Redox Associated variation of Hückel Aromaticity from Lactam Embedded Smallest Antiaromatic trans-Doubly Nconfused Porphyrins: Synthesis and Characterization.

High yield synthesis, spectroscopic and solid state structural proof of the lactam embedded
smallest ever metal free stable Hückel antiaromatic trans-doubly N-confused [16] porphyrins
are reported. These new facets of trans-doubly N-confused porphyrins have been anticipated
to exhibit the redox associated variation of Hückel aromaticity as a mere consequence of the
amido-like structures of the N-confused N-methyl pyrrole rings of the macrocycles. Strong
aromaticity upon NaBH4 reduction leading to resonance dipolar structure of the
[18]conjugated system as the reduced congener with concomitant Hückel topology are the important highlights. Excellent agreement between experimental spectroscopic measurements
and the theoretically determined properties elucidate aromaticity switching upon chemical
reduction. Recent years have witnessed an upsurge of demand for the experimental
realization of stable antiaromatic systems due to their versatile applications in the material
science. The conformational rigidity and the enriched stability of these novel 16
antiaromatic doubly N-confused porphyrins might entitle these macrocycles towards such
applications.