|Posted on February 16, 2021 at 3:45 AM|
The first article of 2021 has been accepted in Angewandte Chemie. The main author is Sílvia Escayola, who is doing her joint PhD between the DIPC (working with Dr. Eduard Matito) and the Universitat de Girona (Prof. Miquel Solà and Dr. Albert Poater). The work is a collaboration between these groups and photophysics group of Dr. Casanova (DIPC) and the group of Henry Ottosson.
Using time-dependent density functional theory, we considered a series of symmetrically substituted conjugated rings that can generate Baird aromaticity in the lowest-lying excited states. From these results, we establish general guidelines for the rational design of molecules with excited state Hückel or Baird aromaticity in pro-aromatic quinoidal compounds. Namely, two main strategies to promote a high Baird aromatic character of the central ring, are suggested: (i) employing anionic and small conjugated rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents, or (ii) electron deficient conjugated rings with exocyclic electron-donor substitution. Our results also show that some recent experimental interpretation [Kim et al. Nature Commun. 2019, 10, 4983] of the excited state of TMTQ should be revised because low-lying excitations of symmetrically substituted conjugated rings including TMTQ hold very weak charge transfer character.
S. 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, ASAP (doi: 10.1002/anie.202100261). The paper is also available at chemrxiv.