Verma Parul, Singh Ashish, Maji Tapas Kumar
Molecular Material Laboratory, Chemistry and Physics of Material Unit, School of Advanced Materials (SAMat), Jawaharlal Nehru Centre for Advanced Scientific Research Jakkur Bangalore-560064 India
Chem Sci. 2020 Dec 23;12(7):2674-2682. doi: 10.1039/d0sc05721e.
Photo-switching emission of photochromic materials has paramount importance in the field of optoelectronics. Here, we report synthesis and characterization of a dithienylethene (DTE) based photochromic low molecular weight gelator (LMWG) and self-assembly with lanthanide (Eu and Tb) ions to form a photochromic coordination polymer gel (pcCPG). Based on DTE ring opening and closing, the TPY-DTE gel shuttles from pale-yellow coloured TPY-DTE-O to dark blue coloured TPY-DTE-C and upon irradiating with UV and visible light, respectively, and both the photoisomers show distinct optical properties. Furthermore, integration of Eu and Tb lanthanides with TPY-DTE resulted in red and green emissive Eu-pcCPG (Q.Y. = 18.7% for the open state) and Tb-pcCPG (Q.Y. = 23.4% for the open state), respectively. The photoisomers of Eu-pcCPG exhibit photo-switchable spherical to fibrous reversible morphology transformation. Importantly, an excellent spectral overlap of the Eu centred emission and absorption of DTE in the closed form offered photo-switchable emission properties in Eu-pcCPG based on pcFRET (energy transfer efficiency >94%). Further, owing to the high processability and photo-switchable emission, the Eu-pcCPG has been utilized as invisible security ink for protecting confidential information. Interestingly, mixed Eu/Tb pcCPG exhibited photo-modulated multi-spectrum chromism reversibly where the colour changes from yellow, blue, and red to green and under suitable light irradiation.
光致变色材料的光开关发射在光电子学领域具有至关重要的意义。在此，我们报道了一种基于二噻吩乙烯（DTE）的光致变色低分子量凝胶剂（LMWG）的合成与表征，以及它与镧系元素（铕和铽）离子自组装形成光致变色配位聚合物凝胶（pcCPG）。基于DTE的开环和闭环，TPY-DTE凝胶分别在紫外光和可见光照射下，从浅黄色的TPY-DTE-O穿梭至深蓝色的TPY-DTE-C，并且两种光异构体都表现出独特的光学性质。此外，铕和铽镧系元素与TPY-DTE的整合分别产生了发红光和绿光的Eu-pcCPG（开态时量子产率 = 18.7%）和Tb-pcCPG（开态时量子产率 = 23.4%）。Eu-pcCPG的光异构体表现出可光开关的球形到纤维状的可逆形态转变。重要的是，基于pcFRET（能量转移效率>94%），Eu中心发射与闭环形式的DTE吸收之间的出色光谱重叠赋予了Eu-pcCPG光开关发射特性。此外，由于高加工性和光开关发射特性，Eu-pcCPG已被用作隐形安全墨水来保护机密信息。有趣的是，混合的Eu/Tb pcCPG在适当的光照射下可逆地表现出光调制多光谱变色，颜色从黄色、蓝色和红色变为绿色。
