Research On Molecular Regulation And Chemical Sensing Application Of Organic Conjugated Sensor Materials

In recent years,the pollution of the environment and food by harmful chemical substances is becoming a major problem in our society.Sensors that can effectively detect these harmful chemical substances are the key to solving this problem.Chemical sensors have been playing an increasingly important role in national defense technology,industrial production,environmental sanitation,food safety,and all aspects of daily life.Existing chemical sensors have high manufacturing costs.Some high-precision sensors also have limitations such as large size and complex operation,which cannot meet the current needs in some specific occasions（such as low cost,rapid detection,etc.）.Organicπ-conjugated molecules have become the core of research in the fields of conduction,photoelectric conversion,luminescence,self-assembly,and multidimensional materials due to their inherent electronic properties and rigid structure.Organic semiconductor materials and their applications in various electronic devices have developed rapidly.Since the properties of organic semiconductor materials are easily affected by the external environment,they have received widespread attention as the active layer of sensors.The morphology and microstructure of the film can be affected by molecular control during the device preparation process,which in turn affects its sensing performance.The introduction of side chains or specific groups can change the chemical structure of organic semiconductors and the arrangement of molecules.Studying the influence of these factors on the performance of organic semiconductor sensors and exploring its mechanisms will help fabricate high-sensitivity organic semiconductor chemical sensors.In addition,we need to look for other materials that can effectively detect specific harmful substances.Metal-organic frameworks（MOFs）that combine stability and sensitivity,with large specific surface area,easy-to-control topological structure,and high porosity are natural gas identification and detection materials.However,currently developed chemical sensors based on electron conductive MOFs（EC-MOFs）still have the problems of long reaction time,insufficient sensitivity,and difficulty in detecting redox neutral organic gas molecules.The reason lies in the response mechanism of the sensor.The MOFs layer adsorbs gas molecules,and then the molecules and the metal nodes undergo an electron transfer process to generate a sensing signal.New sensing mechanisms are required to achieve enhanced sensing performance.We have developed ion-conducting metal-organic frameworks（IC-MOFs）based chemical sensors,which use metal ions as carriers to directly react with the target analyte.We need to use new sensing mechanisms to develop chemical sensors with new structures.The main goal is to realize simple and reliable detection of ambient gas based on MOFs films as the sensing layer.Improving the electrical performance and chemical characteristics of the device can make it have high sensitivity and high selectivity for specific detection of target substances.This article has studied chemical sensors based on organicπ-conjugated molecular materials,explored the application of organic semiconductor materials and MOFs materials in chemical sensing.Through the means of molecular regulation,the sensing performance of chemical sensors were enhanced.The sensor realized the effective detection of a variety of harmful chemical components.The research content and results of each part are as follows:Firstly,the organic field-effect transistor sensor was decorated with biurea receptor to detect the leakage of LIB electrolyte.Chemical sensors based on a single organic semiconductor film cannot effectively detect redox neutral gas molecules,and have low sensitivity.A specific receptor group biurea was introduced on the surface of the sensing layer.Chemical sensors of organic semiconductors with and without receptors were prepared.Diethyl carbonate was used as the detection target.The composite sensor showed much higher sensitivity than the pristine one without receptors,and can effectively detect a small amount of LIB electrolyte leakage within a few seconds.The detection limit for DEC was 1.4 ppm,and 200 n L electrolyte can be detected.The response and recovery times for DEC at 600 ppm were 15 s and 90 s,respectively.Theoretical calculations further confirmed the hydrogen bond model between the receptor molecule and diethyl carbonate.And real-time detection of the real battery pack leakage was realized.High-performance organic field-effect transistors based on the receptor layer were of great significance to the development of new sensing technologies.Secondly,a modified liquid phase/liquid phase epitaxial self-assembly spray method was used to prepare a new type of ion-conducting MOFs film.Unlike the previously reported MOFs that use electrons as charge carriers,IC-MOFs use metal ions as charge carriers to detect changes in ion conductivity and dielectric properties.And a new type of chemical sensor based on the unique IC-MOFs film was fabricated,which realized the detection of LIB electrolyte leakage.Compared with the previous chapter,it achieved breakthroughs in sensitivity,response speed and detection limit.The detection limit for DMC was 50 ppb,and limited detection of 20 n L of electrolyte can be achieved with a response time of less than 2 s.Through experimental analysis,the conduction and sensing mechanism of the sensor was further studied.Metal ions are the key factor of sensing performance.Due to the ion conduction characteristics,the sensor can operate in chemical resistor mode and chemical capacitor mode in addition to current as the output signal.Therefore,we have compared various sensing signals.In AC voltage mode,the sensor has higher sensitivity,more stable baseline and faster response time.Thirdly,using the ionic conductivity of the IC-MOFs film and using the output capacitance as the sensing signal,a high-performance humidity capacitive sensor was prepared.The direct interaction between metal ion carriers and water molecules is one of the key factors in the sensing mechanism of humidity sensors.We adjusted the types of different metal ions and organic ligands,fabricated a series of IC-MOFs humidity sensors,and compared their humidity sensing performance.The above-mentioned new type humidity sensors based on IC-MOFs have the advantages of wide detection range,good stability,and fast response and recovery speed.The humidity detection range was0-97%RH,and the response time and recovery time were 2.5 s and 1.5 s,respectively.It further developed the application of the humidity sensor in human respiratory monitoring,non-contact sensing,and flexible wearable fields.The above results indicate that the IC-MOFs humidity sensor provides a direction for the development of improved sensing materials that can be applied in the field of gas/humidity sensing.Fourthly,IC-MOFs based sensors were developed to detect cadaverine and meat spoilage.The sensor shows ultra-high selectivity to cadaverine.The sensor exhibited an irreversible response,while the sensor’s response to common volatile organic compounds（VOCs）was reversible.And IC-MOFs sensors based on different types of metal ions(Cu²⁺,Co²⁺,Ni²⁺,Zn²⁺,Mg²⁺)all showed effective irreversible responses to cadaverine.This is due to the direct interaction between cadaverine and metal ions.The complexation reaction leads to an irreversible decrease in capacitance.Metal ions play a key role in sensitivity and high selectivity.The IC-Cu THPP-MOFs sensor with copper ions as carriers showed the best performance,providing strong experimental support for mechanism research.Cadaverine in volumes as low as 20 n L can also be efficiently detected within seconds,with a response time of 13.5 s for 1μL of cadaverine.In addition,the sensor exhibited good equipment uniformity,long-term work stability and work repeatability.Therefore,our research reveals the influence of molecular regulation on the electrical and sensing performance of organic conjugated sensing materials from different research perspectives,in order to achieve the goal of improving the sensitivity,selectivity and stability of the sensor.This paper provides new directions and ideas for the further development of chemical sensors.