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Triplet Energy of 2, 2‐Dimethylisoindene from Electron‐Energy‐Loss Spectroscopy and Photoinduced Triplet Energy Transfer
Author(s) -
Allan Michael,
Asmis Knut R.,
Houar Sarah El,
Haselbach Edwin,
Capponi Marco,
Urwyler Bernhard,
Wirz Jakob
Publication year - 1994
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19940770609
Subject(s) - chemistry , excited state , triplet state , singlet fission , singlet state , atomic physics , spectroscopy , flash photolysis , physics , reaction rate constant , quantum mechanics , kinetics
The excited electronic states of 2, 2‐dimethylisoindene ( 1 ) have been studied by electron‐energy‐loss spectroscopy. Its vertical gas‐phase triplet (1 3 B 2 ), and singlet (1 1 B 2 ) excitation energies are 1.61 and 3.19 eV, respectively. The excited states are thus lowered by 0.49 eV and 1.21 eV, respectively, when compared to the corresponding states of (all‐ E )‐octatetraene, which serves as a reference compound. These shifts are partially reproduced by ZINDO calculations. The spectra give no evidence for a 2 1 A g state below the 1 1 B 2 state, but this lack of observation does not exclude its existence. The lowest triplet state T 1 ( 1 ) was further characterized by flash photolysis. T 1 ( 1 ) was observed as a transient intermediate, λ ≤ 350 nm, with a lifetime of 8 m̈s in degassed hexane. The adiabatic excitation energy of T 1 ( 1 ) was bracketed to the range of 1.1 ± 0.1 eV by energy‐transfer experiments. Relationships between the energies of the lowest excited singlet and triplet states of 1 and the lowest excited doublet state of its radical cation \documentclass{article}\pagestyle{empty}\begin{document}${1}^{+\kern0pt {.}}$\end{document} – essentially a non‐ Koopmans ' state – are discussed.