(s)

Irina Osadchuk Department of Chemistry and BiotechnologySchool of ScienceTallinn University of Technology AddressAkadeemia tee 1512618TallinnEstonia ICGMUniv MontpellierCNRS, ENSCMMontpellierFrance
Riina Aav Department of Chemistry and BiotechnologySchool of ScienceTallinn University of Technology AddressAkadeemia tee 1512618TallinnEstonia
Victor Borovkov Department of Chemistry and BiotechnologySchool of ScienceTallinn University of Technology AddressAkadeemia tee 1512618TallinnEstonia
Eric Clot ICGMUniv MontpellierCNRS, ENSCMMontpellierFrance

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On the excitation dependence of fluorescence spectra of meso-tetrapyridyl zinc (II) porphyrin and its relation with hydrogen bonding and outlying decoration

Zinc porphyrins are potential candidates for boosting the advancement of various technological applications, including those exploring the molecule's radiative emissions. In this work, the excitation dependence of fluorescence spectra from 5,10,15,20-meso-tetrapyridyl zinc(II) porphyrin dissolved in a binary solvent mixture of CHCl₃: MeOH, is reported. Important modifications in the profiles of the fluorescence bands are observed after exciting the molecules in a broad wavelength range from 350 to 565 nm. We attribute such modifications to the existence of two distinct relaxation pathways, related to two quasi-degenerated potential energy surfaces (PES) in the ZnTPyP's first excited state whose population rates changes for different excitation wavelengths. We also observed that by changing the CHCl₃:MeOH proportion in the binary mixture, a quenching mechanism mediated by the MeOH hydrogen bondings and ZnTPyP takes place, which allows for tuning the excitation dependence of the aforementioned relaxations pathways. Moreover, our data confirm that the addition of outlying RuCl(dppb)(bipy) ruthenium complex linked to the pyridyl moieties of the ZnTPyP ring is also an excellent strategy to modify the excitation dependence of the fluorescence relaxation pathways.

Diboron Porphyrins: The Raman Signature of the In-Plane Tetragonal Elongation of the Macrocycle

We describe an unusual in-plane type of porphyrin core distortion, tetragonal elongation (TE), observed experimentally in diboron porphyrins. The vibrational spectra of several of these complexes exhibit shifts that we have assigned to this TE distortion by comparing experimental spectra with DFT computational findings. The influence of TE in porphyrin systems was isolated using DFT analysis of the well-known model compounds Ni(II)porphine and Zn(II)porphine, with the macrocycle ring constrained to eliminate the influence of out-of-plane (OOP) distortions. A significant down-shift in frequencies was observed for porphyrin normal vibrational modes, particularly the in-plane A_1g/B_1g modes that are dominated by contributions from stretching and bending of C_α-C_m coordinates. In contrast, TE had little effect on the v(Pyr_halfring) and δ(Pyr_def) modes, though the lowered symmetry of the system resulted in significant splitting of the B_2u and B_3u modes. The impact of the TE distortion upon the diboron porphyrin vibrational spectrum was probed experimentally using Raman spectroscopy of B₂O₂(BCl₃)₂(TTP), B₂OF₂(TTP), and B₂OPhOH₂(TTP) (TTP = 5,10,15,20-(tetra- p-tolyl)porphyrin). Comparing the experimentally obtained spectral signatures to the computational findings allowed us to assign the large shifts observed for the v₂ and v₃ modes to the TE distortion in diboron porphyrins.

Computational and Spectroscopic Analysis of β-Indandione Modified Zinc Porphyrins

Porphyrins have characteristic optical properties which give them the potential to be used in a range of applications. In this study, a series of β-indandione modified zinc porphyrins, systematically changed in terms of linker length and substituent, resulted in absorption spectra that are dramatically different than that observed for the parent zinc porphyrin (ZnTXP, 5,10,15,20-tetrakis(3,5-dimethylphenyl)porphyrinato zinc(II)). These changes include strong absorptions at 420, 541, and 681 nm (110.2, 57.5, and 29.2 mM^-1 cm^-1, respectively) for the most perturbed compound. Computational studies were conducted and showed the different optical effects are due to a reorganization of molecular orbitals (MOs) away from Gouterman's four-orbital model. The substituent effects alter both unoccupied and occupied MOs. An increased length of linker group raised the energy of the HOMO-2 such that it plays a significant role in the observed transitions. The degenerate LUMO (e_g) set are split by substitution, and this splitting may be increased by use of a propylidenodinitrile group, which shows the lowest-energy transitions and the greatest spectral perturbation from the parent zinc porphyrin complex. These data are supported by resonance Raman spectroscopy studies which show distinct enhancement of phenyl modes for high-energy transitions and indandione modes for lower-energy transitions.

Modulation of Donor-Acceptor Distance in a Series of Carbazole Push-Pull Dyes; A Spectroscopic and Computational Study

A series of eight carbazole-cyanoacrylate based donor-acceptor dyes were studied. Within the series the influence of modifying the thiophene bridge, linking donor and acceptor and a change in the nature of the acceptor, from acid to ester, was explored. In this joint experimental and computational study we have used electronic absorbance and emission spectroscopies, Raman spectroscopy and computational modeling (density functional theory). From these studies it was found that extending the bridge length allowed the lowest energy transition to be systematically red shifted by 0.12 eV, allowing for limited tuning of the absorption of dyes using this structural motif. Using the aforementioned techniques we demonstrate that this transition is charge transfer in nature. Furthermore, the extent of charge transfer between donor and acceptor decreases with increasing bridge length and the bridge plays a smaller role in electronically mixing with the acceptor as it is extended.

Highly reducible π-extended copper corroles

Di- and octa-phenylethynyl (PE) substituted π-extended copper corroles were synthesized and characterized as to their structural, electrochemical and spectroscopic properties. The addition of two or eight PE groups to the β-pyrrole positions of the corrole results in dramatic red shifts in the electronic absorption spectra and new reductions which are not seen for the parent compound lacking PE substituents. CuCor(PE)₈ is reduced in four reversible one-electron transfer steps to give derivatives of [CuCor(PE)₈]^n- where n = 1, 2, 3 or 4. Variable temperature ¹H NMR and EPR measurements were carried out and suggest that the octa- and di-PE substituted Cu-corroles can both be described as an antiferromagnetically coupled Cu^II corrole cation radical which is in equilibrium with a triplet state, possibly due to a lower singlet-triplet energy gap as compared to 1 and 2 at room temperature. The EPR spectra of one-electron oxidized and one electron reduced species exhibited the characteristics of Cu(ii) corroles. The products generated in the first two reductions of each π-extended corrole were characterized by thin-layer spectroelectrochemistry, thus providing new insights into how UV-vis spectra of highly reduced corroles vary as a function of the number of PE groups and overall charge on the molecule. The singly reduced and singly oxidized copper corroles were also chemically generated in CH₃CN and shown to have UV-visible spectra almost identical to the spectra obtained by electroreduction or electrooxidation in PhCN or THF containing 0.1 M tetrabutylammonium perchlorate.

Highly electron deficient tetrabenzoquinone-appended Ni(ii) and Cu(ii) porphyrins: spectral, solvatochromatic, electrochemical redox and tuneable F−and CN−sensing properties

The electron deficient tetrabenzoquinone-appended porphyrins (1and2) were synthesized and utilized for the selective detection of CN⁻ions in aqueous media whereas they detect F⁻and CN⁻ions in nonaqueous media.

Predicting larger absorption cross-section in porphyrin dyes using DFT calculations

Porphyrin macrocycles play an important role in designing of fluorophores with superior light harvesting properties similar to that of antennas in biological systems. In this paper, new Zn(II)porphyrin dyes were investigated to improve the performance of the YD2-o-C8 using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Effects of various substituted and anchoring groups on basic porphine and Zn(II)porphyrin derivatives were systematically studied at the B3LYP/LanL2DZ level. The absorption spectra of Zn(II)porphyrin derivatives bearing one, two and four anchoring groups in the meso-positions were also studied. The calculations showed that a molecule [5, 10, 15, 20-(4-carboxyphenylethynyl)porphyrinato]Zn(II) have large absorption cross-section than available in the existing porphyrin dyes. The results of these calculations would open up enormous possibilities to develop porphyrin dyes characterized by high absorption cross-section for various light harvesting applications.

Influence of alkoxy chain envelopes on the interfacial photoinduced processes in tetraarylporphyrin-sensitized solar cells

We have investigated the effect of the alkoxy chain length and nature on the reduction of dye-to-dye aggregation as well as on the enhancement of light harvesting capabilities.

Synthesis, spectroscopic, electrochemical redox, solvatochromism and anion binding properties of β-tetra- and -octaphenylethynyl substituted meso-tetraphenylporphyrins

β-Phenylethynyl (PE) porphyrins exhibited unique photophysical properties and solvatochromic behavior due to ICT from the porphyrin core to PE moieties. Further, Zn(ii) porphyrins were utilized for anion sensing.

Porphyrin chemodosimeters: synthesis, electrochemical redox properties and selective ‘naked-eye’ detection of cyanide ions

β-Dicyanovinyl substituted porphyrins have been synthesized and utilized as chemodosimeters for ratiometric and colorimetric sensing of cyanide ions in CH₃CN and H₂O/CH₃CN mixture.

TDDFT study of the UV-vis spectra of subporphyrazines and subphthalocyanines

The UV-vis spectra of a series of subporphyrazines, SubPz(A,R), and subphthalocyanines, SubPc(A,R) ( A = F, Cl; R = H, F, CH3, C3H7, SCH3, SC2H5 and SPh), where A is the substituent attached to the central boron atom and R is the substituent attached to the periphery of the molecule have been analyzed through the use of TD–DFT calculations in vacuum and using chloroform as a solvent. The absorption spectra depend on both, the characteristics of the substituent attached to the periphery of the molecule and the extension of the π-system on going from SubPz to the SubPc analog. These latter effects lead to a red-shift of both the Q-band and the B-band, although the effect is larger for the former, mainly due to the increase of HOMO–LUMO energy gap on going from the SubPz to the SubPc analog. The effect of the substituents R is more intricate, because the profile of the absorption spectra changes depending on whether both substituents are on the same side (uu or dd) or on opposite sides (ud) of the molecular cone. Since the three conformers are rather close in energy, the observed spectra correspond, very likely, to the sum of the spectra of all of them.