Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals

Abstract

Here, we present a new family of light-responsive, fluorinated supramolecular liquid crystals (LCs) showing efficient and reversible light-induced LC-to-isotropic phase transitions. Our materials design is based on fluorinated azobenzenes, where the fluorination serves to strengthen the noncovalent interaction with bond-accepting stilbazole molecules, and increase the lifetime of the cis-form of the azobenzene units. The halogen-bonded LCs were characterized by means of X-ray diffraction, hot-stage polarized optical microscopy, and differential scanning calorimetry. Simultaneous analysis of light-induced changes in birefringence, absorption, and optical scattering allowed us to estimate that <4% of the mesogenic units in the cis-form suffices to trigger the full LC-to-isotropic phase transition. We also report a light-induced and reversible crystal-to-isotropic phase transition, which has not been previously observed in supramolecular complexes. In addition to fundamental understanding of light-responsive supramolecular complexes, we foresee this study to be important in the development of bistable photonic devices and supramolecular actuators.

The Halogen Bond: An Emerging Supramolecular Tool in the Design of Functional Mesomorphic Materials

“…Photoinduced phase transitions have also been reported by the group of Priimagi in halogen‐bonded liquid‐crystalline materials (Scheme ) . The light‐driven phase transition process was found to be reversible and highly efficient.…”

“…Photoinduced phase transitions have also been reported by the group of Priimagi in halogen-bonded liquid-crystalline materials (Scheme 14). [84] The light-driven phase transition process was found to be reversible and highly efficient. Photomodulation of birefringence, opticals cattering and absorption were investigated in the photoresponsive halogen-bonded LCs to gain insighti nto the isothermal phase transition.…”

Identification of an Overlooked Halogen‐Bond Synthon and Its Application in Designing Fluorescent Materials

“…Its potential, however,a rises from its unique characteristics in terms of directionality,t unability,h ydrophobicity,a nd large donor-atom size. [2] As av ersatile design element, it enables the construction of novel supramolecular assemblies [3][4][5][6][7] andf inds application in designing multicomponent functional materials, such as liquid crystals [8,9] and nonlinearo ptical, [10,11] fluorescent, [12,13] and phosphorescent materials. [14][15][16] The quest for novel supramolecular synthons is akey activity in halogen-bond research.…”

Photo-Orientation Phenomena in Photochromic Liquid Crystalline Azobenzene-Containing Polymethacrylates with Different Spacer Length

“…[1][2][3][4] Photoisomerization of azobenzene fragments in LC media enables to realize isothermal phase transitions. [5][6][7][8][9][10][11][12] From the other hand, an action of polarized light induces photo-orientation processes and alignment of chromophores in direction perpendicular to the polarization plane of the incident light. [13][14][15][16][17][18][19][20] Another interesting direction of the research is connected with investigation of the surface topography of LC polymer systems and, especially, manipulation of surface relief by light irradiation.…”