Hydrogen‐Bonding‐Induced One‐Handed Helical Polynorbornenes Appended With Chiral Alaninegland

Abstract

Polynorbornenes appended with anthracene and chiral alanine linkers are synthesized. Hydrogen bonding between the adjacent bisamidic linkers brings adjacent anthracene chromophores in a more suitable orientation for exciton coupling and renders one-handed helical structures for these polymers. Excimer formation is observed from their emission spectra. Monoamidic linkers provide only one hydrogen bond, which would be less robust and result in much lower circular dichroic response.

Controlling the Orientation of Pendants in Two-Dimensional Comb-Like Polymers by Varying Stiffness of Polymeric Backbones

“…The porphyrin-appended norbornene and cyclobutene monomers 10 and 11 were prepared according to reported procedures. ,, ROMP of 10 and 11 in the presence of 3 afforded isotactic polynorbornene 8a (Z/ E = 18/82) and isotactic polycyclobutene 9a (Z/ E = 66/34), respectively. Z -Isotactic polynorbornene 8b ( Z / E = >99/<1) and Z -isotactic polycyclobutene 9c (Z/ E = 96/4) were obtained from 10 and 11 , respectively, by using Schrock–Hoveyda catalyst 4 .…”

“…Conformational disorder arising from rotatory single bonds may lead to irregular microstructures on the backbone. The control over the position of pendants in two-dimensions relies on the use of a more rigid scaffolds including oligoproline, nucleic acid, polyisocyanides and polynorbornenes. ,− Accordingly, interactions between pendant chromophores would be more efficient if they could be better aligned along polymeric backbone.…”

“…The spacing separating adjacent monomeric units for these polynorbornenes is about 5.5 Å . Interactions between neighboring pendants or linkers can be discerned by various spectroscopic means. − Fluorescence quenching, ,, excimer formation, Soret band splitting, ,, and enhancement of chiroptical properties ,, and second order optical nonlinearity are frequently observed in these polynorbornene-based polymers.…”

“…Thanks to the rapid development of various catalytic systems, − the stereochemistry of double bonds and the tacticity of polymers derived from the ROMP of strained cycloalkenes can be well controlled. Thus, double bonds in 1 are predominantly, if not exclusively, trans when the first generation Grubbs catalyst 3 is used, − whereas Z-selectivity is obtained when the Schrock–Hoveyda catalyst 4 − , is employed . More recently, cyclobutene derivatives 6 was transformed into polycyclobutenes 7 using 3 , 4 , or 5 as the catalyst (eq 2).…”

Excimer Formation in a Confined Space: Photophysics of Ladderphanes with Tetraarylethylene Linkers

“…[14d,e] The third possibility is the formation of an excited dimer, which may exhibit a new structureless emission at longer wavelength. [29] In particular, if the chromophores are in a confined space, such as anthracene appended in polynorbornene, [41] terphenylene-diethynylenelinked ladderphane, [14d] and surface attachment of pyrene on porous silica, [42] excimer emissions are observed. As mentioned above, neither TAE core 6 nor monomers 10 a and 10 b exhibit any emission at ambient temperature.…”