Helical Ullazine‐Quinoxaline‐Based Polycyclic Aromatic Hydrocarbons. Issue 5 (21st December 2018)

• Record Type: Journal Article
• Authors: Richter, Marcus; Hahn, Sebastian; Dmitrieva, Evgenia; Rominger, Frank; Popov, Alexey; Bunz, Uwe H. F.; Feng, Xinliang; Berger, Reinhard
• Is Part Of: Chemistry. Volume 25:Issue 5(2019)
• Page Start: 1345
• Page End: 1352
• Publication Date: 2018-12-21
• Subjects: azaacene -- cycloaddition -- helical structures -- heterocycles -- polycyclic aromatic hydrocarbons; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201804751
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Polycyclic aromatic azomethine ylides (PAMYs) are powerful building blocks in the bottom‐up synthesis of internally nitrogen‐containing polycyclic aromatic hydrocarbons (N‐PAHs) through 1, 3‐cycloaddition reactions. In this work, the cycloaddition reaction of PAMYs to asymmetric ortho ‐quinones is presented, which, in contrast to the addition to symmetric para ‐quinones, facilitates subsequent condensation reactions and allows the synthesis of three helical N‐PAHs with ullazine‐quinoxaline (UQ ‐1 –3 ) backbones.UQ ‐1 andUQ ‐2 possess two helical centers; however, single‐crystal X‐ray analysis together with the computational modeling ofUQ ‐3 elucidate the formation of only the thermodynamically most stable geometry with four helical centers in a ( P, P, M, M ) configuration. For the seriesUQ ‐1 –3, the number of redox steps is directly correlated with the number of ullazine or quinoxaline units incorporated into the targeted molecular backbones. A detailed investigation of the spectroscopic and magnetic properties of the radical cation and anion as well as the dication and dianion species by in situ EPR/UV/Vis‐NIR spectroelectrochemistry is provided. The excellent optical and redox properties combined with helical geometries render them possibly applicable as chiral emitter or ambipolar charge transport material in organic electronics. Abstract : Polycyclic aromatic hydrocarbons (PAHs) with ullazine‐quinoxaline (UQ) backbones have been synthesized by 1, 3‐cycloadditions of polycyclic aromatic azomethine ylides (PAMYs) to ortho ‐quinones and subsequent condensation reactions (see Scheme). The properties of the UQs were investigated by single‐crystal X‐ray analysis, UV/Vis absorption spectroscopy, cyclic voltammetry and computational modeling. Furthermore, radical species of UQs were obtained by EPR/UV‐Vis‐NIR spectroelectrochemistry.