Bicyclic

[…] substitution of a carboxylate would be expected to destabilize the dritterionic mesomer that contributes to the singlet valence bond description as the benzyne geometry becomes more bicyclic.

These geometries are almost reversed in the triplets. The 1,3-borazyne (III) shows more bicyclic character than the corresponding m-benzyne

On the basis of a comparison of calculated and measured IR data, the 2 B 2 state could undoubtedly be discarded in favor of a more bicyclic geometry