DOES INTERELECTRONIC EXCHANGE BECOME VANISHINGLY SMALL AS PLANAR CONJUGATION LENGTH GROWS VERY LARGE?

Bis(arylnitrenes) are largely controlled by one-center interactions on each of the nitrene spin sites. We are looking for evidence that complete isolation of the triplet mononitrene sites could occur in a nominally conjugated dinitrene. We think that we are reaching that point in the progression of conjugation shown in the dinitrenes below. Note the lack of a peak in the pink zone of the green spectrum/molecule. The pink zone in the ESR spectral region is where quintet dinitrene peaks usually come.


Spectra by Richard Walton (1996)
Spectra both obtained in frozen 2-MTHF at 77 K, approx 9.5 GHz frequencies.

Computational work carried out by Jon Sanborn and Andrew S. Ichimura further demonstrates that large spin density sites reside on the nitrogen atoms of the p,p'-diiminediyl systems. However, the computations also show that the singlet-triplet gap decreases with increasing conjugation length. For more information, see Paul M. Lahti, Andrew S. Ichimura, Jon A. Sanborn, "Methodologies for Computational Studies of Quininoidal Diiminediyls: Biradical vs. Dinitrene Behavior", J. Phys. Chem., Part A, 105, 251-260 (2001).