Synthesis and Halochromic Behavior of π-Extended Azuleno[1’,2’:4,5]pyrrolo[2,1- <i>b</i> ]quinazoline-6,14-diones Solubilized by Mesityl Substituent

Abstract π-Extended azuleno[1’,2’:4,5]pyrrolo[2,1-b]quinazoline-6,14-diones, azulene analogs of tryptanthrin, were synthesized by (1-pyrenyl)ethynyl substitution, introduction of electron-donating aryl substituents, and 1,1,4,4-tetracyanobutadiene (TCBD) substitution of the corresponding azulene-fused skeletons possessing sufficient solubilities. (1-Pyrenyl)ethynyl substitution was successfully established by Pd-catalyzed Sonogashira cross-coupling reaction of the 2-iodo and 12-iodo derivatives solubilized by mesityl substituent at the 9-position. Introduction of electron-donating aryl substituents was established by Suzuki-Miyaura cross-coupling reaction of the 2-iodo derivative with arylboronic reagents bearing either a p-amino or p-hydroxy substituent. Electron-withdrawing TCBD substitution at the 2-position was realized via 2-(phenylethynyl) derivative with N,N-dibutylamino function at the p-position as a solubilizing group, which was transformed into the corresponding TCBD derivative by the reaction with tetracyanoethylene (TCNE). These π-extended azulene analogs of tryptanthrin were featured by spectroscopic and voltammetric analyses. Elucidation of the halochromic behavior of the π-extended derivatives upon the addition of trifluoroacetic acid to a dichloromethane solution resulted in a marked bathochromic shift of the longest-wavelength absorption bands, extending into the near infrared region.