Computational study of Aromaticity in Porphyrinoid Systems and Photosensitizers from Chemical Bonding Descriptors

291 p.La presente tesis está dividida en dos bloques. El primer bloque se centra en una de las propiedadesafectadas por el error de deslocalización, la aromaticidad, presente en algunas aproximaciones delfuncional de la densidad. Se estudia el carácter aromático de sistemas una familia de porfirínas simples,una serie de anulenos y un anillo de seis porfirínas. También se discute el método computacionalapropiado para caracterizar la estructura electrónica de moléculas aromáticas medianas y grandes.Siguiendo la misma línea, en el segundo bloque de la tesis se han examinado diferentes familias defotosensibilizadores y catalizadores para diseñar un protocolo riguroso para el estudio de la estructuraelectrónica, la simulación de espectros UV-Vis y para el cálculo de potenciales redox. Losfotosensibilizadores son moléculas captadoras de luz que presentan excitaciones de transferencia decarga. La simulación de estas excitaciones está afectada también por las deficiencias de lasaproximaciones al funcional de la densidad

Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins.M.A. and I.C.R. wish to acknowledge the VUB for a Strategic Research Program awarded to ALGC. The resources and services used in this work were provided by the Flemish Supercomputer Center (VSC), funded by the Research Foundation - Flanders (FWO), and the Flemish Government. I.C.R. acknowledges co-funding from the European Union′s Horizon 2020 research and innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. It has been also supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), Gobierno Vasco (IT1346-19, IT1254-19, and PIBA19-0004), and the DIPC (DIPC_INV_003132). Open Access funding provided by University of Basque Country

How Aromatic Are Molecular Nanorings? The Case of a Six-Porphyrin Nanoring

Large conjugated rings give rise to novel promising structures that can sustain persistent currents at low temperatures even in the presence of strong magnetic fields. One of the most interesting such molecules was recently synthesized [Anderson et al., Nature, 2017, 541, 3512] in the form of a six-porphyrin nanoring structure, which, according to the authors, in its +6-oxidation state (c-P66+) sustained an aromatic ring current involving 78π electrons; one of the largest aromatic rings ever produced. In this paper, we have provided compelling evidence that this molecule is not aromatic, as it was incorrectly inferred from computational calculations that suffer from large delocalization errors. A thorough analysis of four oxidation states of the six-porphyrin nanoring re- veals that the main reason behind the poor aromaticity of these nanorings is the low delocalization in the transition from the porphyrins to the bridging butadiyne linkers, which disrupts the overall conjugated circuit. These results highlight the importance of choosing an adequate computational method to study large conjugated molecules and the appropriate aromaticity descriptors to identify the part of the molecule that is responsible for the loss of aromaticity. We believe the strategy here employed will be helpful in designing new large aromatic molecular nanorings. </div

How aromatic are molecular nanorings? The case of a six-porphyrin nanoring

Large conjugated rings with persistent currents are novel promising structures in molecular-scale electronics. A six-porphyrin nanoring structure that allegedly sustained an aromatic ring current involving 78π electrons was recently synthesized. We provide here compelling evidence that this molecule is not aromatic, contrary to what was inferred from the analysis of 1H-NMR data and computational calculations that suffer from large delocalization errors. The main reason behind the absence of an aromatic ring current in these nanorings is the low delocalization in the transition from the porphyrins to the bridging butadiyne linkers, which disrupts the overall conjugated circuit. These results highlight the importance of choosing a suitable computational method to study large conjugated molecules and the appropriate aromaticity descriptors to identify the part of the molecule responsible for the loss of aromaticity.This work has been supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB-I00, EUR2019-103825, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), and Gobierno Vasco (IT1346-19, IT1254-19, PRE_2016_1_0159, and PIBA19-0004). E.R.C. acknowledges funding from the Juan de la Cierva program IJCI-2017-34658.Peer reviewe

Reply to the Correspondence on "How Globally Aromatic Are Six-Porphyrin Nanorings?"

A recent article by Anderson and co-workers challenges our conclusions on the aromaticity of the four oxidation states of a butadiyne-linked six-porphyrin nanoring, ased on the experimental 1H-NMR data and some recent calculations they have performed using the BLYP35 unctional. Here, we show that BLYP35 should be taken with caution and demonstrate that the indirect evidence of a ring current from experimental 1 H-NMR data is not a definite proof of aromaticity

New Electron Delocalization Tools to Describe the Aromaticity in Porphyrinoids

International audienceThe role of aromaticity in porphyrinoids is a current subject of debate due to the intricate structure of these macrocycles, which in some cases adopt Hückel, Möbius and even figure-eight conformers. One of the main challenges in these large π-conjugated structures is identifying the most conjugated pathway because, among aromaticity descriptors, there are very few that can be applied coherently to this variety of conformers. In this paper, we have investigated the conjugated pathways in nine porphyrinoid compounds using several aromaticity descriptors, including BLA, BOA, FLU and HOMA, as well as the recently introduced AV1245 and AVmin indices. All the indices agree on the general features of these compounds, such as the fulfillment of Hückel's rule or which compounds should be more or less aromatic from the series. However, our results evince the difficulty in finding the most aromatic pathway in the macrocycle for large porphyrinoids. In fact, only AVmin is capable of recognizing the annulene pathway as the most aromatic one in the nine studied structures. Finally, we study the effect of the exchange in DFT functionals on the description of the aromaticity of the porphyrinoids. The amount of exact exchange quantitatively changes the picture for most aromaticity descriptors, AVmin being the only exception that shows the same qualitative results in all cases

New Electron Delocalization Tools to Describe the Aromaticity in Porphyrinoids

International audienceThe role of aromaticity in porphyrinoids is a current subject of debate due to the intricate structure of these macrocycles, which in some cases adopt Hückel, Möbius and even figure-eight conformers. One of the main challenges in these large π-conjugated structures is identifying the most conjugated pathway because, among aromaticity descriptors, there are very few that can be applied coherently to this variety of conformers. In this paper, we have investigated the conjugated pathways in nine porphyrinoid compounds using several aromaticity descriptors, including BLA, BOA, FLU and HOMA, as well as the recently introduced AV1245 and AVmin indices. All the indices agree on the general features of these compounds, such as the fulfillment of Hückel's rule or which compounds should be more or less aromatic from the series. However, our results evince the difficulty in finding the most aromatic pathway in the macrocycle for large porphyrinoids. In fact, only AVmin is capable of recognizing the annulene pathway as the most aromatic one in the nine studied structures. Finally, we study the effect of the exchange in DFT functionals on the description of the aromaticity of the porphyrinoids. The amount of exact exchange quantitatively changes the picture for most aromaticity descriptors, AVmin being the only exception that shows the same qualitative results in all cases

Light-Driven Reduction of Aromatic Olefins in Aqueous Media Catalysed by Aminopyridine Cobalt Complexes.

A catalytic system based on earth-abundant elements that efficiently hydrogenates aryl olefins using visible light as driving-force and H2O as the sole hydrogen atoms source is reported. The catalytic system involves a robust and well-defined aminopyridine cobalt complex and a heteroleptic Cu photoredox catalyst. The system shows the reduction of styrene in aqueous media with a remarkable selectivity (> 20000) versus water reduction (WR). Reactivity and mechanistic studies support the formation of a [Co-H] intermediate, which reacts as a hydrogen transfer agent (HAT). Synthetically useful deuterium-labelled compounds can be straightforwardly obtained by replacing H2O with D2O and using only catalysts based on earth-abundant elements. Moreover, the dual photocatalytic system and the photocatalytic conditions can be rationally designed to tune the selectivity for aryl olefin vs aryl ketone reduction; not only by changing the structural and electronic properties of the cobalt catalysts, but also by modifying the reduction properties of the light-harvesting syste

Deciphering the chemical bonding of the trivalent oxygen atom in oxygen doped graphene

Recently, planar and neutral tricoordinated oxygen embedded in graphene has been imaged experimentally (Nat. Commun., 2019, 10, 4570–4577). In this work, this unusual chemical species is studied utilizing a variety of state-of-the-art methods and combining periodic calculations with a fragmental approach. Several factors influencing the stability of trivalent oxygen are identified. A σ-donation and a π-backdonation mechanism between graphite and oxygen is established. π-Local aromaticity, with a delocalized 4c–2e bond involving the oxygen atom and the three nearest carbon atoms aids in the stabilization of this system. In addition, the framework in which the oxygen is embedded is crucial too to the stabilization, helping to delocalize the “extra” electron pair in the virtual orbitals. Based on the understanding gathered in this work, a set of organic molecules containing planar and neutral trivalent oxygen is theoretically proposed for the first time.This work was supported by funding provided by Gobierno Vasco-Eusko Jaurlaritza (IT1584-22). This work was also supported by grant PID2019-107338RB-C66 and PID2020-114754GA-I00, funded by MCIN/AEI/10.13039/501100011033, and PID2022-140845OB-C66, funded by MCIN/AEI/10.13039/501100011033 and FEDER. In addition, the work was supported by the Spanish Research Agency and the European Union NextGenerationEU/PRTR under Contract No. TED2021-132388B-C44, and the European Union (EU) H2020 program through the FET Open project SPRING (Grant Agreement No. 863098). A. G.-L. also acknowledges the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government. A. U. gratefully thanks Eusko Jaurlaritza for his predoctoral grant. I. C. R. acknowledges co-funding from the European Union's Horizon 2020 Research and Innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. We also thank DIPC and SGI-IZO-SGIker (UPV/EHU) for the generous allocation of computational resources. The authors thankfully acknowledge also the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (QHS-2022-2-002 and QHS-2022-3-0015)