Stable Diradical on the Dimethyldihydropyrene Scaffold

Abstract

The diradical character in a molecular architecture can be customized primarily in two ways: first, by employing a quinoidal pro-aromatic system with net energy gained by aromatization that compensates for the energy required to generate the diradical species and, second, by employing an antiaromatic system having easily accessible triplet states that impart a diradical character. We have chosen a 14π aromatic framework, Boekelheide's dimethyldihydropyrene, and perturbed its aromaticity through the construction of its quinoidal form. The perturbed aromaticity was evident from the bond alteration in the X-ray diffraction structure, 1 H nuclear magnetic resonance chemical shifts, and quantum chemical calculations. The aromaticity was restored as the system underwent a transition to the biradical structure centered on two exocyclic carbons. In addition, upon photoexcitation and without using an external reducing reagent, the diradical could be converted to a radical anion and dianion form easily when dimethylformamide was used as a solvent.

Cyano disubstituted tetrabenzoindeno[2,1-a]fluorene: open-shell or closed-shell?

“…3b), which is a consequence of reduced population of magnetically active triplet species at lower temperatures. 18 A careful fitting of the VT-EPR data using the Bleaney–Bowers equation 19 gave a Δ E S–T = −0.97 kcal mol −1 for 6 (Fig. S11a, ESI†), suggesting singlet OS ground state, which is in line with VT-EPR in solution (Δ E S–T = −1.73 kcal mol −1 , Fig.…”

Light-driven modulation of electrical conductance with photochromic switches: bridging photochemistry with optoelectronics

“…82 We investigated the Our group has also recently embarked on an exploration of materials on the DHP scaffold where radicals can be generated. 83 The radical-containing DHP systems may lead to superior conducting materials with photomodulation properties that are currently under our investigation.…”

From Visible to Near–Infrared Light–Triggered Photochromism: Negative Photochromism

“…Similar to a stilbene linked with an ethylene group, dimethyldihydropyrene exhibits negative photochromism, transitioning from a colored closed isomer (7c) to colorless open isomer (7o) (Scheme 7). The relative stability of the open and closed isomers is inverted from DAE, because of the stabilization at aromatic 14π-electron system in the closed form 7c [47]. [48].…”