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A Thermally Populated, Perpendicularly Twisted Alkene Triplet Diradical
Author(s) -
Wentrup Curt,
RegimbaldKrnel Michèle J.,
Müller Dennis,
Comba Peter
Publication year - 2016
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201607415
Subject(s) - diradical , singlet state , chemistry , alkene , triplet state , paramagnetism , ground state , radical , photochemistry , crystallography , molecule , atomic physics , condensed matter physics , physics , excited state , catalysis , organic chemistry
Variable‐temperature NMR and ESR spectroscopic studies reveal that bis(dibenzo[a,i]fluorenylidene) 1 possesses a singlet ground state, 1 (S 0 ), while the 90° twisted triplet 1 (T 1 ) is populated to a small extent already at room temperature. Analysis of the increasing amount of paramagnetic 1 (T 1 ) at temperatures between 300 and 500 K yields the exchange interaction J ex / h c =3351 cm −1 and a singlet–triplet energy splitting of 9.6 kcal mol −1 , which is in excellent agreement with calculations (9.3 kcal mol −1 at the UKS BP86/B3LYP/revPBE level of theory). In contrast, the zero‐field splitting parameter D is very small (calculated value −0.018 cm −1 ) and unmeasurable.