Front Cover: Intense Molar Circular Dichroism in Fully Conjugated All‐Carbon Macrocyclic 1,3‐Butadiyne Linked pseudo‐meta [2.2]Paracyclophanes (Chem. Eur. J. 53/2022)

Abstract

Unprecedented high molar circular dichroism values for all‐carbon macrocycles were revealed in 1,3‐butadiyne bridged pseudo‐meta‐[2.2]paracyclophanes. The angle and flexibility of the pseudo‐meta substituents enabled high yielding macrocyclization reactions, and the studied trimeric, tetrameric, pentameric and hexameric structures further displayed astonishing through‐space polymer‐like conjugation lengths. More information can be found in the Research Article by M. Mayor et al. (DOI: 10.1002/chem.202201764).

Circularly Polarized Luminescence of Thiophene‐Bridged Macrocyclic pseudo‐meta [2.2]Paracyclophanes

“…[a] Values are reprinted from literature. [8] and are reported in Figure 4c. A constant g lum value of 0.003 with an unexpected sign inversion at 370 nm was observed for both enantiomers of the (R p ) n -2 n library.…”

“…[2] Especially the four pseudo disubstitution patterns [5] have caught the attention of molecular engineers due to their different geometries and in some cases even inherent chirality. Three of the pseudo-substituted PCP units, namely pseudo-ortho, [6,7] pseudo-meta [8,9] and pseudopara, [10] were recently embedded in macrocyclic structures, equipping the respective molecules with exemplary chiropticsa highly sought after property in optoelectronic materials. Besides different geometries, the PCP substitution patterns also display substantial differences in the electronic structure and electronic coupling through the 3D building block.…”

“…This led us to our recent work of thoroughly conjugated macrocycles incorporating several pseudo-meta PCPs interlinked by 1,3-butadiyne units. [8] The reported library (R p ) n -2 n , where n represents the number of PCP subunits (Figure 1a), displayed unprecedented circular dichroism (CD) intensities and was synthetically accessible in high yields thanks to the predefined angle of the pseudo-meta PCP subunit. The large absorption dissymmetry factors g abs (where g abs = Δɛ/ɛ) of 0.021 for (R p ) 4 -2 4 now urged the investigation of their circularly polarized luminescence (CPL) properties, particularly given the recently reported correlation of j g lum j = 0.94× j g abs j for planar chiral cyclophanes [12] (where g lum = 2(I L À I R )/(I L + I R ) and I is the CPL intensity).…”

“…For pseudo ‐meta PCPs constructive quantum interference was hypothesized theoretically [11] and corroborated experimentally, [4] suggesting the building block to be a valuable subunit for conjugated materials. This led us to our recent work of thoroughly conjugated macrocycles incorporating several pseudo‐ meta PCPs interlinked by 1,3‐butadiyne units [8] . The reported library ( R p ) n ‐ 2 n , where n represents the number of PCP subunits (Figure 1a), displayed unprecedented circular dichroism (CD) intensities and was synthetically accessible in high yields thanks to the predefined angle of the pseudo ‐meta PCP subunit.…”

Lemniscular carbon nanohoops with contiguous conjugation from planar chiral [2.2]paracyclophane: influence of the regioselective synthesis on topological chirality

“…To this end, 4,7,12,15-tetrasubstituted [2.2]paracyclophane (PCP) is considered as a promising chiral 3D candidate because its diverse substituent positions and unique planar chirality 11 allow us to fulfill regioselective synthesis and to control the topological chirality of targeted nanohoops. However, none of the PCP-based macrocycles reported so far dealt with topological chirality, 12 including our previously reported semi-macrocycles PCP-[n]CPP , 12 e which are also topologically trivial ( vide infra , Fig. S2†).…”