Resonant Raman Spectroscopy of PAH-Os Self-Assembled Multilayers

N. TOGNALLI,; A. FAINSTEIN,; C. BONAZZOLA,; ERNESTO JULIO CALVO

JOURNAL OF CHEMICAL PHYSICS

Año: 2004 p. 1905 - 1911

0021-9606

We present a resonant Raman scattering study of (PAH–Os/PVS)n and (PAH–Os/GOx)mn and (PAH–Os/GOx)m self-assembled multilayers (n51–11 and m51 – 3). These Os polymer multilayers can be used in electrodes as efficient molecular wires for biomolecular recognition. The Raman intensity dependence on the number of self-assembly cycles provides information on the deposition process. The spectra are identical to that observed for PAH–Os in aqueous solution, indicating that the PAH–Os metal complex structure is conserved in the multilayers.We observe at ;500 nm incoming and outgoing Raman resonances of osmium and bipyridine vibrational modes. These resonances are associated to the metal-to-ligand charge transfer ~MLCT! transition. We study the evolution of these Raman modes as a function of the Os oxidation state during in situ electrochemistry. During the oxidation process, Os~II!!Os~III!, the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situn51–11 and m51 – 3). These Os polymer multilayers can be used in electrodes as efficient molecular wires for biomolecular recognition. The Raman intensity dependence on the number of self-assembly cycles provides information on the deposition process. The spectra are identical to that observed for PAH–Os in aqueous solution, indicating that the PAH–Os metal complex structure is conserved in the multilayers.We observe at ;500 nm incoming and outgoing Raman resonances of osmium and bipyridine vibrational modes. These resonances are associated to the metal-to-ligand charge transfer ~MLCT! transition. We study the evolution of these Raman modes as a function of the Os oxidation state during in situ electrochemistry. During the oxidation process, Os~II!!Os~III!, the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situ;500 nm incoming and outgoing Raman resonances of osmium and bipyridine vibrational modes. These resonances are associated to the metal-to-ligand charge transfer ~MLCT! transition. We study the evolution of these Raman modes as a function of the Os oxidation state during in situ electrochemistry. During the oxidation process, Os~II!!Os~III!, the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situ~MLCT! transition. We study the evolution of these Raman modes as a function of the Os oxidation state during in situ electrochemistry. During the oxidation process, Os~II!!Os~III!, the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situin situ electrochemistry. During the oxidation process, Os~II!!Os~III!, the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situ~II!!Os~III!, the Raman resonance related to the MLCT disappears and the bipyridine related modes harden by ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situ;10 cm21. These results are correlated with optical transmission measurements which show the disappearance of the visible region absorption when the Os complex is oxidized. We also find partial quenching of the Raman mode intensity after in situin situ voltamperometric cycles which demonstrates the existence of photo-electro-chemical processes.