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Transparent and colorless solar cells are attractive new photovoltaic devices as they could bring new opportunities to harness sunlight energy and particularly for their integration in windows. In this work, a new zinc phthalocyanine was synthesized and investigated as sensitizer in dye-sensitized solar cell (DSSC) for this purpose. The zinc phthalocyanine features a benzoic acid anchoring group and six thio(4-tertbutylphenyl) substituents in ${\alpha }$ position of the phtalocyanine. The dye was characterized by absorption and emission spectroscopy and by electrochemistry. The physico-chemical properties show that the dye fulfills the criteria for such an application. A detailed computational study indicates that the electronic communication with $\mathrm{TiO}_{2}$ conduction is weak owing to the absence of overlapping of the wavefunctions of the dye with those of the $\mathrm{TiO}_{2}$ semiconductor. The photovoltaic performances of the zinc phthalocyanine were measured in $\mathrm{TiO}_{2}$-based DSSC that revealed inefficient electron injection, which certainly can be explained by the weak electronic coupling of the dye with $\mathrm{TiO}_{2}$ that limits electron injection efficiency. A strategy is proposed to make better-performing sensitizers.

Photophysical, photovoltaic, and charge transport properties of fused core-modified expanded porphyrins containing two pyrroles, one dithienothiophene (DTT) unit, and 1–4 thiophenes (1–4) were inspected by using density functional theory (DFT) and time-dependent DFT. Compounds 1–3 have been investigated experimentally before, but 4 is a theoretical proposal whose photophysical features match those extrapolated from 1 to 3. They exhibit absorption in the range of 700–970 nm for their Q bands and 500–645 nm for their Soret bands. The rise of thiophene rings placed in front of the DTT unit in the expanded porphyrin ring causes a bathochromic shift of the longest absorption wavelength, leading to near-infrared absorptions, which represent 49% of the solar energy. All the systems show a thermodynamically favorable process for the electron injection from the dye to TiO2 and adsorption on a finite TiO2 model. The electron regeneration of the dye is only thermodynamically feasible for the smallest expanded porphyrins 1 and 2 when I−/I3− electrolyte is used. The charge transport study shows that for voltages lower than 0.4 V, junctions featuring pentaphyrin 1 and octaphyrin 4 are more conductive than those containing hexaphyrin 2 or heptaphyrin 3. The results showed that the four fused core-modified expanded porphyrins investigated are potential dyes for applications in dye-sensitized solar cells, mainly pentaphyrin 1 and hexaphyrin 2. Moreover, increasing the number of thiophene rings in the macrocycle proved fruitful in favoring absorption in the near-infrared region, which is highly desired for dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) compounds offer a promising avenue for improving the performance of solar cells. Using TD-DFT methods, anti-Kasha azulene derivatives that could carry out SF have been designed. For this purpose, substituted azulenes with a donor (–OH) and/or an acceptor group (–CN) have been systematically studied using the S2 ≥ 2T1 formula. We have found that –CN (–OH) substituents on electrophilic (nucleophilic) carbons result in improved SF properties when compared to azulene. [ABSTRACT FROM AUTHOR]

When (4n +2) π‐electrons are located in single planar ring, it conventionally qualifies as aromatic. According Hückel's rule, systems possessing ten π‐electrons should be aromatic. Herein we report a series of D5h Li6E5Li6 sandwich structures, representing the first global minima featuring ten π‐electrons E510− ring (E=Si−Pb). However, these π‐electrons localize as five π‐lone‐pairs rather than delocalized orbitals. The high symmetry structure achieved is a direct consequence of σ‐aromaticity, particularly favored in elements from Si to Pb, resulting in a pronounced diatropic ring current flow that contributes to the enhanced stability of these systems. [ABSTRACT FROM AUTHOR]

The bonding pattern of H3+ and its metallic isomers M3+ (M = Li, Na, and K) have been studied through the topological criterion by the quantum theory of atoms in molecules (QTAIM), interacting quantum atoms (IQA) and valence bond (VB) approach at the Coupled Cluster level. The results show that for the studied compounds, it is possible to state that they are not ring-type structures but structures in which the atoms are bound through electrostatic and covalent interactions (in that order of priority) to a non-nuclear attractor (NNA) located in the geometric center of the atomic positions. A series of resonance structures have been proposed following the VB model, including those of the covalent and ionic type with the participation of the NNA, which would explain the computed results. Additionally, a simple way of calculating the percentages of the contribution of each resonance structure using the delocalization and localization indexes is proposed. Calculated values show that the ionic resonance structures have a high contribution in the four studied systems, so it is possible to conclude that these compounds have charge-shift bonds. [ABSTRACT FROM AUTHOR]

In this work, we have revisited the aromaticity of benzyne isomers at the unrestricted density functional theory level (UDFT) using the energetic, magnetic, and delocalization criteria. In addition, this last criterion has also been analyzed employing complete active space (CASSCF) calculations. The results show conservation of aromaticity in these monocycles. Additionally it is observed that this trend is maintained in polycyclic aromatic hydrocarbon derivatives such as biradical didehydrophenanthrenes. Do these results imply a violation of Baird's rule? The answer is No, because this conservation in aromaticity is due to the loss of hydrogen atoms affects only the electronic σ skeleton and exerts a minor influence on the π cloud. Additionally, we have analyzed the relative stability of benzyne isomers and their relationship with experimental ΔES‐T values. According to the literature, the stability of the benzynes in the singlet state is due to an effective interaction between the electrons of the biradical centers; however, this effect is completely reversed in the triplet state, which explains why the para isomer has the lowest ΔES‐T gap. [ABSTRACT FROM AUTHOR]

The chemical bonding of 3C2O and 3N2C is analyzed in this work through the topological quantum approach using the electronic localization function (ELF) at the CASSCF level and by energetic calculations at the CCSD(T) level using four different basis sets. The results show that the dissociation of the molecules occurs via cleavage of the C‐C bond in the case of 3C2O, while in the case of 3N2C, it occurs via cleavage of the N‐C bond. Furthermore, the results obtained with ELF show monosynaptic basins containing excess electrons and disynaptic basins with a low electron population. This leads us to indicate the existence of three‐center‐two‐electron bonds according to previous results. From the valence bond model, a series of resonance structures have been proposed that support our calculations. In addition, the proposed structures have an ionic nature, indicating a charge shift character. [ABSTRACT FROM AUTHOR]

Nowadays, an active research topic is the connection between Clar's rule, aromaticity, and magnetic properties of polycyclic benzenoid hydrocarbons. In the present work, we employ a meticulous magnetically induced current density analysis to define the net current flowing through any cyclic circuit, connecting it to aromaticity based on the ring current concept. Our investigation reveals that the analyzed polycyclic systems display a prominent global ring current, contrasting with subdued semi‐local and local ring currents. These patterns align with Clar's aromatic π‐sextets only in cases where migrating π‐sextet structures are invoked. The results of this study will enrich our comprehension of aromaticity and magnetic behavior in such systems, offering significant insights into coexisting ring current circuits in these systems. [ABSTRACT FROM AUTHOR]

Thermodynamic, kinetic, and chemical bonding analysis at the coupled cluster level has been carried out for a series of hypercoordinated carbon compounds with formula CH4Ng2+ (Ng = He–Rn). Results show that these compounds could be stable at room temperature and Born–Oppenheimer molecular dynamics simulations (BOMD) in conjunction with activation energies indicate high kinetic stability. In addition, all chemical bonding descriptors agree with a strong C–Ng covalent bond and a bonding pattern similar to that of CH5+. Finally, BOMD simulations showed that these compounds are fluxional, with a continuous formation/breaking of H–H and C–H bonds. To the best of the authors' knowledge, these results represent the first series of fluxional compounds possessing a covalent bond between a main group element and a noble gas atom. [ABSTRACT FROM AUTHOR]

The electronic structure, changes in aromatic behavior, and stability of the m-quinone, the least studied member of the benzoquinone family, have been analyzed. Through unrestricted density functional theory calculations, three aromaticity criteria (magnetic, electronic, and geometric), and resonance forms through the valence bond model, we have sought to answer why this isomer prefers the triplet state in its ground state. The answer is given in terms of spin density delocalization and proposed resonance structure contributions. The triplet state presents a higher spin delocalization which can be observed in the condensed values and the higher number of resonance forms contributing to the delocalization. Additionally, using magnetic criteria, we have used a simple but effective model to quantify the contribution of the proposed resonance structures, which have an excellent agreement with the spin density values. [ABSTRACT FROM AUTHOR]