Title: Red-light-Controllable Liquid-Crystal Soft Actuators via Low-power Excited Upconversion Based on Triplet-Triplet Annihilation

Author: Zhen Jiang , Ming Xu , Fuyou Li*, Yanlei Yu*

Journal: J. Am. Chem. Soc., 2013, 135(44), 16446-16453

Abstract:

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 trans–cis 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.

Fulltext Link: https://pubs.acs.org/doi/abs/10.1021/ja406020r

In this work, the strategy of utilizing the TTA-UCL technology as the low-power excited, long-wavelength phototrigger of the light-sensitive CLCP has been demonstrated. Initially, we achieved a highly effective red-to-blue TTA-based upconversion system with low-energy excitation light source and a high absolute quantum yield of 9.3 ± 0.5%. To employ it as the phototrigger of the azotolane CLCP, this TTA-UCL system was incorporated into a rubbery polyurethane film and then assembled with azotolane CLCP film. The generating assembly film bent toward the light source when irradiated with a 635 nm laser at low power density because the TTA-UCL was effectively utilized by the azotolane moieties in the CLCP film, inducing their trans−cis photoisomerization and an alignment change of the mesogens via an emission−reabsorption process. 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.