Preparation And Characterization Of Self-assembly Monolayer Film Based On Thiol Porphyrins

The monolayers of several thiol-end functionalized tetraphenylphophines (SH-TPP) and metal tetraphenylporphines (SH-MTPP) were self-assembled on gold surfaces and identified by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy and contact angle. The results suggested that the SH-TPP and SH-MTPP could form high quality self-assembled monolayer (SAM) on gold surface. The SAM of SH-TPP blocked the electron transport from gold electrode to solution. With the length of the thiol-end link-spacer (alkyl group) increasing the electron transport ability of the SAM decreased due to the increased insulator properties of the alkyl chain. Comparing with the SAM of SH-TPP, the electron transport ability of the SAM of SH-MTPP increased, this was probably due to i) the insertion of metallic ions changed the molecular structure, the molecular structure of SH-MTPP played an important role for electron transport through the SAM, ii) the insertion of metallic ions increased the electron tunneling probability through the monolayer.A lot of references have been addressed self-assembly monolayer (SAM) of such porphyrins that in each porphyrin molecule there is only one thiol/thioacetate-end-functionalized groups (i.e., single "paw"), few references have been addressed SAM of that porphyrins in each molecule there are multi "paws". Here, we used tetra-[p-(3-mercaptopropyloxy)-phenyl] porphyrin (we call PPS4, in each PPS4 molecule there are four thioacetyl-end-functionalized groups (four "paws") as an example to display SAM of the molecule with multi "paws". Moreover, self-assembled nanojunctions of PPS4 were fabricated by using gold nanogap electrodes (gap width: ca. 100 nm) and PPS4. The nanojunctions exhibited nonlinear current-voltage characteristics, indicating that current could be injected from Au electrodes into PPS₄ by tunnelling. With the light on/off, the nanojunctions were capable of being switched between low/high impedance states and worked as nanometer scale photo switchers.