1,2,3,4-Tetrahydro-1,4,5,8-tetraazaanthracene revisited: properties and structural evidence of aromaticity loss

Abstract

The synthesis and properties of 1,2,3,4-tetrahydro-1,4,5,8-tetraazaanthracene (THTAA) – a heterocycle involving both >N–H donating and =N– accepting moieties – have been reinvestigated. Unlike previously reported, THTAA is a thermally stable compound that can be re-sublimed at 300–310 °C without decomposition. Controlled introduction of substituents at the nitrogen atoms of THTAA led to variation of its electron donor/acceptor capability that allowed fine-tuning the absorption properties. The propensity of these compounds and a number of its derivatives to form infinite chains involving >N–H···N= and >N–H···Hal−···N+ atoms is demonstrated by X-ray structure analysis. The DFT level optimized and experimental geometry of THTAA and its derivatives show considerable loss of aromaticity within the quinoxaline moiety.

Transformation of Nonporous Adaptive Pillar[4]arene[1]quinone Crystals into Fluorescent Crystals via Multi-Step Solid–Vapor Postsynthetic Modification for Fluorescence Turn-on Sensing of Ethylenediamine

“…In addition to monoamines, previous investigations showed that 1,4-benzoquinone (BQ) undergoes ring-formation reactions with EDA or 1,2-phenylenediamine to generate fluorescent compounds in the solution phase. − Therefore, we wondered whether fluorescent crystals could be genenerated by PSM of volatile EDA with the crystals of BQ or M1 in the solid–vapor phase. After exposure to EDA vapor, BQ crystals became viscous and their solubility decreased significantly.…”

“…Compared with the structures of M1 and M2 , M3 and M5 have neither benzoquinone subunit nor the subunit in which EDA is attached to benzoquinone. However, M3 and M5 have two similarities: (1) the benzoquinone subunits became conjugated planar quinoxaline moieties, which act as a fluorophore, − and (2) both X-ray crystal structures possess triclinic unit cells with a slipped-stacking arrangement (Table S2).…”