| Abstract: | Variable‐temperature NMR and ESR spectroscopic studies reveal that bis(dibenzoa,i]fluorenylidene) 1 possesses a singlet ground state, 1 (S0), while the 90° twisted triplet 1 (T1) is populated to a small extent already at room temperature. Analysis of the increasing amount of paramagnetic 1 (T1) at temperatures between 300 and 500 K yields the exchange interaction Jex/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. |
