Tropylium cation-fused aromatic [26]dicarbaporphyrinoids with NIR absorptions: Synthesis, spectroscopic and theoretical characterization

Abstract

An easy and efficient synthetic methodology for two hitherto unknown tropylium-cation-fused Hückel aromatic [26] dicarbaporphyrinoids has been developed by acid-catalyzed Lindsey type condensation of bithiophene/biselenophene diol with azulene using BF3 · Et2O followed by oxidation with chloranil and/or DDQ. Both the macrocycles have been achieved in moderately good yields. Their structures, aromaticity and optical properties have been elucidated by NMR, UV-vis-NIR spectroscopic analyses and in-depth theoretical calculations. Both the macrocycles exhibited strongly diatropic characteristics with the UV-vis spectra closely resembling the spectra for true porphyrins. Detailed structural analyses using 1H–1H COSY, ROESY and DFT level theoretical investigations indicated fully conjugated [26][Formula: see text] main conjugation pathway being benefitted by the tropylium character of the seven membered rings.