RESUMEN
Azacalixquinarenes, a new family of macrocycles composed of diaminobenzoquinone diimine units linked by dinitrobenzene rings, are synthesized by selective oxidation of the parent azacalixarenes. Crystallographic analyses of two compounds demonstrated the presence of canonical (uncharged) and zwitterionic quinones within a single structure. The electron-withdrawing nature of the dinitrobenzene moieties can trigger the intramolecular H-transfer that generates zwitterionic ground-state quinones. The nature of the N-substituents and the polarity of the solvent have a crucial impact on the equilibrium between the canonical and zwitterionic forms that present distinct optical and electrochemical properties. Thus, within [4]- and [6]-membered macrocycles, poly-zwitterionic structures can be reached, as demonstrated experimentally and theoretically using first-principle approaches.
RESUMEN
The fusion of two azacalixphyrin cycles absorbing in the NIR-I domain moves the absorption properties beyond 1000 nm, towards the second biological transparency window (NIR-II). This new type of NIR-II dye was synthesised through the intermediate preparation of a rare example of bis-tetra-azacalix[4]arene where the two macrocycles share a common aromatic unit.
RESUMEN
Near-infrared (NIR) azacalixphyrins bearing aryl substituents strongly impacting the physico-chemical properties of the macrocycles were designed, enabling hyperchromic and bathochromic shifts of the absorption compared to their N-alkylated analogues. This engineering enhances the photoacoustic response under NIR excitation, making azacalixphyrins promising organic contrast agents that reach the 800-1000 nm range.
RESUMEN
We describe the first isolation of N,N'-disubstituted benzoquinonediimines (QDIs) 2 which revealed drastically different properties compared to N,N',N'',N'''-tetrasubstituted QDIs 1 due to the absence of N-substituents in the "upper part" of the molecule. Three major differences could be highlighted thanks to the present joint experimental and theoretical investigation: (1) the metalation with different metal precursors revealed a specific behaviour in coordination chemistry giving access to novel complexes with unprecedented stoichiometry and remarkable absorption properties. More specifically, a new monoplatinum complex that is able to absorb light from the UV up to the NIR region because of its unique delocalization pathway across the metal centre was obtained; (2) this new class of di-substituted QDIs showed an exceptionally broad pKa range (ΔpKaâ¼ 8) that could be explained by the possible tuning of the basicity of each imine which is now attainable; (3) these quinones could be used as reagents in organic synthesis to form the previously unknown N,N',N'',N'''-tetrasubstituted QDIs with tuneable substituents (aryl vs. alkyl), previously unknown, as a new ligand for coordination chemistry.