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Red-Light-Controllable Liquid-Crystal Soft Actuators via Low-Power Excited Upconversion Based on Triplet–Triplet Annihilation

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posted on 06.11.2013 by Zhen Jiang, Ming Xu, Fuyou Li, Yanlei Yu
A red-light-controllable soft actuator has been achieved, driven by low-power excited triplet–triplet annihilation-based upconversion luminescence (TTA-UCL). First, a red-to-blue TTA-based upconversion system with a high absolute quantum yield of 9.3 ± 0.5% was prepared by utilizing platinum­(II) tetra­phenyl­tetra­benzo­porphyrin (PtTPBP) as the sensitizer and 9,10-bis­(di­phenyl­phosphoryl)­anthracene (BDPPA) as the annihilator. In order to be employed as a highly effective phototrigger of photodeformable cross-linked liquid-crystal polymers (CLCPs), the PtTPBP&BDPPA system was incorporated into a rubbery polyurethane film and then assembled with an azotolane-containing CLCP film. The generating assembly film bent toward the light source when irradiated with a 635 nm laser at low power density of 200 mW cm–2 because the TTA-UCL was effectively utilized by the azotolane moieties in the CLCP film, inducing their transcis photo­isomerization and an alignment change of the mesogens via an emission–reabsorption process. It is the first example of a soft actuator in which the TTA-UCL is trapped and utilized to create photomechanical effect. Such advantages of using this novel red-light-controllable soft actuator in potential biological applications have also been demonstrated as negligible thermal effect and its excellent penetration ability into tissues. This work not only provides a novel photo­manipulated soft actuation material system based on the TTA-UCL technology but also introduces a new technological application of the TTA-based upconversion system in photonic devices.

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