Synthesis and Physical Properties of Trioxotriangulene Having Methoxy and Hydroxy Groups at α-Positions: Electronic and Steric Effects of Substituent Groups and Intramolecular Hydrogen Bonds

Abstract

New 4,8,12-trioxotriangulene (TOT) neutral radical derivatives having three methoxy and hydroxy groups at the α-positions were synthesized, and the substituent effects on the electronic spin and redox properties were elucidated in the theoretical and experimental methods. Due to the small SOMO coefficients at the α-positions of TOT, the methoxy groups in the TOT neutral radical had negligible effects on the electronic spin structure and redox ability. On the other hand, methoxy groups greatly increased the LUMO energy having large coefficients at α-positions and, thus, caused a remarkable negative-potential shift of the redox wave of anion species involving the dianion and trianion species. Converting the methoxy groups to hydroxy groups caused a dramatic change in the electronic structure of TOT, where the intramolecular hydrogen bonds between hydroxy groups and oxo groups strongly attracted a minus charge on the TOT skeleton. The HOMO energy of the monoanion species was significantly reduced, causing a blue shift of the HOMO–LUMO transition and an anodic shift of the redox potential. In addition, due to the steric repulsion smaller than that of the methoxy group, the hydroxy derivative showed a more planar molecular structure and a strong π-stacking ability.

Electro-optical π-radicals: design advances, applications and future perspectives

“…Intramolecular hydrogen bonding also enhanced molecular planarity and strong intermolecular p-stacking, which was observed as redshifted low-energy absorption band peaking at 1416 nm in the solid state. 177 Similar formation of diamagnetic p-dimers was recently reported for a silyl substituted TOT derivative by Morita et al 180 Self-assembly of the radical by polycondensation of the silyl groups gave rise to microporous organosilanes that gained additional stabilisation by spin delocalisation throughout the porous structure. Porous radical assemblies with reversible multi-stage redox reactions may find uses, for example, as very high charge-density materials in energy storage, and it would be exciting to see future progress towards this direction.…”

“…Characteristics of other phenalenyl derivatives like 19 and 20, developed by Morita et al, 154,169 and larger planar radicals like triangulenes are in many ways analogous to the smaller phenalenyls. Morita et al [170][171][172][173][174][175][176][177][178] have utilised the added stability of trioxotriangulene (TOT) and dicyanomethyl substituted triangulene 21 (Scheme 7), which have four and eight reversible redox states, respectively, in a narrow potential range due to their degenerate LUMOs that are also energetically close to their SOMO. These radicals are electrically conductive and This journal is © The Royal Society of Chemistry 2022 air-stable in the solid state, and even more so in their corresponding anionic forms (p-stacked crystals of 21 and TOT decompose at 195 and 4300 1C in air, respectively), making them very attractive for use as rechargeable energy storage materials in organic batteries.…”

From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals

“…The crystal of this compound contained 1D π-stacks with an equidistant stacking distance of 3.29 Å. 231 In addition to various substituted TOTs, 232,233 TOT (R = H) 234 and dicyanomethylene-substituted triangulene derivative (R = t-Bu) 235 were prepared. For TOT (R = H), the onset of thermal decomposition (TGA), defined as 1% mass loss, is perhaps at about 100−150 °C, compared to >300 °C for TOT (R = t-Bu); similar findings were obtained by UV−vis spectral follow-up in solution saturated with air with half-lives of the radicals being ca.…”

Synthesis and Properties of a Through-Space Interacting Diradicaloid

“…In addition, studies have been carried out on another type of diradicaloid, in which two radical sites interact through space in a manner that is governed by the distance between the radical sites and the overlap integral between singly occupied molecular orbitals (SOMOs) of the radical sites. Examples of these types of diradicals are 1,3-diyls, , benzynes, − and radical π-dimer − (pancake-bonded dimer − ). However, owing to the limited number of through-space interacting diradicaloids probed thus far, questions about their bonding characteristics and physical properties remain unanswered.…”