Molecule Isomerism Modulates the Diradical Properties of Stable Singlet Diradicaloids

Abstract

Inclusion of quinoidal cores in conjugated hydrocarbons is a common strategy to modulate the properties of diradicaloids formed by aromaticity recovery within the quinoidal unit. Here we describe an alternative approach of tuning of diradical properties in indenoindeno­dibenzo­thiophenes upon anti → syn isomerism of the benzothiophene motif. This alters the relationship of the S atom with the radical center from linear to cross conjugation yet retains the same 2,6-naphtho conjugation pattern of the rearomatized core. We conduct a full comparison between the anti and syn derivatives based on structural, spectroscopic, theoretical, and magnetic measurements, showing that these systems are stable open-shell singlet diradicaloids that only access their triplet state at elevated temperatures.

Modulating the ground state, stability and charge transport in OFETs of biradicaloid hexahydro-diindenopyrene derivatives and a proposed method to estimate the biradical character

“…These results are in line with the behaviours of anti and syn-IIDBT. 13,14 According to our theoretical calculations, syn-IIDBT has a DE S-T close to those of linear-and anti-HDIP and the signal broadening in 1 H NMR of syn-IIDBT starts at 75 C which is close to the temperature obtained for linear-and anti-HDIP (80 C). 14 In a similar manner, HDIP and anti-IIDBT have similar DE S-T and the signal broadening of protons in 1 H NMR starts at similar temperatures (125 C and 120-140 C for anti-IIDBT and HDIP, respectively).…”

“…Thus, IIDBT and HDIP derivatives should have a similar biradical character since the emergence of the biradical character contribution in the ground state is related to the proaromaticity/aromatic stabilization of the biradical structure, the band gap and the number of p-electrons. 14…”

“…1 Several kinds of delocalized open-shell compounds that can be written with a Kekulé resonance form have been prepared based on aromatic six-membered rings as acenes longer than 6 rings, 2 anthenes, 3 peri-acenes, 4 rylene ribbons 5 and acenoacenes 6 or based on quinoidal compounds comprising only 6-membered rings (6-MR) as zethrene derivatives 7 or with the inclusion of two 7-membered rings (7-MRs) as heptalene derivatives 8 or 5membered rings in the p-conjugated core as bisphenalenyl derivatives 9 and diindeno-based PHs. [10][11][12][13][14][15][16] Among them, diindeno-based PHs are the most developed owing to their rather facile preparation at least for the small members. Since Kekuléan biradicaloid systems are resonance hybrids between the closed-and the open-shell forms, the contribution of each form in the ground state is described by the biradical character a UMR CNRS 8180, UVSQ, Institut Lavoisier de Versailles, Université Paris-Saclay, 45 avenue des Etats-Unis, 78035 Versailles Cedex, France.…”

Quinoidal Azaacenes: 99 % Diradical Character

“…For the regioisomers, benzannulated 1M represents an ortho ‐quinodimethane with a more pronounced disjunction of beta‐connected bithiophenylenes . Thus, its diradical character is higher than that of the p ‐QDM ( y 0 =0.51).…”

Quinoidal Azaacenes: 99 % Diradical Character

“…For the regioisomers, benzannulated 1M represents an ortho-quinodimethane with a more pronounced disjunction of beta-connected bithiophenylenes. [32] Thus, its diradical character is higher than that of the p-QDM (y 0 = 0.51).…”