Application Of Delayed Fluorescence Dyes Based On Fluorescein Derivatives

Thermally activated delayed fluorescence molecules（TADF）feature with long-lived delayed fluorescence due to not only efficient intersystem crossing（ISC）ability but also efficient reverse intersystem crossing（RISC）at room temperature.As a new type of luminescent material,it has achieved successful application on organic light emitting diode（OLED）.The benefits of its high-efficiency ISC and microsecond-life long-lived triplet lifetime characteristics as a new generation of photosensitizer applications has been less studied.Therefore,this paper studies the application of fluorescein derivatives TADF molecules with excellent photophysical properties as a photosensitizer in triplet-triplet annihilation upconversion（TTA-UC）and fluorescence imaging and photodynamic therapy（PDT）.A TTA-UC system by selecting fluorescein derivative DCF-MPYM with TADF properties as the photosensitizer and perylene or 9,10-diphenylanthracene as the emitter achieves a large anti-stokes shift upconversion emission from red light to blue with a high up-conversion emission quantum yield.The TADF photosensitizer DCF-MPYM has a very smallΔE_ST,which means a relatively small energy loss during the intersystem crossing process,and result in a very large anti-Stokes shift（207 nm）photon up-conversion.At the same time,DCF-MPYM itself has a long triplet lifetime（23.89μs）and a large molar extinction coefficient,which determines the high conversion efficiency（11.2%）in TTA-UC.For the first time,the potential of TADF fluorescein derivatives as a new generation of photosensitizers for photon upconversion has been fully demonstrated.Based on a fluorescein derivative with good water solubility as a fluorophore,two fluorescent probes named DCF-N₁ and DCF-N₂ with TADF properties were synthesized by simplely covalent attachment of a target protein（carbonic anhydrase IX）inhibitor as a targeting group.The TADF properties of the two probes were demonstrated by prompt fluorescence and delayed fluorescence lifetime measurement.The ability that two probes can produce active species such as ¹O₃ in neutral phosphate buffer（PBS）and cells was demonstrated by a commercialized active oxygen probe,which is the the key ingredient of PDT conditions.Furthermore,confocal imaging experiment showed that the two probes could specifically stain cells with high expression of carbonic anhydrase IX,but had no obvious fluorescence signal response to cells with low expression of target protein.Finally,MTT experiments confirmed that two probes have a certain photodynamic therapy effect.