Modulation of Open‐shell Characters of Amine‐inserted Diphenoquinones via Structural Modification

Abstract

In this study, a series of triphenylamine derivatives with two 2,6-diphenylphenoxy radicals (2 a-d), which could be regarded as amine-inserted diphenoquinones have been synthesized and investigated their structures and electronic properties. The structures of 2 a-d were confirmed by single-crystal X-ray analysis, showing the characteristic bond length alternation patterns for closed-shell quinoids. The solutions of 2 a-d exhibited clear ESR signals even at room temperature, indicating their thermally accessible diradical states. The NMR and ESR measurements showed that the diradical character of 2 a-d were increased in the order of 2 a<2 b<2 c<2 d, well-reproduced by theoretical calculations. The results of this work strongly suggest that the diradical character of this class of compounds could be tuned by changing the substituent on the central nitrogen atom.

A polycyclic aromatic hydrocarbon diradical with pH-responsive magnetic properties

“…By tting the values of IT as a function of T using the modied Bleaney-Bowers equation (Fig. 6b), 48 a DE S-T value of À0.95 kcal mol À1 was estimated for BCHF1, which was in a reasonable agreement with the calculated value (À1.84 kcal mol À1 ). Also, such a singlet-triplet energy gap was much smaller compared to those reported for various studied indeno-uorene isomers, 28,43 suggesting that a more pronounced diradical propensity was manifested by BCHF1.…”

Cyclobis(7,8‐(para‐quinodimethane)‐4,4′‐triphenylamine) and Its Cationic Species Showing Annulene‐Like Global (Anti)Aromaticity

“…Although CBQT can be viewed as ac ombined macrocycle of two Thielesh ydro- carbons [13] linked by two Natoms,bond-length analysis shows that ring Bisnot atypical quinoidal structure (Figure 1e), in particular,t he bonds r 10 [1.444(2) ]a nd r 12 [1.391(3) ]a re longer than common C À Cdouble bonds (1.34 ). [14] Harmonic oscillator model of aromaticity (HOMA) values, [15] calculated based on the X-ray bond lengths,o ft he rings Aa nd Ba re 0.82 and 0.96, respectively,i ndicating that both canonical forms Aa nd B (Scheme 1b)c ontribute significantly to ground-state geometry.A sar esult, cyclic p-conjugation is attained. All these data indicate that p-conjugation goes through the Na toms,l ike that in some recently reported Nbridged diradicaloids.…”

“…All these data indicate that p-conjugation goes through the Na toms,l ike that in some recently reported Nbridged diradicaloids. [14] Harmonic oscillator model of aromaticity (HOMA) values, [15] calculated based on the X-ray bond lengths,o ft he rings Aa nd Ba re 0.82 and 0.96, respectively,i ndicating that both canonical forms Aa nd B (Scheme 1b)c ontribute significantly to ground-state geometry.A sar esult, cyclic p-conjugation is attained. Moreover, ring Aa nd ring Bh ave at ilted angle of 22.78 8 and 31.68 8 with respect to the plane determined by six connecting meso Cand Na toms (see Figures S15 and S16 in the Supporting Information), implying that ring Ah as better conjugation than ring B.…”