Tuning Spin-State Preference by Substituents:  A Case Study of Thianthrene Dication

Abstract

We report an effective example of π-conjugated systems showing the reverse spin-state preferences depending on the substitution patterns. It is shown that 2,3,7,8-and 1,4,6,9-tetramethoxy-substituted thianthrenes have different electronic structures owing to destabilization of the specific frontier molecular orbitals. On the basis of the hybrid Hartree-Fock/density functional method (B3LYP/6-31G*), the singlet-triplet energy gaps are estimated to be -10.7 and +8.8 kcal/mol for 2,3,7,8-and 1,4,6,9-substituted thianthrenes, respectively. Moreover, it is also shown that nuclear independent chemical shift (NICS), the index of local aromaticity for polycyclic π-conjugated systems, is closely correlated with the spin-state preferences of the present thianthrene system.

Density Functional Theory Study of Tetrathiafulvalene and Thianthrene in Acetonitrile: Structure, Dynamics, and Redox Properties

“…Gas-phase calculations on TH predict a ground-state geometry of butterfly shape with a folding angle around the S-S axis (see Figure 1 for a definition) of ∼129°, in good agreement with a recent X-ray structure. [25][26][27]69 However, in benzene solution and in an ordering liquid (Merck Nematic Phase IV) folding angles of ∼140°have been reported. 70,71 Our results in the liquid, shown in the upper panel of Figure 6, are consistent with this shift to larger angles.…”

“…24 Additionally, its butterfly shape (Figure 1) has triggered a number of theoretical investigations. [25][26][27] MeCN is a commonly employed aprotic solvent that has not yet been characterized by ab initio molecular dynamics simulation. In the context of electron-transfer reactions, it is noteworthy that MeCN is a typical solvent in dye-sensitized solar cells.…”

The effect of substituents on electronic states’ ordering in meta-xylylene diradicals: Qualitative insights from quantitative studies

“…The effect of substituents on the singlet-triplet gaps in diradicals has been studied by many theoretical and experimental groups. [6][7][8][9][10][11][12][13][14] For example, for a 1,4-didehydrobenzene diradical, Clark and Davidson 6 found that substituents, which strongly interact with the benzyne system, do not interact with the space, and are only weakly electronegative, should yield the smallest singlet-triplet energy differences and might lead to the triplet ground state. Berson and co-workers 8,9 reported that electron-withdrawing substituents modulate the singlet-triplet gaps of the singlet tetramethyleneethane-type diradical.…”

“…Berson and co-workers 8,9 reported that electron-withdrawing substituents modulate the singlet-triplet gaps of the singlet tetramethyleneethane-type diradical. Ito et al 10 reported examples of -conjugated trianthrene systems showing the reverse spin-state preferences depending on the substitution patterns. Geise and Hadad 11 found that for ortho-, meta-, and para-substituted phenylcarbenes aromatic ring substituents have a large effect on the singlet-triplet splitting.…”

Bisanthra-thianthrene: synthesis, structure and oxidation properties

“…1) and the bilateral benzene rings have no electronic interaction with each other in the neutral state, while the two-electron oxidation of THA gives the closed-shell dication of THA (THA 2+ ) with a planar 14p aromatic system similar to anthracene. [15][16][17] Bisanthra-thianthrene (BA-THA) is a larger family of THA. The investigation of oxidation behavior of BA-THA is important for understanding the fundamental properties of dithiaacenes.…”