Spectroelectrochemistry of Dendrimers: The Radical Cations of Low-Generation PAMAM-Like Dendrimers with a 1,4-Phenylenediamine Core As Studied by Electron Spin Resonance (ESR)/UV-Vis NIR Spectroelectrochemistry

TY - JOUR

T1 - Spectroelectrochemistry of Dendrimers: The Radical Cations of Low-Generation PAMAM-Like Dendrimers with a 1,4-Phenylenediamine Core As Studied by Electron Spin Resonance (ESR)/UV-Vis NIR Spectroelectrochemistry

AU - Zalibera, M.

AU - Rapta, P.

AU - Gescheidt, G.

AU - Christensen, Jørn Bolstad

AU - Hammerich, Ole

AU - Dunsch, L.

PY - 2011/3/17

Y1 - 2011/3/17

N2 - The role of dendrimer structure on the spin density distribution in radical cations was studied for five 1,4-phenylenediamine dendrimers, representing PAMAM-like dendrimer generations ranging from G-0.5 to G1.5, in DMSO and MeOH containing TBAPF6 using in situ ESR UV/vis/NIR spectroelectrochemistry. The radical cations were generated in DMSO by electrochemical oxidation at the first reversible oxidation peak or by AgNO 3 oxidation in DMSO and MeOH. The role of solvation was followed as the dendrimers are in general easier to oxidize in DMSO than in MeOH and the E1/2 differences were observed to increase with increasing dendrimer generation. In addition, an electrochemically irreversible second oxidation step was observed for the dendrimers in DMSO. Dendrimers terminated by a primary amine tend to block the electrode surface via the follow-up reaction products. The UV/vis/NIR spectra of both the electrochemically and chemically generated radical cations show two intense absorptions in the UV-vis range typical for Wurster's type radicals. The radical cations of all PAMAM-like dendrimers give ESR spectra with a g-factor of 2.0031 in DMSO and MeOH solutions. The ESR hyperfine data reflect the localization of the unpaired electron on the redox active PD core of the dendrimers, independent of the type or size of the terminal substituent. The lower resolution of the ESR signals with increasing molecular size points to a strong influence of the core substituents on the molecular-tumbling rate. ENDOR spectroscopy was used for the evaluation of the isotropic hyperfine coupling constants.

AB - The role of dendrimer structure on the spin density distribution in radical cations was studied for five 1,4-phenylenediamine dendrimers, representing PAMAM-like dendrimer generations ranging from G-0.5 to G1.5, in DMSO and MeOH containing TBAPF6 using in situ ESR UV/vis/NIR spectroelectrochemistry. The radical cations were generated in DMSO by electrochemical oxidation at the first reversible oxidation peak or by AgNO 3 oxidation in DMSO and MeOH. The role of solvation was followed as the dendrimers are in general easier to oxidize in DMSO than in MeOH and the E1/2 differences were observed to increase with increasing dendrimer generation. In addition, an electrochemically irreversible second oxidation step was observed for the dendrimers in DMSO. Dendrimers terminated by a primary amine tend to block the electrode surface via the follow-up reaction products. The UV/vis/NIR spectra of both the electrochemically and chemically generated radical cations show two intense absorptions in the UV-vis range typical for Wurster's type radicals. The radical cations of all PAMAM-like dendrimers give ESR spectra with a g-factor of 2.0031 in DMSO and MeOH solutions. The ESR hyperfine data reflect the localization of the unpaired electron on the redox active PD core of the dendrimers, independent of the type or size of the terminal substituent. The lower resolution of the ESR signals with increasing molecular size points to a strong influence of the core substituents on the molecular-tumbling rate. ENDOR spectroscopy was used for the evaluation of the isotropic hyperfine coupling constants.

M3 - Journal article

SN - 1932-7447

VL - 115

SP - 3942

EP - 3948

JO - The Journal of Physical Chemistry Part C

JF - The Journal of Physical Chemistry Part C

IS - 10

ER -