Towards Photocontrol over the Helix–Coil Transition in Foldamers: Synthesis and Photoresponsive Behavior of Azobenzene‐Core Amphiphilic Oligo(meta‐phenylene ethynylene)s

Abstract

Introduction of photochromic azobenzene units into amphiphilic oligo(meta-phenylene ethynylene)s allowed photocontrol over the helix-coil transition in this important class of foldamers. Two design principles were followed in efforts to accommodate cis- and trans-azobenzene moieties within the helical structure to selectively turn the helical state on and off, respectively. Several oligomer series with varying connectivities to the central azobenzene chromophore were synthesized and these photochromic oligomers were investigated with regard to their folding behavior in both dark and irradiated states. Both the foldamers' chain lengths and the electronic structures of the azobenzene moieties had to be optimized to ensure folding differences and selective excitation of the photochrome. The design of such stimuli-responsive macromolecules, displaying large structural changes upon irradiation, should guide the design of future materials in, for example, "smart" delivery applications.

Synthesis and self-assembly of fluorene-vinylene alternating copolymers in “Hairy-Rod” architecture: side chain – mediated tuning of conformation, microstructure and photophysical properties

“…as copolymer 12 is amphiphilic in nature, the driving force for such folding behavior could be the solvophobicity of the non-polar aromatic backbone in polar environment, resulting in an intramolecular segregation, analogous to nanophase separation usually encountered in amphiphilic block-copolymers. [68] 1 H-nMr, UV-vis and fluorescence spectroscopy, and aFM microscopic results corroborate the assumption that the folding was induced most probably by intramolecular π-π stacking between non-adjacent moieties in the backbone and their solvophobic interactions and that, the helical geometry was encoded in the backbone topology as well as in its constitutive parts.…”

Recent advances in arylene ethynylene folding systems: Toward functioning

“…Hecht et al reported the photoswitchable foldamers 55-57 by harnessing the photoisomerizable azobenzene unit [109,110].…”

Azobenzenes—synthesis and carbohydrate applications

“…Hecht et al reported the synthesis of azobenzene-core amphiphilic oligo(meta-phenylene ethynylene)s. 32 After bromination of methyl 3-nitrobenzoate (39), treatment of 40 with zinc under basic conditions yielded the desired azobenzene bis-acid 41 in 63% yield (two steps) (Scheme 16).…”