基于二氧化硅纳米颗粒的三重态-三重态湮灭上转换研究

Triplet-Triplet Annihilation Upconversion Based on Silica Nanoparticles

以氟化的四苯基卟啉铂为光敏剂,硅氧烷衍生化的9,10-二苯基蒽为发光体构筑了基于三重态-三重态湮灭机制的上转换体系.采用紫外可见分光光度计和荧光光谱仪研究了其在二氯甲烷溶液中的上转换性能,确定了光敏剂和发光体的最佳比例为1∶40.在此比例下,以胶束模板法构筑了尺寸均一,能在水中稳定的上转换二氧化硅纳米颗粒,通过透射电子显微镜(TEM)和动态光散射仪(DLS)表征了其形貌和尺寸(TEM统计平均直径为15.5nm,平均水合直径为22.5nm);当以532nm的激光作为激发光源时,实现了水中的上转换发射,上转换发光寿命为12μs,上转换量子效率为0.8%.

Photon upconversion based on triplet-triplet annihilation (TTA) composed of organic photosensitizer and emitter, has attracted widespread attention due to its unique photophysical properties and enormous applications in photovoltaic cells, photocatalysis, bio-imaging, and photodynamic therapy. Particularly, in biological systems, long-wavelength excitation light can efficiently reduce the interference of background fluorescence and increase the penetration depth of biological tissue, thereby avoiding the use of high-energy excitation light and reducing the damage to biological samples. However, most of the upconversion dyes based on TTA mechanism are water-insoluble organic compounds, which greatly limits their application in the biological field. Herein we synthesized a TTA upconversion system based on silica nanoparticles, which can achieve upconversion emission in water. Specifically, the photosensitizer (fluorinated tetraphenylporphyrin platinum) and the emitter (siloxane derivatized 9,10-diphenylanthracene) for photon upconversion were designed and synthesized, whose upconversion performance in dichloromethane solution was firstly studied by UV-Vis spectrophotometer and fluorescence spectrometer. Clear blue upconversion emission from emitter could be observed when the photosensitizer was excited by 532 nm laser. The triplet energy transfer efficiency between photosensitizer and emitter is 60%. The optimal ratio of photosensitizer to emitter was 1∶40. Based on this ratio, the stable upconversion silica nanoparticles with uniform size in water were constructed by micellar template method. The average diameter characterized by transmission electron microscopy (TEM) is 15.5 nm and the hydration diameter characterized by dynamic light scattering (DLS) is 22.5 nm. When the 532 nm laser is used as the excitation source, the upconversion emission in water was achieved. Their upconversion luminescence lifetime and quantum yield are 12 μs and 0.8%, respectively. Finally, the upconversion mechanism in silica nanoparticles was studied. The upconversion intensities in silica nanoparticles show quadratic and first-order dependences on the incident intensity in the low and high excitation intensity ranges respectively, proving a triplet-triplet annihilation mechanism.