Design And Physical Properties Of Single-molecule Functional Electric Devices Based On Azulene Derivatives

Molecular electronics provides a "bottom-up" approach to developing functional electronic devices,where electron transport properties can be studied at the singlemolecule level.At present,the development of molecular electronics is still in the basic research stage.In order to realize the large-scale application of molecular devices,it is necessary to improve the performance of molecular devices to the level of practical applications.Therefore,how to improve the performance of molecular devices has become the key to the development of molecular electronics.Single-molecule is quantum scale.Therefore,the single-molecule device platform is an effective platform for quantum mechanism research.Using the quantum mechanism of single-molecule devices to develop new functional electronic devices is also a major feature of the development of single-molecule electronics.Azulene derivative molecules have rich optoelectronic properties and are widely used in optoelectronic device research,but the research at the single-molecule level is very limited.In this paper,a series of researches have been carried out on azulene derivative molecules,including the effect of molecular dipole moment on the performance of single-molecule field effect transistors,the effect of molecular dipole moment on charge transport mechanism and the mechanism of molecular dipole moment under electric field.These research works are listed as follows:First,in order to clarify the effect of molecular dipole moment on the performance of single-molecule field effect transistors,the azulene derivative molecule containing two azulene units and the naphthalene derivative molecule containing two naphthalene units were designed and synthesized.Azulene and naphthalene are isomers.In addition,azulene molecule has an intrinsic dipole moment,while naphthalene molecule has no intrinsic dipole moment.Therefore,the two derivative molecules are good contrast.We used the ionic liquid gate single-molecule field effect transistor device to carry out experimental measurement.The experimental results show that the single-molecule field effect transistor constructed by the azulene derivative molecule has a higher onoff ratio.The inherent dipole moment can effectively reduce leakage current.This study provides an effective method to improve the gate control capability of single-molecule transistors by introducing a symmetric dipole moment.Molecular dipole moment exhibits a modulation effect on current.In order to clarify the effect of molecular dipole moment on charge transport properties,a graphene-based single-molecule device platform was used to perform variable temperature Ⅰ-Ⅴ tests in the temperature range of 2 K～300 K.The effect of the intrinsic dipole moment in the azulene derivative molecule on the charge transport properties was analyzed by Arrhenius plot and F-N plot.The results show that the azulene derivative molecules can be excited by both temperature and electric field to generate a larger activation energy and show a stronger temperature dependence.So thermally excited transport occurs at lower temperatures.This study found that the introduction of a dipole moment in the molecule can enhance the activation and make the charge transport in the single-molecule junction more likely to exhibit a hopping transport mechanism.The effect of the electric field on the dipole moment can change the molecular configuration.In order to clarify the regulation mechanism of the electric field on the dipole moment,the azulene derivative molecule containing only one azulene unit was redesigned.Then,we used the graphene-based single-molecule device platform to monitor single-molecule current in real time at the temperature of 2 K.With the increase of the bias voltage,the current exhibits abundant changes.It shows different variation laws under positive bias and negative bias.According to the results of theoretical calculations,it is found that the azulene derivative molecules may undergo structural symmetry and resonance structural configuration transitions under electric field.Azulene derivatives have photoresponse,and if the quantum state transition is regulated by introducing light,it will open up ideas for the research and development of new optoelectronic devices.