Study On The Immobilization Of Triplet-Triplet Annihilation Upconversion Luminescent Materials

Photon upconversion based on triplet-triplet annihilation(TTA)is a technique that converts long-wavelength,low-energy photons into short-wavelength,high-energy photons.TTA has a wide range of applications,such as photovoltaic cells,photocatalysis,and biological imaging.Compared with the rare earth upconversion doped with lanthanides,TTA upconversion has obvious advantages:it can achieve higher quantum efficiency(3-40%)at low excitation energy;the absorption coefficient of the sensitizer is high;Under the premise of energy level matching,the excitation light wavelength and emission wavelength can be adjusted by selecting different sensitizers and acceptor molecules to convert photons in different long wavelength bands into short-wavelength high-energy photons.However,the efficiency of TTA upconversion has been limited by the following conditions:(1)The chromophores developed by TTA upconversion are all organic molecules or organometallic molecules,and the high-efficiency up-conversion process often occurs in deoxygenated organic solvents;(2)Because the high mobility of the chromophore is necessary to promote the energy transfer process of TTET and TTA,most solid materials are not the best matrix for TTA upconversion;(3)The TTA upconversion matrix should be free of oxygen,which would make the triplet excited photosensitizer easily quenched by oxygen,thus preventing the TTET energy transfer process.Obviously,these limitations are not conducive to the realization of TTA upconversion in oxygen-enriched water environment and solid matrix.In this paper,by using the micelle soft template method to encapsulate the sensitizer and receptor molecules in the titanium dioxide shell,a highly efficient upconversion nanocapsule(TTA-UCNP)based on triplet-triplet annihilation upconversion was successfully prepared.Choose diiodinated BODIPY and perylene as sensitizer and receptor,and soybean oil as solvent.These newly synthesized nanocapsules can not only maintain efficient chromophore mobility,but also reduce the quenching of triplet states by oxygen.Effective conversion of green light to blue light in the water phase.In the preparation process of nanocapsules,the effects of the amount of surfactant,acetic acid and butyl titanate on the up-conversion luminescence intensity of nanocapsules were studied.The analysis of the nanocapsule structure by TEM,SEM and XPS showed that the titanium dioxide layer was successfully coated on the microemulsion surface.Most of the current high-efficiency upconversion systems occur in deoxygenated organic solvents.In order to achieve low power,high efficiency and upconversion in the air atmosphere.We use DPA as the parent molecule and connect melamine derivatives with rich flexible alkyl chains on both sides via amide groups to obtain the acceptor molecule DPAM.In organic solvents,acceptor molecules can form supermolecules through hydrogen bonding,which can achieve efficient TTET and TTA processes.In the end,the supramolecular upconversion system can still clearly observe the upconversion emission in the organic solution without oxygen removal.This method can be applied to organic gels.We prepared Pt OEP/DPAM/CA ternary organic gel through multiple hydrogen bonding between DPAM receptor molecule and gel factor CA,and using Pt OEP as photosensitizer.The effects of solvent selection and gel concentration on the structure and upconversion emission intensity of up-converting ternary organic gels were studied.The results showed that when toluene was used as the solvent and the gel concentration was 13.5 m M,the gel performance was optimal.Due to the developed hydrogen bonding network and the internal nanofiber structure effectively blocking the entry of oxygen,the up-conversion gel exhibits high efficiency and stability,and the temperature response of the TTA upconversion can be achieved through the gel-sol circulation.Compared with most polymer-supported TTA upconversion,the deoxygenated upconversion ternary organic gel has a lower excitation threshold(35.39 m W/cm~2)and exhibits high efficiency upconversion emission at low excitation power.The upconversion quantum efficiency of the conversion ternary organic gel increases with the increase of excitation power,and finally reaches a maximum quantum efficiency of 6.7%around 160 m W/cm~2.