Tetraphenylhexaazaanthracenes: 16π Weakly Antiaromatic Species with Singlet Ground States

Abstract

Tetraphenylhexaazaanthracene, TPHA-1, is a fluorescent zwitterionic biscyanine with a closed-shell singlet ground state. TPHA-1 overcomes its weak 16π antiaromaticity by partitioning its π system into 6π positive and 10π negative cyanines. The synthesis of TPHA-1 is low yielding and accompanied by two analogous TPHA isomers: the deep red, non-charge-separated, quinoidal TPHA-2, and the deep green TPHA-3 that partitions into two equal but oppositely charged 8π cyanines. The three TPHA isomers are compared.

Thermally and Magnetically Robust Triplet Ground State Diradical

“…21 Cyano-Blatter radical 3 is synthesized by adopting procedures available in the literature, as outlined in detail in the Supporting Information. 17,[22][23][24][25] Treatment of 3 with DIBAL-H followed by hydrolysis of the imine group provides formyl-Blatter radical 4. Radical 4 is initially reduced to the corresponding leuco-amine-aldehyde, or alternatively, it is directly condensed with 2,3bis(hydroxyamino)-2,3-dimethylbutane; 26 the resultant adduct is oxidized in air to provide diradical 2, which is purified by normal phase chromatography (silica gel) at ambient conditions.…”

An Unprecedented Blue Chromophore Found in Nature using a “Chemistry First” and Molecular Networking Approach: Discovery of Dactylocyanines A–H

“…The consequences of the presence of two delocalized π‐systems are reflected by the physical properties . Measurements of the optical properties of 3 and 4 , indicate a significant sensitivity to the solvent polarity and a typical negative solvatochromism (Figure ). In comparison, ilimaquinone ( 1 ) shows a moderate positive solvatochromism with a greater sensitivity to the pH.…”

N1-(5-Fluoro-2,4-dinitrophenyl)-N2-phenyl-4-(trifluoromethyl)benzene-1,2-diamine

“…Disappointingly, after 4 h, we obtained a mixture of N 1 -(5-ethoxy-2,4-dinitrophenyl)-N 2 -phenyl-4-(trifluoromethyl)benzene-1,2-diamine (5) (38%) and the desired N 1 -(5-fluoro-2,4-dinitrophenyl)-N 2 -phenyl-4-(trifluoromethyl)benzene-1,2-diamine (6) (51%) which required chromatographic separation (n-hexane/DCM) (Scheme 2). Our interest in difluorodinitrobenzene 1 stems from its use as a starting point in the synthesis of biscyanine azaacenes such as the hexaazaanthracene 2 [20,21] and the tetraazapentacene 3 [22][23][24][25] ( Figure 1) that followed a modification of Nietzki's classical preparation of tetraazapentacene from 1,2-diaminobenzenes and the considerably less reactive 1,5-dichloro-2,4-dinitrobenzene [26]. A key initial step in preparing asymmetrically-substituted biscyanine tetraazaacene analogues [23] is the selective displacement of one fluorine by N 1 -aryl/alkyl 1,2-benzenediamines and this is typically achieved at 0-20 °C in solvents such as EtOH or MeOH in the presence of either triethylamine or pyridine (1 equiv) or additional N 1 -aryl/alkyl 1,2-benzenediamine (1 equiv).…”

“…Our interest in difluorodinitrobenzene 1 stems from its use as a starting point in the synthesis of biscyanine azaacenes such as the hexaazaanthracene 2 [20,21] and the tetraazapentacene 3 [22][23][24][25] ( Figure 1) that followed a modification of Nietzki's classical preparation of tetraazapentacene from 1,2-diaminobenzenes and the considerably less reactive 1,5-dichloro-2,4-dinitrobenzene [26].…”

“…General structure of biscyanines 2 and 3 prepared from difluorodinitrobenzene 1[20][21][22][23][24][25].…”