Zhang Tingting, Wang Xuan, An Zhongfu, Fang Zhiwei, Zhang Yongming, Yuan Wang Zhang
School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, China.
Shanghai Key Lab of Electrical Insulation and Thermal Aging, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, China.
Chemphyschem. 2018 Sep 18;19(18):2389-2396. doi: 10.1002/cphc.201800310. Epub 2018 Jun 20.
Persistent room-temperature phosphorescence (p-RTP) of pure organic materials is attracting increasing attention. The design of efficient phosphors and understanding the origin of p-RTP, however, remain challenging. Herein, to gain further insights into pure organic p-RTP, we prepared a group of carbazole (CZ) and methyl benzoate (MBA) conjugates with a methyl ester unit at the para (4-MBACZ), meta (3-MBACZ), and ortho (2-MBACZ) sites. These isomers merely produce prompt fluorescence in solutions, but generate blue prompt/delayed fluorescence (DF) and orange p-RTP with lifetimes up to 865.2 ms in the crystalline state. Lifetimes of p-RTP are in the order of 2-MBACZ>3-MBACZ>4-MBACZ, which might be mainly ascribed to the combined effect of packing density, intermolecular interactions and steric hindrance. Meanwhile, upon mechanical grinding, while the emission color and profile of the luminogens do not significantly change, no (4-MBACZ) or shortened (3-MBACZ, 2-MBACZ) p-RTP is observed, accompanying the change from crystalline to amorphous states. Such p-RTP at amorphous states without external hosts is rarely reported, which demonstrates important implications for the molecular design and mechanism understanding towards p-RTP. Furthermore, their p-RTP attribute and different emission colors before and after ceasing the UV irradiation endow them promising applications in encryption and anticounterfeiting fields.
纯有机材料的持久室温磷光（p-RTP）正吸引着越来越多的关注。然而，高效磷光体的设计以及对p-RTP起源的理解仍然具有挑战性。在此，为了进一步深入了解纯有机p-RTP，我们制备了一组在对位（4-MBACZ）、间位（3-MBACZ）和邻位（2-MBACZ）带有甲酯单元的咔唑（CZ）和苯甲酸甲酯（MBA）共轭物。这些异构体在溶液中仅产生即时荧光，但在结晶态下产生蓝色即时/延迟荧光（DF）和橙色p-RTP，寿命长达865.2 ms。p-RTP的寿命顺序为2-MBACZ>3-MBACZ>4-MBACZ，这可能主要归因于堆积密度、分子间相互作用和空间位阻的综合影响。同时，在机械研磨时，虽然发光体的发射颜色和轮廓没有明显变化，但未观察到（4-MBACZ）的p-RTP或（3-MBACZ、2-MBACZ）的p-RTP缩短，同时伴随着从结晶态到非晶态的转变。这种无外部主体的非晶态下的p-RTP鲜有报道，这对p-RTP的分子设计和机理理解具有重要意义。此外，它们的p-RTP特性以及在停止紫外照射前后的不同发射颜色使其在加密和防伪领域具有广阔的应用前景。
