A spectroscopic study of self-assembled monolayer of porphyrin-functionalized oligo(phenyleneethynylene)s on gold: the influence of the anchor moiety.
Porphyrin-functionalized oligo(phenyleneethynylene)s (OPE) are promising molecules for molecular electronics applications. Three such molecules (1-3) with the common structure P-OPE-AG (P and AG are a porphyrin and anchor group, respectively) and different anchor groups, viz. an acetyl protected thiol, -S-COCH3 (1), an acetyl protected thiol with methylene linker, -CH2-S-COCH3 (2), and a trimethylsilylethynyl group, -C(triple bond)C-Si(CH3)3 (3) have been synthesized and the corresponding self-assembled monolayers (SAMs) on Au(111) substrates have been prepared. The integrity and structural properties of these films were studied by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results suggest that the films formed from 1 have a high orientational order with an almost upright orientation and dense packing of the molecular constituents, i.e. represent a high quality SAM. In contrast, molecule 2 formed disordered molecular layers on Au, even though the molecule-surface bonding (thiolate) is the same as in the case of molecule 1. This suggests that the methylene linker in molecule 2 has a strong impact on the quality of the resulting film, so that a well-ordered SAM cannot be formed. The silane system, 3, is also able to bind to the gold surface but the resulting SAM has a poor quality, being significantly disordered and/or comprised of strongly inclined molecules. The above results suggest that the nature of the anchor group along with a possible linker is an important parameter which, to a high extent, predetermines the entire quality of OPE-based molecular layers.
Watcharinyanon
Somsakul
S
Department of Physics, Karlstad University, Karlstad, Sweden. somsakul@kau.se
Nilsson
Daniel
D
Moons
Ellen
E
Shaporenko
Andrey
A
Zharnikov
Michael
M
Albinsson
Bo
B
Mårtensson
Jerker
J
Johansson
Lars S O
LS
D000480:Alkynes / Q000138:chemical synthesis / Q000737:chemistry*; D004987:Ethers / Q000138:chemical synthesis / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission / Q000379:methods
D000480:Alkynes; D004987:Ethers; D011166:Porphyrins; C436384:phenyleneethynylene; D006046:Gold