Surface-enhanced Raman scattering studies on C_(60) fullerene self-assemblies

摘要

Surface-enhanced Raman scattering (SERS) was used to investigate C_(6o) self-assembling in solvents like pyrrolidine (Py) and N-methyl-2-pyrrolidinone (NMP) as well as in binary mixtures of o-dichlorobenzene (DCB)/acetonitrile (ACN) and DCB/NMP.For a correct evaluation of the modifications of Raman spectra induced by the C_(60) aggregation,we have also presented the variations due to the measuring method,i.e.,the signal dependence of the metallic support type and the surface roughness.The interaction between C_(60) and the Au substrate,appearing as a chemical component in SERS generation,is mainly evidenced by a band at ~342cm~(-1).In the aggregated phase,the intermolecular interactions lead to a reduction in the parent I_h C_(60) symmetry as observed by a modified phonon spectrum.As a general feature,the spectral range below 800cm~(-1) is the most diagnostic for the aggregate assignment,the main indicative being the disappearance of the Raman bands associated to the radial vibration modes.SERS measurements have revealed two stages in the self-assembling of C_(6o) in NMP.In the beginning,charge-transfer molecular complexes that associate slowly in stable aggregates are formed by the binding of an NMP molecule to the C_(60) cage.These complexes are noticed in the SERS spectrum by the replacement of the original H_g(l) band at ~269cm~(-1) with two others at ~255 and ~246cm~(-1).In the aggregated phase,when using NMP and P as a solvent,the Raman spectrum reveals new bands that appear around 94 and 110-118cm~(-1),which are associated with the interball interactions.In a DCB/ACN solvent mixture,the self-assembling process is driven by weak van der Waals type forces and resembles a precipitation,yielding C_(60) clusters of different size.