Spin polarization and photoinduced electron transfer between ferrocene and fullerene derivatives containing a nitroxide group (original) (raw)
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Chemistry-a European Journal, 2007
Two new triads based on N-methylfulleropyrolidine, oligothienylenevinylenes (nTV) and ferrocene (Fc), namely C60-nTV-Fc (n=2, 4) have been synthesized. A HOMO–LUMO gap as low as 1.09–1.11 eV was experimentally determined by cyclic voltammetry. In both polar and nonpolar solvents, photoinduced charge-separation (CS) processes in C60-nTV-Fc predominantly take place from the singlet excited states of C60 and nTV; this result was indicated by steady and time-resolved emission spectroscopy. In the case of C60-4TV-Fc, the CS state was indicated by the nanosecond transient absorption spectra. In C60-2TV-Fc, although the CS process was also confirmed by the fluorescence quenching in nonpolar and polar solvents, the lifetimes of the CS states were shorter than those of C60-4TV-Fc. It was revealed that the introduction of Fc donor moiety at the end of the longer nTV chain in the C60-nTV dyad systems effectively increases the CS efficiency and the lifetimes of CS states.
The Journal of Physical Chemistry B, 2006
A rotaxane tethering both fullerene (C 60) and ferrocene (Fc) moieties (abbreviated as (C 60 ;Fc) rotax+) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ethersecondary amine motif. In (C 60 ;Fc) rotax+ , the C 60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C 60 and Fc in (C 60 ;Fc) rotax+ have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Nanosecond transient absorption measurements of the rotaxane demonstrated that the charge-separated state (C 60 •-;Fc •+) rotax+ is formed mainly via the excited triplet state of C 60 in polar solvents. The lifetime of (C 60 •-;Fc •+) rotax+ was evaluated to be 20 ns in dimethylformamide (DMF) at room temperature. With lowing temperature, the lifetime of (C 60 •-;Fc •+) rotax+ extends to 270 ns in DMF at-65°C, due to the structural changes leaving C 60 •and Fc •+ at a relatively long distance in the low-temperature region.
Applied Magnetic Resonance, 1997
A sedes of C60 fullerene derivatives containing a nitroxide group has been photoexcited by short LASER pulses in the microwave cavity of a cw-EPR spectrometer. Strongly spin polarized signals have been observed, in glassy matrix as well as in liquid sotution, for both the ground electronic st.ate and the excited quartet state. In the quartet state the excitation resides in the fullerene part and the molecule constitutes a triplet-radical pair with the partner covalently linked. The absorptive or emissive character of the transitions is explained in terms of the mechanism of radicaltriplet interaction producing spin polarization. Opposite initial sign and polarization pattems are observed for molecules with different spacer between nitroxide and fullerene. The time evolution of the relevant sublevel populations is fitted by a kinetic model taking into account quartet deeay constants, quartet and doublet spin-lattice relaxation rates and branching ratios.
Chemical Physics, 2001
Photoinduced electron transfer was observed in a series of methylsulfanyl sexithiophene/fulleropyrrolidine composites deposited as ®lms. Paramagnetic states were observed by transient EPR spectroscopy in the microseconds time domain. The spectra displayed polarized lines with characteristic antiphase emission/absorption pattern of spin polarization and were assigned to spin correlated radical ion pairs (SCRP) formed by intermolecular electron transfer from sexithiophene donor to C 60 fullerene acceptor molecules. Also transient signals detected at selected magnetic ®elds showed phase eects that are typical of SCRPs. Spectrum simulation was obtained by allowing for a distribution of respective orientations of the dipolar axes and g-tensors of partners in a pair. Fitting parameters used for one composite were Dagb À135 lT and J agb 2X5 lT for dipolar and spin exchange coupling constants, corresponding to an interradical mean distance of 27.4 # A. Similar values were obtained for the other examined systems. Pair structure and dynamics suggest to ascribe the charge-separated state to a radical pair generated after a hopping of the electron±hole charges from a primary pair originated in neighbor molecular sites. Ó
Physical Chemistry Chemical Physics, 2006
Pyrazolino[60]fullerene covalently-linked to ferrocene and N,N-dimethylaniline groups has been prepared and studied using time-resolved spectroscopic methods. The fluorescence quenching of the C 60 moiety indicates that charge-separation takes place via the singlet excited state of the C 60 moiety in both polar and non-polar solvents. The charge-separated state, in which an electron is localized on the C 60 sphere and a hole is located on the whole donor moieties of ferrocene, pyrazole, and N,N-dimethylaniline groups, has been confirmed by nanosecond transient spectra in the visible and near-IR spectral region. The lifetimes of the radical ion-pairs are as long as 30-50 ns in both polar and non-polar solvents.
The Journal of Physical Chemistry A, 2001
Nitroxide free radical/[60]fullerene derivative liquid solutions photoexcited by visible laser pulses are investigated by time-resolved EPR. Both radical and triplet excited fullerene spin-polarized EPR signals are observed. Their time evolution is examined in terms of CIDEP effects due to electron spin polarization transfer from the initially polarized triplet to the nitroxide and to spin polarization generated by the radical triplet pair mechanism. Radical and triplet spin relaxation times and rate constants for the processes of polarization transfer and radical triplet pair mechanism are obtained.