Stereocontrolled Synthesis of Chiral Heteroaromatic Propellers with Small Optical Bandgaps

Abstract

Chiral heteroaromatic propellers based on radially p-extended hexapyrrolohexaazacoronenes were obtained in ac oncise synthesis from suitably functionalizedd onoracceptor monopyrroles.T oo vercome steric hindrance,anew cyclodehydrogenation method was developed, and it uses bromine electrophiles as oxidative coupling agents instead of the commonly employed high-potential oxidants.T he new reaction offers high yields of propeller-shaped targets,even for electron-deficient precursors,a nd shows electrophile-dependent stereoselectivity,w ith N-bromosuccinimide and dibromine yielding,r espectively D 6 -a nd C 2 -symmetric products. The propeller azacoronenes are chiral and can be separated into configurationally stable enantiomers.I na ddition to providing steric bulk, peripheral functionalization considerably affects the electronic properties of the propellers,w hich exhibit reduced optical and electrochemical band gaps,a nd amore clearly defined electroreduction behavior.

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…It is also worth emphasizing that some very strained products, such as helicenes, bowls and saddles, can be synthesized using this method. Indeed, in contrast to earlier assumptions, the Scholl reaction is capable of proceeding even if ring closure is accompanied by the introduction of significant steric strain that leads to nonplanar molecules . Progress has been particularly impressive in the case of surface‐assisted dehydrogenation, which has enabled the synthesis of nanographenes of unprecedented size by scanning tunneling microscopy …”

“…Indeed, in contrast to earlier assumptions,the Scholl reaction is capable of proceeding even if ring closure is accompanied by the introduction of significant steric strain that leads to nonplanar molecules. [274,275] Progress has been particularly impressive in the case of surface-assisted dehydrogenation, which has enabled the synthesis of nanographenes of unprecedented size by scanning tunneling microscopy. [169,276] Despite all the impressive progress summarized herein, methods for the oxidative coupling of arenes still have some limitations,which will no doubt be the focus of future studies.…”

Chiroptical Symmetry Analysis of Trianglimines: A Case Study

“…As illustrated in Figure 2, R 12 is the distance between origins of the ETDMs of two chromophores, θ is the angle between EDTM and C 3 -axis (z-axis) and ω is the angle between the projection of EDTM for chromophores on the xy plane with the x-axis (for D 3 symmetry, the required angle is 90 • ). V 12 value is obtained as indicated [3]. The module of the EDTM obtained by TD-DFT for the monomer is 2.54 au.…”

“…An object is chiral when it is non-superimposable with its mirror-image [1]. Examples presenting this property vary from macroscopic such as screws or spiral staircases to microscopic i.e., nanoparticles [2] and molecules [3] among others. Furthermore, two chiral mirror-image molecules are called enantiomers.…”

Porphyrin‐Ryleneimide Hybrids: Low‐Bandgap Acceptors in Energy‐Transfer Cassettes

“…[11,13] Here we demonstrate the utility of ryleneimide-metalloporphyrin hybrids as acceptor units in energy transfer cassettes ( Figure 1). The parent chromophore, [14] containing four naphthalenemonoimide (NMI) units fused to a central porphyrin moiety, belongs to a recently developed family of donoracceptor (DA) oligopyrroles, [15][16][17][18][19] characterized by small electronic bandgaps, and extended redox activity. Related DA porphyrins have recently been explored as agents for antimicrobial photodynamic inactivation of Gram-positive bacteria.…”