Synthesis,Properties Of Group 9 Porphyrin-Aza-BODIPY NIR Dyes

Transition metal complexes show strong ISC contants and have attracted much attention owing to their applications in electroluminescence,oxygen sensing,triplet-triplet annihilation(TTA)upconversion and photocatalysis as triplet-state photosensitizer.However,The major drawback of using transition-metal complexes,which has strongly hampered the development of their potential applications,is that there are usually only weak absorption bands at the red end of the visible region and the neighboring portion of the NIR.Therefore,it is highly desirable to develop a series of NIR absorbing transition metal complexes.Fluorescenct dyes with strong absorption and emission in the near infrared(NIR)region have been the focus of considerable interest in recent years due to the excellent photophysical properties.In particular,the NIR dyes located at 650-1000 nm which is called the "biological window" have found unique advantages in cell labelling,biological imaging,cancer therapy and so on,which is mainly due to minimal autofluorescence and scattering interference from biological samples,and deep tissue light penetration in this spectra range.As a classical NIR chromophore,BF2-chelated tetraarylazadipyrromethene(aza-BODIPY)have been investigated intensively owing to their outstanding photophysical roperties,such as high extincition coefficient in the NIR region,good photostability,narrow and intense absoption and emission band,relative insensitivity fo changes in polarity.Singlet oxygen stays at the forefront of research because of its unique reactivity as a synthetic reagent,as an intermediate in oxygenation reactions of polmers and,perhaps most significantly,as a so-called "reactive oxygen species",ROS,in the photodynamic therapy.Up to now,there have been many kinds of photosensitizers which can produce singlet oxygen.However,some drawbacks strongly hamper their more wide applications,such as,their small molar absortion coefficients in the NIR region,poor photostability,low emission quantum yield due to strong inter system crossing,which has inspired us to design a new generation and more effective photosensitizers.The major results are summarized as follows:1.The synthesis of a series of novel orthogonally arranged conjugates la-c comprised of a rhodium(?)tetrakis-4-tolylporphyrin(Rh?(ttp))and a axial ligand BF2-chelated tetraarylazadipyrromethene(aza-BODIPY)linked by a covalent Rh-C(aryl)bond is described.This method fully exploits the advantages of strong inter system crossing of rhidum porphyrin and high molar absorption coefficients in the NIR region by forming an orthogonal conjugate with a direct metal-C bond and have successfully synthesized a series NIR absorbing transition-metal complexes with singlet oxygen production ability in solar solvent.The results clearly demonstrate that a series of photosensitizers with different absorption and emission wavlenghth can be synthesized by the structure modification of the aza-BODIPYs,it is because the changes in the energies of the fronitier MOs of aza-BODIPY result in the energy-level tuning of Rh?(ttp)-aza-BODIPY.The title compounds of Rh?(ttp)-aza-BODIPY show unprecedented excited-state behavior.This new class of material chanllenges our understanding of the behavior of excited electronic states and role of the heavy atom in intersystem-crossing processes.Although the presence of the heavy metal of rodium atom,the title compounds show remarkable photophysical properties:highly emissive singlet exicited states.The triplet excited states show no phosphorescence and transfer energy to oxygen to produce singlet oxygen.In the last,All the data suggest that luminescence and singlet oxygen production are independent,which is different significantly from other dyes in previous reports whose emission and singlet oxygen production is contradiction with each other.Therefore,this study is highly significant not only for the development of a far wider series of stable NIR absorbing with singlet oxygen generating ability materials,but also for the fundamental theory study.2.Although la-c compounds exhibit strong absorption in the NIR region and produce singlet oxygen efficiently,its low luminescence quantum yield strongly hamper their more wide applications,such as biological imaging.According to the theory calculation,efficient emission could be achieved by the change of aza-BODIPYs molecular orbital energy level.Then we introduced methoxy group to bromo-substituted aza-BODIPY,and further synthesized Rh?(ttp)-aza-BODIPY 1d-f.Experimental results show that luminescence quantum of ld-f are approximately ten times higher than that of la-c perhaps due to the strong electron-donating group of methoxy substituted attached to the aza-BODIPY,at the same time,their absorption and emission spectra are more red shifted,which will guide us in the design and synthesis a class of NIR absorption compounds with higher luminescence quanturm yield and strong singlet oxygen production ability.3.At the same time,based on the on/off switch mechanism of photo-induced electron transfer,we synthesized a kind of NIR dye with 1O2 generating ability.A photosensitizer(NEt2Br2BDP)whose fluorescence and 1O2 generation are pH activatable and implemented in NIR region have been succefully designed and synthesized by attaching diethylaminophenyl to aza-BODIPY core.Fluorescence and 1O2 generation would occur if amine protonated,as the photodinduced electron transfer mechanism would be switched off.Due to the strong donating group of amine,NEt2Br-2BDP show maximum absorption peak at 850 nm and red-shift about 200 nm relative to the aza-BODIPY core.Based on this photosensitizer,we have successfully synthesized an effective theranostic nanoprobe named as cRGD-NEt2Br2BDP NP to achieve highly selective in vivo tumor imaging,efficient PDT and therapeutic self-monitoring by encapsulating a newly designed NEt2Br2BDP in the cRGD-functionlized PEG-PLA nanocarrier.All the data suggest that this rationally designed and carefully engineered nanoprobe offers a new paradigm for precise tumor theranostics and may provide novel opportunities for future clinical cancer treatment.