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

• Published in: Chemphyschem Vol. 21; no. 4; pp. 328 - 334
• Main Authors: Seki, Atsushi, Yoshio, Masafumi
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 17.02.2020
• Subjects: Ambient temperature; benzodithiophene derivatives; Crystal structure; Crystallinity; Emission; Hydrogen; hydrogen bonds; liquid crystals; mechanochromic materials; Mesophase; Phase transitions; Photoluminescence; Room temperature; Shear strain; Shear stress; π-conjugated molecules; benzodithiophene derivatives; liquid crystals; hydrogen bonds; mechanochromic materials; π-conjugated molecules
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201901004

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. Colors for a change! A mechanofluorochromic benzodithiophene‐based liquid crystal exhibits the tricolor emissions due to the mechanically and thermally induced phase transitions is investigated. The mechanofluorochromic liquid crystals presents a good candidate for surface coating materials for tribological uses.