Multi‐Color Photoluminescence Based on Mechanically and Thermally Induced Liquid‐Crystalline Phase Transitions of a Hydrogen‐Bonded Benzodithiophene Derivative

Abstract

Controlling assembled structures of π‐conjugated liquid‐crystalline molecules is of great interest in the development of stimuli‐responsive luminescent materials due to their molecular motility in the ordered states. Herein, we describe a mechanoresponsive hydrogen‐bonded benzodithiophene liquid‐crystalline molecule that exhibits a tricolor photoluminescence switching at ambient temperature. The compound shows a shear‐induced phase transition from a rectangular columnar to a metastable optically anisotropic mesophase, which is accompanied by the luminescent color change from yellow to sky‐blue. The metastable mesophase exhibits a time‐responsive transformation to another metastable mesophase showing a blue‐green emission through isothermal aging at room temperature. The luminescent color of aged sample reverts back to the initial yellow color by thermal annealing at 150 °C. These dynamic structural changes accompanied by the emission color changes are governed by distinct π‐stacking modes and hydrogen‐bonded patterns. The shear‐induced luminescent color change from yellow to blue is found to occur above the shear strain of 390 % at which the shear stress is 2.4×105 Pa as determined from dynamic viscoelastic measurements.

Unveiling the Role of Hydrogen Bonds in Luminescent N‐Annulated Perylene Liquid Crystals

“…No significant color changes were observed by application of mechanical force (shearing). [ 4 , 8 , 16 ] However, the thin films of 1 and 2 exhibited the reversible emission change upon exposure to vapors of organic solvents such as CHCl 3 , THF, hexane or toluene (Figures 4 c and S17–S19),[ 17 , 18 ] while thin films of 3 and 4 showed no significant changes (Figures S20 and S21). In particular, the thin film of 2 shows (under exposure to 365 nm light) an enhancement of the emission and a concomitant color change from yellow to green when exposed to CHCl 3 vapors (Figure 4 c).…”

Blue-Shifting Mechanofluorochromic Luminescent Behavior of Polymer Composite Films Using Gelable Mechanoresponsive Compound

“…In the case of LCs, anisotropy and aggregation structures can be easily controlled by external stimuli. By combining these properties with the functions of MCL, it is possible to develop special MCL materials that exhibit multicolor emission [12][13][14], circularly polarized PL [15], and anisotropy. Previously, we studied MCL materials based on liquid crystalline cyanostilbenes and detected the grinding direction using the stress orientation of LCs [16,17] and emission color control using supramolecular LC complexes [18,19].…”

Smart Supramolecular Self-Assembled Nanosystem: Stimulus-Responsive Hydrogen-Bonded Liquid Crystals

“…Once shear force was applied, these phase changes appeared. Similarly, another shear-responsive LC film using benzodithiophene molecules was reported [136]. At an applied shear press of 2.4 × 10 5 Pa (shear strain: 390%), this film showed a luminescent color change from yellow to sky blue, due to a phase transition from a rectangular columnar to a metastable optically anisotropic mesophase.…”