Supramolecular hierarchy among halogen and hydrogen bond donors in light-induced surface patterning

Abstract

Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an iodoethynyl-containing azobenzene comes out on top of the supramolecular hierarchy to provide unprecedented photoinduced surface patterning efficiency. Specifically, the iodoethynyl motif seems highly promising in future development of polymeric optical and photoactive materials driven by halogen bonding

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.…”

Light-Triggered Formation of Surface Topographies in Azo Polymers

“…Surprisingly, they reported that for their hydrogen bonded polymer (P4VP-OH(DMA)), only 1 mol % of chromophore loading was sufficient to obtain efficient gratings ( Figure 5a); hence, the inscription rate is lowered by decreasing chromophore concentration. In addition to the use of hydrogen bonds to create supramolecular azobenzene-containing polymers, Priimagi and co-workers reported on the creation of supramolecular polymers by use of halogen bonds [78][79][80][81]. They determined the superiority of halogen-bonded polymer-azobenzene complexes over the analogous hydrogen-bonded complexes.…”

“…Recently, a more comparative study of different halogen bond donor chromophores showed that the efficiency of the SRG formation is increased with interaction strength (Figure 6). Moreover, the most effective halogen bond donor was found to be a iodoacetylene azo dye [81]. Seki et al reported on liquid crystalline linear polymer systems that can create SRGs with light [38,82,83].…”

“…In turn, this leads to the partial or complete erasure of the SRGs. This light-initiated erasure of the gratings is more appealing than thermal erasure due to its capability of generating "on" and "off" states that can be controlled remotely, affect the film [81]. The label X can be either H, OH, or any halogen.…”

“…(f) Diffraction efficiency of the different fluorinated and (g) AFM surface profiles of the gratings for azobenzene modules P4VP(n) 0.1 (a) with n = 1 (X = F), n = 2 (X = Br) and n = 3 (X = I). Reproduced from [81].…”