Synthesis And Photophysical And Chemical Properties Of NIR-Ⅰ Sulfhydryl Zinc Phthalocyanines

Photodynamic therapy(PDT)is a method of generating singlet oxygen by activating photosensitizers with specific wavelengths of light to cause cell damage and tissue necrosis.At present,this method has become a clinically recognized palliative anti-cancer technology.Photosensitizers are the key to PDT efficiency.Near-infrared Ⅰ(NIR-Ⅰ)photosensitizers have higher penetration efficiency,lower autofluorescence,and minimal photodamage to organisms due to their emission wavelengths in the range of 700-850 nm.higher,signal-to-noise ratio and detection sensitivity,and it has become a research hotspot.Most of the substituted zinc phthalocyanines reported so far introduce alkoxy and phenoxy groups into peripheral/non-peripheral positions through oxygen bridges.Although large substituents can reduce aggregation and improve solubility,their Q-band maximum absorption peaks are still located at 650-690 nm.In addition,the action site of the photosensitizer directly affects the therapeutic effect of PDT.Because the singlet oxygen generated during PDT treatment has a limited diffusion distance(<20 nm)and short lifetime(<40 ns),singlet oxygen generated in organelles by organelle-targeted photosensitizers can directly cause oxidative damage to organelles and trigger related cell death pathways,which is expected to effectively improve the photodynamic activity of photosensitizers.In this paper,a series of peripheral and non-peripheral thiol-substituted zinc phthalocyanines were synthesized by introducing targeted organelle groups through sulf bridge groups at the peripheral/non-peripheral positions of zinc phthalocyanine.On the one hand,functional groups with sulf bridge groups are introduced into the peripheral and non-peripheral positions of zinc phthalocyanine,and the conjugation effect of sulfhydryl electron-donating groups makes the Q-band absorption peak of zinc phthalocyanine red-shift to the NIR-Ⅰ region(700-850 nm),and on the other hand,sulf bridge-targeting organelle groups benzothiophene(targeting mitochondrial group),piperazine(targeting lysosomal group),morpholine(targeting lysosomal group)and triphenylamine(targeting lipid droplet group),which endows zinc phthalocyanine with specific organelle targeting function.The details are as follows:(1)Morpholine,benzothiophene,and piperazinyl were introduced into the peripheral and non-peripheral positions of zinc phthalocyanine through sulfur bridge substitution.The structures of six new thiol-substituted zinc phthalocyanines were synthesized and characterized.Including:tetra-(4/3-morpholine-1-biphenyl)mercaptozinc(Ⅱ)phthalocyanine(4ML-Zn Pc/3ML-Zn Pc),tetra-(4/3-(dibenzo[b,d)]thiophen-4-yl)phenyl)mercaptozinc(Ⅱ)phthalocyanine(4SF-Zn Pc/3SF-Zn Pc),tetrakis-(4-methylpiperazine-1-biphenyl)mercaptozinc(Ⅱ)phthalocyanine(4PIP-Zn Pc),tetrakis-(4-(2,3-diisocyanophenyl)-1-biphenyl)mercaptozinc(Ⅱ)phthalocyanine(3PIP-Zn Pc).(2)The photophysical and photochemical properties of six thiol-substituted zinc phthalocyanines were studied by UV-Vis and fluorescence spectroscopy.Compared with unsubstituted zinc phthalocyanine,the Q-band absorption peaks of the six phthalocyanines all have a red shift;the Q-band maximum absorption peaks of the non-peripheral substituted complexes are more red-shifted than those of the peripherally substituted complexes;The Q bands and the fluorescence spectra for the non-peripheral substituted zinc phthalocyanine(3ML-ZnPC,3SF-ZnPC,3PIP-ZnPC)were found at(706-714 nm)and(716-724 nm),which were located in the NIR-Ⅰ region.The fluorescence quantum yields and singlet oxygen quantum yields of the non-peripheral substituted zinc phthalocyanines were also higher than those of the corresponding peripherally substituted phthalocyanines.This may be due to the positional effect of the substituents,where the electron-donating sulfhydryl group acts as a bridge to link the morpholinyl,benzothiophene,and piperazine groups with zinc phthalocyanine to form a larger conjugated system,as a result,the energy gap between the highest occupied orbital(HOMO)and the lowest unoccupied orbital(LUMO)is reduced,resulting in a red shift of the absorption peak of zinc phthalocyanine and an increase in the fluorescence quantum yield.In addition,confocal laser imaging showed that peripheral thiol-substituted zinc phthalocyanines(4ML-ZnPC,4SF-ZnPC and 4PIP-ZnPC)could be uptaken by MCF-7 breast cancer cells and intracellular fluorescence signals were observed,further in vivo photodynamic activity being evaluated.Therefore,it is expected to become a photosensitizer for PDT imaging.(3)Triphenylamine and phenylcarbazole have large steric hindrance and conjugation system,which can avoid intermolecular aggregation of phthalocyanine and improve its photophysicalandphotochemicalproperties.Wesynthesized triphenylamine/benzcarbazole at the non-peripheral position of zinc phthalocyanine through sulfur bridge substitution and the structures of three complexes of triphenylamine and phenylcarbazole thiol-substituted zinc phthalocyanine were confirmed by FI-IR、~1H NMR and MALDI-TOF-MS.The three Including:tetrakis-(3-(diphenyl)-1-biphenyl)mercaptozinc phthalocyanine(3TPA-ZnPC),tetra-(3-(9-phenylcarbazole)-1-biphenyl)Mercaptozinc phthalocyanine(3Z-ZnPC)and tetrakis-(3-(3-(carbazole-9-phenyl))-1-biphenyl)mercaptozinc phthalocyanine(9H-ZnPC).The photophysical and chemical properties of the three phthalocyanines were compared by UV-Vis absorption spectroscopy and fluorescence spectroscopy.The Q-band maximum absorption peaks of triphenylamine and phenylcarbazole mercapto-substituted zinc phthalocyanine are located at 707-712nm,and the fluorescence maximum emission peaks are located at 718-720nm.The electron-withdrawing triphenylamine and benzocarbazole substituents are connected to the phthalocyanine ring through a sulfur bridge to form a conjugated system,which reduces the electron cloud density of the phthalocyanine ring,so that the maximum absorption and emission peaks of the three phthalocyanines are located in the NIR-Ⅰ zone.The fluorescence quantum yields of 3TPA-ZnPC,3Z-ZnPC and 9H-ZnPC were 0.38,0.49 and 0.41,respectively.The singlet oxygen quantum yields of 3TPA-ZnPC,3Z-ZnPC and 9H-ZnPC are 0.32,0.24,0.44,respectively.The fluorescence quantum yields of the three phthalocyanines are related to the structural planarity of the triphenylamine and benzocarbazole substituents.The planarity of 9-phenylcarbazole is higher than that of triphenylamine and 3-carbazole-9-phenyl,and 3Z-ZnPC possesses the highest fluorescence quantum yield.Using MCF-7 breast cancer cells as model cells,the cellular uptake and organelle localization of 3Z-ZnPC in MCF-7 breast cancer cells were imaged by confocal laser imaging.3Z-ZnPC can be taken up by MCF-7 cells and has bright fluorescence.3Z-ZnPC can colocalize with the specific fluorescent probe(BODIPY)of lipid droplets(Pearson correlation coefficient Rr=0.72,colocalization coefficient R=0.99).Further ex vivo photodynamic activity is being assessed.Therefore,3Z-ZnPC is expected to be a photosensitizer for targeting lipid droplets guided by fluorescence imaging in the NIR-Ⅰ region.