Synthesis of Asymmetric Coupled Polymethines Based on a 7-Chloropyrido[1,2-a]benzimidazole-8,9-dione Core

Abstract

A synthesis of 7-chloropyrido[1,2-a]benzimidazole-8,9-dione derivatives bearing fragments of widely used acceptor units has been performed, and their structures were investigated using the principle of coupled polymethines. Their electronic and electrochemical properties have also been studied. Compounds were isolated in both salt and neutral forms and depending on the introduced substituent can exist as o-quinone or p-quinone methide.

Studies of the Functionalized α-Hydroxy-p-Quinone Imine Derivatives Stabilized by Intramolecular Hydrogen Bond

“…It can be obtained in one-step synthesis from commercially available tetrachloro-1,4benzoquinone and 2-aminopyridine [17]. During earlier studies [17][18][19], it was proved that quinone 1a and some of its derivatives are electrochemically active compounds. Investigation of the reactivity of heterocyclic quinones 1 with Cand N-nucleophiles (primary amines) indicated that the attack of the nucleophile proceeds selectively at the C(6)-position of quinone.…”

Investigation of Weak Noncovalent Interactions Directed by the Amino Substituent of Pyrido- and Pyrimido-[1,2-a]benzimidazole-8,9-diones

“…Calculations proved the partial double-bond character of the C(6)–N(11) bond (Table S3). It is known that derivatives of 1a tend to form compounds that can be characterized as coupled polymethines . The partially charged merocyanine fragment can facilitate the formation of the resonance-assisted hydrogen bond …”

“…It is known that derivatives of 1a tend to form compounds that can be characterized as coupled polymethines. 23 The partially charged merocyanine fragment can facilitate the formation of the resonance-assisted hydrogen bond. 35 Analysis of X-ray data showed that the achiral compound 3c crystallized into a noncentrosymmetric chiral crystal that contains only (+) synclinal conformers (Figure 2a-1).…”

“…Imidazo[1,2-a]pyridine derivatives tend to form intramolecular H-bonds between the substituent and nitrogen of the heterocycle. 22 It was observed that derivatives of pyrido-and pyrimido[1,2a]benzimidazole-8,9-dione (Scheme 1a) possessing an electron-withdrawing group at the C(6) position can form Hbonded dimers 23 as well as π−π stacking interactions in the solid state. 24 ■ RESULTS AND DISCUSSION Synthesis.…”

Insights into extended coupled polymethines through the investigation of dual UV-to-NIR acidochromic switches based on heptamethine–oxonol dyes

“…[27][28][29][30] Furthermore, strong bathochromic shis were also found in simple diaminobenzoquinone monoimine derivatives (BQMI), which are highly stable ground-state zwitterions that can be viewed as an assembly of cyanine and oxonol trimethines Cy3 and Ox3. 31,32 To date, reports of new coupled polymethines (CoPo) remain scarce and usually arise from the serendipitous discoveries of original zwitterions, dianions or dications with moderately intense far-red to NIR absorption, as exemplied by the previously reported oxonol-containing bis-indene, 33 the coupled barbiturate-merocyanine, 34 the 7-chloropyrido[1,2-a] benzimidazole-8,9-dione core, 35 or the recently isolated dicationic pyrazine-linked bis-trimethine absorbing beyond 800 nm. 36 These rare examples highlight that the coupling principle appears as an unexplored strategy to design unique NIR dyes, and that structure-property relationships are still to be unravelled to amplify both the absorption as well as the emission properties of the resulting compounds in a way to open up new spectroscopic and applicative horizons.…”