Photophysical Properties of Mono- and Multiply-Functionalized Fullerene Derivatives

Abstract

Time-resolved and steady-state techniques have been performed to investigate the photophysical properties of C 60 [C(COOEt) 2 ] (Ia), e-C 60 [COOEt) (IIc), and e,e,e-C 60 [C(COOEt) 2 ] 3 (III) (e ) equatorial). Picosecond-resolved energy transfer to the fullerene core results in the rapid formation of the excited singlet state with remarkably blue-shifted singlet-singlet (S* 1 f S* n ) transitions (868 nm (III)) relative to pristine C 60 (920 nm). Intersystem crossing to the energetically lower lying excited triplet state exhibits a deceleration with increasing number of functionalizing addends. The corresponding triplet-triplet (T* 1 f T* n ) absorption energies also show a significant dependence on the degree and site of functionalization, spreading over a range of 100 nm (750 nm for 3 C 60 to 650 nm for e,e,e-( 3 C 60 )[C(COOEt) 2 ] 3 (III)). Energy transfer from radiolytically excited biphenyl ( 3 BP) to the fullerene's ground state corroborates the photolytic data. *0 f 0 Emissions from the lowest level of the excited singlet state (fluorescence) are mirror images of the reversed 0 f *0 absorption transitions with minor Stokes shift. Red shifts of fluorescence-and phosphorescence-related emission, relative to pristine C 60 , again sensitively reflect the perturbation of the fullerene's π-system as a function of the degree and site of functionalization. Cyclic voltammetry and reductive quenching of excited triplet fullerenes demonstrate that functionalization of C 60 obstructs the ease of reduction in the ground and excited triplet state. An increasing number of functional groups results in a cathodic shift of the redox potential (ground state -0.54 to -0.86 V; excited singlet state 1.44 to 0.91 V; excited triplet state +1.01 to +0.64 V Versus SCE for C 60 and e,e,e-( 3 C 60 )[C(COOEt) 2 ] 3 (III), respectively).

Photophysical Properties of Three Methanofullerene Derivatives

“…[34,35] For a number of pseudo-dihydrofullerenes, including cyclohexylfused and fulleroproline derivatives, the triplet absorption maximum is located at % 700 nm. [17,18,36±39] The energies of the observed triplet ± triplet absorption bands of C 60 in the 300 ± 800 nm region fit reasonably well with calculated values of allowed 3 H u 2 1 3 T 2g and 3 G u 2 1 3 T 2g transitions.…”

Photophysics and Photochemistry of a Water-Soluble C60 Dendrimer: Fluorescence Quenching by Halides and Photoinduced Oxidation of I-

“…Quenching values determined for two other C 60 methano derivatives, C 60 [C(CO 2 Et) 2 ] in toluene (τ ) 1.45 ns 25,26 ) and C 60 [C(CO 2 H) 2 ] 3 (eee) in water (τ ) 2.45 ns 25,26 ) are also reported for comparison. The important uncertainties associated with these values, especially in the case of C 60 [C(CO 2 H) 2 ] 3 , are due to the very weak fluorescence signals.…”

Energy and Electron Transfer in Polyacetylene‐Linked Zinc–Porphyrin–[60]Fullerene Molecular Wires

“…[40] The 880 nm transition decays with similar kinetics in the ZnP-(acetylene) n -C 60 dyads in toluene. The only component seen in the complementary nanosecond experiments was due to decay of 3 C 60 * (l max = 360, Figure 11.…”