Assembly of Tailored Thiophene Oligomers on Gold Electrodes - Film Formation and Properties
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Assembly of Tailored Thiophene Oligomers on Gold Electrodes - Film Formation and Properties Peter Anthony Collier1, Theivanayagam Chairman Deivaraj1, Wai Tat Kerk1, Wee Shong Chin2, Kian Ping Loh2, Ping Bai3, and Er Ping Li3 1 Surface Technology Group, Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore, 638075, Singapore 2 Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore 3 Electronics and Electromagnetics Program, Institute of High Performance Computing, 1 Science Park Road, #01-01 The Capricorn, Science Park II, Singapore, 117528, Singapore ABSTRACT To examine the potential to apply chemically modified surfaces in organic thin film transistors (TFT), we report the synthesis and characterization of two tailored series of oligothiophene compounds. The oligomers have thiol end groups for coupling to gold electrodes and have regio-regular alkyl substitutions corresponding to Head-Head (HH-) and Head-Tail (HT-) molecular conformations. Variations in chain length, structures and end groups have enabled a detailed study of the deposition of films from solution and the films' properties. INTRODUCTION We have synthesized tailored oligothiophenes with functional groups, to study their propensities to chemisorb from solution, to form self assembled monolayers (SAMs) [1-6] and to determine the films' properties. The aim was to control the electrical transfer characteristics at interfaces by selection of the bonding chemistry [7] and through organisation of molecular packing at the surfaces. Here we refer to the synthesis of compounds shown in Table 1. Previously we reported the properties of films formed from monomers with different alkyl substitutions [8] and compared surfaces prepared with films of monomers and a dimer [9]. In this account, we include films formed from the higher oligomers and contrast the properties of the HH- and HT-series. {Note 1 T1SH}
Table 1. HH- (upper) and HT- (lower) series of thiophene oligomers Monomer1 C6H13
Dimer (T2SH) Tetramer (T4SH) C6H13 C6H13
C6H13 C6H13
Hexamer (T6SH) C6H13 C6H13
C6H13 C6H13
SH SH
S
S
2-mercapto-3hexyl-monomer C6H13
S
HH-dimer with thiol end group C6H13
2-mercapto-4hexyl-monomer
SH S
S
HT-dimer with thiol end group
S
S
S
HH-tetramer with thiol end group
C6H13
C6H13
SH S
SH S
C6H13
S
C6H13
S
SH S
C6H13
S
HT-tetramer with thiol end group
S
S
S
S
S
HH-hexamer with thiol end group
C6H13
S
C6H13 C6H13
C6H13 C6H13
SH
C6H13
S
C6H13
S
C6H13
S
C6H13
S
HT-hexamer with thiol end group
C6H13
S
S
SH
EXPERIMENTAL DETAILS Synthesis and analysis As-synthesized products were collected by liquid-liquid extraction and dried using a rotary evaporator. Purifications were performed using column chromatography. Analyses were completed to verify the compositions and structures, namely: NMR – structure determination; FTIR – functional groups; uv-visible – absorbance and optical properties; mass spectroscopy – accurate mass; elemental analysis – c
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