Photoalignment and surface-relief-grating formation are efficiently combined in low-molecular-weight halogen-bonded complexes.

Priimagi A, Saccone M, Cavallo G, Shishido A, Pilati T, Metrangolo P, Resnati G.

Adv Mater. 2012 Nov 20;24(44):OP345-52.

 

Collaborative work between the following Laboratories:

1. Chemical Resources Laboratory, Tokyo Institute of Technology, R1-12 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
2. Department of Applied Physics, Aalto University, School of Science and Technology, P.O. Box 13500, FI-00076 Aalto, Finland
3. NFMLab, DCMIC “Giulio Natta”, Politecnico di Milano, Via Mancinelli 7, I-20131 Milano, Italy
4. Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, Via Pascoli 70/3, I-20133 Milano, Italy
5. VTT – Technical Research Centre of Finland, Tietotie 2, FIN-02044 VTT, Finland

Abstract

It is demonstrated that halogen bonding can be used to construct low-molecular-weight supramolecular complexes with unique light-responsive properties. In particular, halogen bonding drives the formation of a photoresponsive liquid-crystalline complex between a non-mesogenic halogen bond-donor molecule incorporating an azo group, and a non-mesogenic alkoxystilbazole moiety, acting as a halogen bond-acceptor. Upon irradiation with polarized light, the complex exhibits a high degree of photoinduced anisotropy (order parameter of molecular alignment > 0.5). Moreover, efficient photoinduced surface-relief-grating (SRG) formation occurs upon irradiation with a light interference pattern, with a surface-modulation depth 2.4 times the initial film thickness. This is the first report on a halogen-bonded photoresponsive low-molecular-weight complex, which furthermore combines a high degree of photoalignment and extremely efficient SRG formation in a unique way. This study highlights the potential of halogen bonding as a new tool for the rational design of high-performance photoresponsive suprastructures.

Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

 

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Additional Information

Halogen bond is a rather exotic noncovalent interaction in the construction of supramolecular self-assemblies. It is said to be similar to the more familiar hydrogen bond, nevertheless it is the differences between these two interactions that open up new avenues for the design of innovative halogen-bond-based photoresponsive materials. Now, for the first time, researchers from Finland, Italy, and Japan have designed photoresponsive, halogen-bond-driven, liquid crystals. As reported in Advanced Materials ( DOI: 10.1002/adma.201204060), their material not only undergoes efficient photoalignment upon irradiation with polarized light, but more strikingly, thin films of the complex form surface-relief patterns with modulation depth exceeding the initial film thickness by a factor of 2.4 when irradiated with light interference pattern. The unique combination of efficient photoalignment and unprecedented mass-transport efficiency pinpoints halogen bonding as a new design tool for light-triggered, switchable supramolecular structures, with potential applications as, e.g., photocontrollable surfaces (for liquid-crystal alignment or non-wettability surfaces), and novel holographic-storage media.

Correspondence: [email protected]