The Oxygen Sensing Mechanism Of Typical Cyclometalated Platinum??? Complexes And I₂-BODIPY

The identification and determination of oxygen is of great significance in many fields covered by chemical engineering.The conventional methods,standard iodometry and Clark electrode,are limited during application.Nowadays,the photochemical oxygen sensing method has been received increasing attention due to the characteristics of high sensitivity,good selectivity,simple way to pretreat sample,low requirement for the detection equipment,and non-consumption of analyte.In addition,it is free of electromagnetic interference,so the signals can be transmitted over a long distance,which means that it is an attractive candidate for on-line monitoring and remote control.Recently,dynamic collision theory is usually adopted to explain the oxygen sensing mechanism.However.not only the reaction between the oxygen moleculer and the luminescent material but also the effect on the luminescent properties by the reaction is unclear.Therefore.this paper investigates the reaction between the oxygen molecule and some luminescent materials under the excited state and try to illustrate the nature of the oxygen sensing from a different viewpoint.The research mainly included:(1)A trifluoromethyl-substituted cyclometalated platinum(II)complex(TSCP)is a typical material for oxygen molecule identification and determination.By applying density functional theory(DFT)method,the change of the luminescent mechanism before and after the combination was investigated via the frontier molecular orbitals and the electronic configurations of TSCP and the TSCP-O2 complex.We proposed a different quenching mechanism to explain the nature of oxygen sensing.According to the calculation results,the TSCP's luminescent mechanism is phosphorescent emission,and the TSCP-O2 complex internal conversion.While via time-dependent density functional theory(TDDFT)method,we calculated the excitation energy and the geometric optimization of TSCP and the TSCP-O2 complex under the excited state.The result indicates that the luminescence of TSCP is caused by localized excitation and that of the TSCP-O2 complex is delocalized excitation.We calculated the radiative and non-radiative rate constants of TSCP and TSCP-O2 complex and make their photophysical processes clear.(2)Triphenylamine-based cyclometalated platinum(?)(TCP)emits phosphorescence at room temperature.The phosphorescence was quenched by oxygen molecule,which means that TCP is another typical candidate for oxygen molecule recognition and measurement.By the way of quantum chemical calculation,we proposed a different quenching mechanism to elucidate the nature of oxygen sensing,which was different from the traditional dynamic collision mechanism.The luminescence mechanism of TCP involves phosphorescent emission,and the TCP-O2 complex fluorescent emission.By utilizing the DFT method,we calculated the electron configurations and the frontier molecular orbitals of-TCP and the TCP-O2 complex.Furthermore,applying the TDDFT method,we calculated the geometric optimization and the excitation energies of TCP and the TCP-O2 complex in the excited state.The results illustrate that the luminescence of TCP stems from localized excitation,while that of the TCP-O2 complex stems from delocalized excitation.Moreover,we also calculated the radiative and non-radiative rate constants of TCP and the TCP-O2 complex and clarified the photophysical processes of them.(3)I2-BODIPY is a good material for oxygen molecule identification and determination.By the way of quantum chemical calculation,we proposed a different phosphorescence quenching mechanism to elucidate the nature of oxygen sensing.The result indicates that I2-BODIPY and the oxygen molecule formed a triplet complex at first.Then the complex was excited to the triplet excited state.Finally,the triplet complex in the excited state jumped back to the ground state via non-radiative transition.The luminescent mechanism of I2-BODIPY is radiative transition and that of the I2-BODIPY-O2 complex is non-radiative transition.By applying the DFT and the TDDFT method,we calculated the frontier molecular orbitals and the electron configurations of I2-BODIPY and the I2-BODIPY-O2 complex.The calculated results illustrate that the luminescence of I2-BODIPY stems from localized excitation,while that of the I2-BODIPY-O2 complex stems from delocalized excitation.When I2-BODIPY combined with O2,the halogen bond formed.The halogen bond was strengthened in the excited state,which facilitate the non-radiative process.Moreover,we also calculated the radiative and non-radiative rate constants of I2-BODIPY and the I2-BODIPY-O2 complex and clarified the photophysical processes of them.The nature of the oxygen sensing of two typical cyclometalated platinum(II)complexes and I2-BODIPY were investigated in this paper.Aiming at the scientific issue of the hydrogen bond or the halogen bond in the excited state during oxygen sensing,the cyclometalated platinum(?)complex or I2-BODIPY combined with oxygen molecule was considered as an entirety—the hydrogen/halogen bond complex.According to the frontier molecular orbitals and the electron configurations of the hydrogen/halogen bond complex,the change of the luminescent mechanism before and after the combination between the luminescent material and the oxygen molecule was calculated.The behavior of the hydrogen bond or the halogen bond in the electronic excited state and its effect on the system luminescence properties were investigated.By applying time-dependent pertubation theory and Fermi's golden rule,the basic photophysics process of the system was explored.Accordind to the photophysics process,we proposed a different luminescence quenching oxygen sensing mechanism depicted as below.First,the three luminescent materials were combined with the oxygen molecule by producing a triplet state complex.Then,the complex was excited to the triplet excited state.Lastly,the complex jumped from the first excited state to the ground state via nonradiative transition.We believe that this new oxygen sensing mechanism would provide excellent theoretical support and guide for designing and developing new,more effective oxygensensing materials.