Molecular Junctions Composed of Oligothiophene Dithiol‐Bridged Gold Nanoparticles Exhibiting Photoresponsive Properties

Abstract

Three oligothiophene dithiols with different numbers of thiophene rings (3, 6 or 9) have been synthesized and characterized. The X-ray single crystal structures of terthiophene 2 and sexithiophene 5 are reported herein to show the exact molecular lengths, and to explain the difference between their UV-visible spectra arising from the different packing modes. These dithiols with different chain lengths were then treated with 2-dodecanethiol-protected active gold nanoparticles (Au-NPs) by means of in situ thiol-to-thiol ligand exchange in the presence of 1 microm gap Au electrodes. Thus the molecular junctions composed of self-assembled films were prepared, in which oligothiophene dithiol-bridged Au-NPs were attached to two electrodes by means of Au-S bonded contacts. The morphologies and current-voltage (I-V) characteristics of these films were studied by SEM and AFM approaches, which suggested that the thickness of the films (3-4 layers) varied within the size of one isolated Au-NP and typical distance-dependent semiconductor properties could be observed. Temperature dependent I-V measurements for these molecular junctions were performed in which the films served as active elements in the temperature range 6-300 K; classical Arrhenius plots and subsequent linear fits were carried out to give the activation energies (deltaE) of devices. Furthermore, preliminary studies on the photoresponsive properties of these devices were explored at 80, 160, and 300 K, respectively. Physical and photochemical mechanisms were used to explain the possible photocurrent generation processes. To the best of our knowledge, this is the first report in which oligothiophene dithiols act as bridging units to link Au-NPs, and also the first report about functionalized Au-NPs exhibiting photoresponse properties in the solid state.

Functional Oligothiophenes: Molecular Design for Multidimensional Nanoarchitectures and Their Applications

“…76 Terthiophene 2.13 was prepared in 89% yield by reaction of R-terthiophene with bromine and KSCN. On the other hand, 5-bromoterthiophene was dimerized in a Ni-catalyzed homocoupling reaction followed by thiocyanation, giving sexithiophene 2.14 in 86% yield.…”

Properties of Thiol End‐Capped and Iodine‐Doped Sexithiophene Disulfide Semiconducting Polymers Bridging Nanogap Gold Electrodes

“…Sexithiophene terminal dithiol was prepared via the method that we have described previously. [ 13 ] The anhydrous solvents were drawn into a syringe under a fl ow of dry N 2 gas and were directly transferred into the reaction fl ask to avoid contamination. Analyses for carbon, hydrogen, and nitrogen were performed on a Perkin-Elmer 1400C analyzer.…”

“…Fabricating nanodevices using Au-S bonds between the gold electrodes and the thiol end-capped organic molecules has been proven to be a good strategy to effectively reduce the interfacial barrier. [13][14][15][16][17] On the other hand, the relative conductance of oligothiophenes can be changed by oxidizing or reducing them, or introducing a dopant into the bulk because the oligothiophene proconductors can become oligothiopheniums, which are much better conductors because of the unfi lled HOMO and a change in geometry which creates mid-gap states. [ 18 ] Formation of the disulfi de bond is an effective way to extend the length of oligothiophenes.…”

Fabrication of molecular hybrid films of gold nanoparticle and polythiophene by covalent assembly

“…In order to compensate for the low conversion efficiencies of organic solar cells based on pure conducting polymers films, Huang et al fabricated molecular junctions composed of oligothiophene dithiol-bridged AuNPs which exhibited distinct photoresponsive properties [23]. This is mainly due to the unique ability of AuNPs to store electrons, promoting charge separation and facilitating electron transport [24].…”