A Stimuli‐Responsive, Photoluminescent, Anthracene‐Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical Processes

Abstract

Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable–stable phase transition induced by external stimuli is prepared. A 2,6‐diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6‐diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid‐crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic‐columnar phase transition induced by heating or mechanical shearing for this 2,6‐diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable–stable LC phase transition.

Design amphiphilic dipolar π-systems for stimuli-responsive luminescent materials using metastable states

“…Recently, luminescent materials that are responsive to mechanical stimuli have attracted considerable attention because they have the unique ability to tune their molecular, physical or chemical properties via macroscopic stimulation [5][6][7][8] . Several mechanistic explanations for the mechanically stimulated changes in the colour of the luminescence have been proposed: a phase transformation of the solid structure [9][10][11][12][13][14][15][16] , excimer formation or dissolution [17][18][19] and mechanical stress-induced chemical changes 20,21 .…”

A Piezochromic Luminescent Complex: Mechanical Force Induced Patterning with a High Contrast Ratio

“…[2][3][4] The tuning of the luminescence of organic solids by mechanical forces has been realized through changing the chemical structures containing opened/closed cyclic forms [5] and double-bond E/Z configurations.[6] However, relatively high pressure is necessary to promote chemical reactions, [7] and poor reversibility has been considered as a drawback in such systems. In contrast, controlling the mode of molecular packing (aggregation states) is more attractive for both fundamental research and practical applications due to low pressure demand and good reversibility, but successful systems are quite limited.…”

Thermal or Mechanical Stimuli‐Induced Photoluminescence Color Change of a Molecular Assembly Composed of an Amphiphilic Anthracene Derivative in Water

“…In the case of a liquid-crystalline anthracene derivative with a similar molecular structure to 1, a peak due to free amide C=O groups was observed at around ñ = 1685 cm À1 . [13] Hydrogen bonds are retained after annealing (Figure 5 b). No peaks that correspond to amide NÀH stretching were observed because they were masked by the large and broad peaks ascribed to OÀH stretching of many hydroxy groups of 1.…”