Excited‐State Aromaticity of Gold(III) Hexaphyrins and Metalation Effect Investigated by Time‐Resolved Electronic and Vibrational Spectroscopy

Kim, Jinseok; Oh, Juwon; Soya, Takanori; Yoneda, Tomohiro; Park, Seongchul; Lim, Manho; Osuka, Atsuhiro; Kim, Dongho

doi:10.1002/ange.201913058

Cited by 1 publication

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“…19,73 Furthermore, direct observation of Baird (anti)aromaticity by time-resolved IR spectroscopy in expanded porphyrins revealed that an aromaticity reversal and associated structural changes are completed within the time resolution of the measurements, 200−300 fs. 74,75 In this regard, the results of our simulations provide not only temporal information on the reversal of aromaticity but also an important insight into its applicability to excited-state photochemistry.…”

Section: Resultsmentioning

confidence: 93%

Ultrafast Excited State Aromatization in Dihydroazulene

Shostak

Park

et al. 2023

J. Am. Chem. Soc.

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Excited-state aromatization dynamics in the photochemical ring opening of dihydroazulene (DHA) is investigated by nonadiabatic molecular dynamics simulations in connection with the mixed-reference spin-flip (MRSF)-TDDFT method. It is found that, in the main reaction channel, the ring opening occurs in the excited state in a sequence of steps with increasing aromaticity. The first stage lasting ca. 200 fs produces an 8π semiaromatic S 1 minimum (S 1, min ) through an ultrafast damped bond length alternation (BLA) movement synchronized with a partial planarization of the cycloheptatriene ring. An additional ca. 200 fs are required to gain the vibrational energy needed to overcome a ring-opening transition state characterized by an enhanced Baird aromaticity. Unlike other BLA motions of ππ* state, it was shown that their damping is a characteristic feature of aromatic bond-equalization process. In addition, some minor channels of the reaction have also been discovered, where noticeably higher barriers of the S 1 non/antiaromatic transition structures must be surmounted. These anti-Baird channels led to reformation of DHA or other closed-ring products. The observed competition between the Baird and anti-Baird channels suggests that the quantum yield of photochemical products can be controllable by tipping their balance. Hence, here we suggest including the concept of anti-Baird, which would expand the applicability of Baird rule to much broader situations.

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