Halogen Bonding versus Hydrogen Bonding in Driving Self‐Assembly and Performance of Light‐Responsive Supramolecular Polymers

Abstract

Halogen bonding is arguably the least exploited among the many non-covalent interactions used in dictating molecular self-assembly. However, its directionality renders it unique compared to ubiquitous hydrogen bonding. Here, the role of this directionality in controlling the performance of light-responsive supramolecular polymers is highlighted. In particular, it is shown that light-induced surface patterning, a unique phenomenon occurring in azobenzene-containing polymers, is more efficient in halogen-bonded polymer–azobenzene complexes than in the analogous hydrogen-bonded complexes. A systematic study is performed on a series of azo dyes containing different halogen or hydrogen bonding donor moieties, complexed to poly(4-vinylpyridine) backbone. Through single-atom substitution of the bond-donor, control of both the strength and the nature of the noncovalent interaction between the azobenzene units and the polymer backbone is achieved. Importantly, such substitution does not significantly alter the electronic properties of the azobenzene units, hence providing us with unique tools in studying the structure–performance relationships in the light-induced surface deformation process. The results represent the first demonstration of light-responsive halogen-bonded polymer systems and also highlight the remarkable potential of halogen bonding in fundamental studies of photoresponsive azobenzene-containing polymers

Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

“…14a, allows for tuning the halogen bonding interaction strength with pyridine. 144,145 As Fig. 14b and c show, there is a direct correlation with the halogen bond strength and SRG formation efficiency, the iodine-capped (resulting in relatively strong halogen bonding) azobenzene complexed with P4VP resulting in the highest and fluorinecapped (no specific interaction with P4VP) resulting in the lowest SRGs.…”

“…Moreover, it was shown that in the concentration range studied (10-20 mol%), the halogen-bonded polymerazobenzene complexes outperform the corresponding hydrogenbonded analogues in SRG formation efficiency, even though the hydrogen bond interaction is significantly stronger. 144,145 This was attributed to the higher directionality of the halogen bond compared to hydrogen bond. Thus, both the nature and strength of the supramolecular bond make a significant difference in the SRG formation efficiency.…”

Facile synthesis and characterizations of copper–zinc-10,15,20-tetra(4-pyridyl) porphyrin (Cu–ZnTPyP) coordination polymer with hexagonal micro-lump and micro-prism morphologies

“…As their microstructures can be deliberately and easily modified, the ICPs have gained growing attention in potential applications such as gas storage [3] and separation [4], drug delivery [5], and catalysis [6]. The formation of various ICPs morphologies mainly depends on the intra-molecules non-covalent interactions such as metal-ligand interactions [7]，hydrogen bonding [8] and π-π stacking [9]. In comparison with metal organic frameworks (MOFs), these ICPs exhibit a higher level of structural tailorability, including size and morphology-dependent properties.…”

Coordination networks incorporating halogen-bond donor sites and azobenzene groups

“…This contact is quite short especially if compared to the only other XB found in the CSD involving an iodine atom and an azo group (Refcode: TEGFUI; 3.240 Å (N c = 0.95), 152.5°). 29 This short contact is rather unexpected as nitrogen atoms of the azo moiety are only mildly basic and thus poor XB-acceptors. 30 Probably, the tight proximity imposed by the network conveniently preorganizes the interacting units and favors the occurrence of a relatively short XB.…”