Regulate The Self-assembled Monolayers Charge Transport Through Molecular Non-covalent Interaction

The goal of molecular electronics is to incorporate molecules into electronic devices and to construct functionally molecular electronic devices.In the electronic device,the molecules can exist in the form of self-assembled monolayers or single molecule.Molecular electronic devices are complex systems that consist of at least two electrodes,a molecular component,and two(different)molecule/electrode interfaces.The molecular interactions are widespread.The molecular interactions are weak interactions,which deeply affect the molecular function,such as the charge separation in the early stage of photosynthesis,the binding of subatrates with enzymes,the stabilization of protein delicate structures.At the same time,the molecular functions are closely related to its charge transport.Understanding the relationship between molecular interactions and charge transport is critical for designing molecular electronic devices with specific functions.The project employed the ordered molecule monolayers as models,which were constructed by self-assembled technique and characterized by ellipsometry,atomic force microscope,and polarization modulation-infrared reflection-absorption spectroscopy.We use the ’EGaIn’ technique to construct AuTS/SAMs//GaOx/EGaIn junctions and then test the electronic properties of these junctions.The project mainly explores the regulation of charge transport by intermolecular interactions from three perspectives.The research contents and relevant conclusions of this project are shown as follows:1.The non-covalent interactions regulate the charge transport of the hepta-peptide.In a series of lysine-substituted hepta-glycine peptide SAMs,we demonstrated systematic modulation of the noncovalent interaction by shifting the position of the charged lysine residue and the protonation conditions.Decreasing the hydrogen bonding or electrostatic interactions inside the peptide SAMs and increasing the electrostatic interactions with environmental counterions amplified the charge transport of the peptide junctions.Our results show that peptide junctions with polar or charged groups can modulate charge transport according to the environmental dynamics.Our results provide insights into the in situ modulation of charge transport properties for the development of bionanoelectronics.2.In peptide/quantum dots(QDs)bilayers,the electrostatic interaction between the peptide SAMs and QDs SAMs can improve the charge transport across the bilayer junctions.And then,the discrimination of QDs with the same bandgap as well as different ligands was achieved.We selected the CdSe/ZnS quantum dots(QDs)coated by-NH2,-COO-and-OCH3 as the research objects.The zeta potential of the QDs can be regulated by changing its surface groups.The current density values for these three types of QDs SAMs are the same.Then we constructed the heptapeptide/QDs bilayers and performed current density tests.The results showed that the current density across bilayers decreased compared with the QDs SAMs.Among the bilayers,the electrostatic interaction between the-OCH3 QDs SAMs and the peptide SAMs is the weakest.The current density value of the bilayer is reduced to 1/104 of the original value.The-COO-QDs have the strongest electrostatic interaction with the peptide SAMs,and the current density is only reduced to 1/10.The reason for this result is that the formation of the bilayers increases the molecule-electrode energy offsets and the current density of the bilayer junction is reduced.However,the electrostatic interaction between the QDs SAMs and the peptides SAMs can attenuate the increased energy offsets,enabling the three types of QDs with different current densities.Using the intermolecular interaction between QDs and biomolecules,our work provides a new idea for rationally designing molecular electronic devices with QDs as well as a new strategy for developing semiconductor devices.3.The charge transport of the host-guest complex is positively related to the host-guest interaction strength.We chose pillar[5]arene(P5A)with a hydrophobic cavity as the host molecule and constructed ordered SAMs on AuTS.Then we designed six types of guest molecules(MV,PyPh,MV-Ada,PyPh-Ada,TEA-Ada,and Mia-Ada)to form host-guest complexes with P5A.Here,the charge transport in the molecular solid state is related to the host-guest interaction(electrostatic and π-π interactions)in the solution.The binding constant(K)in the solution has a positive correlation with the solid-state charge transport.The trend of Gibbs free energy(ΔG)of the host-guest complex is consistent with the molecule-electrode energy gap(ΔE(U)),where the ΔG is derivated from K and ΔE(U)is obtained from ultraviolet photoelectron spectroscopy(UPS).The value of the HOMO-LUMO gap reduces after the guest molecule is inserted into the host cavity.The host-guest complex has more delocalized frontier orbitals than the host molecule,which is beneficial to the charge transport.These findings will open a new avenue to developing high-performance tunable supramolecular electrostatic devices and substrate specific sensors.