On 19th June 2021, Karolina Urbanowicz started a visit of six weeks to the DiMoCat group financed by HPC-Europa3. The research project of Karolina, which is supervised by Dr. Antony J. Stasyuk and Prof. Miquel Solà, is primarily aimed at the investigation of conformational-property landscape in triplet photosensitizers derived from metal-free organoboron complexes with semi-rigid spiro architecture and boron atom separating donor and acceptor parts of the molecule. These systems are very effective photocatalysts in the oxidation reactions mediated by singlet oxygen. We expect that understanding of their nature will lead to new opening in the field of metal-free photosensitizers with potent application in catalysis, photodynamic therapy or cancer treatment and antimicrobial photodynamic therapy.

We wish Karolina good luck and great successes in her project!

From left to right, Karolina, Anton and Miquel in the IQCC.

A recent paper (Kim et al. Nature Commun. 2019, 10, 4983) claims that there is a double charge transfer in the first singlet excited singlet state in TMTQ (an oligomer composed of a central 1,6-methano[10]annulenes, M10A, and 5-diacyanomethyl-thiophene exocyclic groups, see Figure 1) that is stabilized by the Baird aromaticity acquired by the central M10A ring. In a previous work (Jorner et al. Chem. Eur. J. 2016, 22, 2793), some of us found that the charge transfer in the first excited singlet and triplet states in TMTQ is minor and that the central ring in these low-lying excited states is a Hückel-Baird hybrid with a ca. 85% of Hückel and 15% of Baird character. In the light of the new existing experimental data, Claire Tonnelé and Prof. Henrik Ottosson of the Uppsala University, Dr. David Casanova and Dr. Eduard Matito of the Donostia International Physics Center (previous DiMoCat member), and Sílvia Escayola, Dr. Albert Poater, and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona decided to reinvestigate the problem using (time-dependent) density functional theory methods. We considered not only TMTQ but also a series of symmetrically substituted conjugated rings that can generate Baird aromaticity in the lowest-lying excited states. This work shows that the interpretation by Kim et al. needs to be revised because low-lying excitations of symmetrically substituted conjugated rings including TMTQ hold very weak charge transfer character. Our computational results also allow us to establish general guidelines for the rational design of molecules with excited state Hückel/Baird aromaticity in pro-aromatic quinoidal compounds We found that high Baird character of the central ring is achieved only with anionic and small conjugated central rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents. Our study aims to warn about the need to make correct interpretations of the experiments in this growing area of research, as only then can the excited state aromaticity concept develop in a useful tool for the design of high-performance organic electronic devices.

Figure 1. Quinoidal, diradical, and ionic resonance structures of importance for TMTQ (10R-T) involved in the description of S₀, S₁, and T₁ states.

Escayola, C. Tonnelé, E. Matito, A. Poater, H. Ottosson*, M. Solà* and D. Casanova*. Guidelines for Tuning the Excited State Hückel-Baird Hybrid Aromatic Character of Pro-Aromatic Quinoidal Compounds. Angew. Chem. Int. Ed., 2021, DOI: 10.1002/anie.202100261.

The FRONT COVER of issue number 83 of volume 56 refers to the recently published article “All-metal Baird aromaticity”. The work has been carried out by Prof. Jun Zhu at the University of Xiamen and Dandan Chen, Dr. Dariusz W. Szczepanik, and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona. The cover is the result of the artistic inspiration of Dandan Chen. The paper has been highlighted by ChemistryWorld. Inthe same issue, others members of DiMoCat have published another paper entitled “Photoinduced electron transfer in nanotube⊃C₇₀ inclusion complexes: phenine vs. nanographene nanotubes“.

ICREA announced the list of winners of the ICREA Acadèmia awards 2019, among which are three (!!!) names from the University of Girona: Sebastià Puig (Engineering), Anna Company and Albert Poater (both IQCC and Chemistry). Albert Poater belongs to DIMOCAT group.

In search of green or sustainable chemistry there are different objectives to achieve, and already achieve successfully one already represents a step forward to improve the world that surrounds us. Here, in this collaborative work between the experimental team of the University of Normandy (France) led by Prof. Jean Luc Renaud, and from Girona, Dr. Albert Poater the computational complementary part, has been able to achieve not only find a catalyst capable of fixing CO₂, but to find out one that is not based on noble metals, expensive, and of high toxicity, and furthermore, dealing with water as a solvent. An iron, most abundant metal catalyst of the Earth’s layer has been employed.  Overall, a highly efficient, stable, phosphine-free, and easy-to-synthesize iron catalyst system for the reduction of CO₂, hydrogenocarbonate, and carbonate in pure water is reported.

Coufourier, Q. Gaignard-Gaillard, J.-F. Lohier, A. Poater, S. Gaillard, J.-L. Renaud; “Hydrogenation of CO2, Hydrogenocarbonate, and Carbonate to Formate in Water using Phosphine Free Bifunctional Iron Complexes”; ACS Catal. 2020, 10, 2108-2116. DOI: 10.1021/acscatal.9b04340