Optical spectra and covalent chemistry of fulleropyrrolidines

Abstract

Low-temperature vibronic spectra of two fulleropyrrolidines (1-methyl-3,4-FP and 1-methyl-2(4-pyridine)-3,4-FP) embedded in crystalline toluene matrix have been studied. Two-component composition of the spectra has been established and chargetransfer-excitation origin of the structureless component has been suggested. Fine-structured Shpol'skii spectra were observed for 1-methyl-3,4-FP, which made possible to perform the vibrational analysis of its vibronic spectra. General similarities of the absorption spectra of fulleropyrrolidines and C 60 molecules along with significant difference in their details have been discussed. A detailed interpretation of the C 60 spectra serves as a basis for analyzing the spectra of the derivatives. Quantum-chemical study is based on the effectivelyunpaired-electron concept for the fullerene molecule. Computations have been performed for the singlet states of the molecules in unrestricted Hartree-Fock approximation implemented in AM1 semiempirical quantum chemical codes of the CLUSTER-Z1 software. The population of the HOMO and LUMO of the molecules under study alongside with the lowering of the molecules symmetry have been proposed to explain the spectral features observed.

10.1007/s11448-008-3004-2

“…All red spectra are well similar, particularly in terms of total intensity. They involve both the fluorescence and phosphorescence spectra of the fullerene molecules and for species I and II are described elsewhere [6] in detail. In the current study, these are regarded as internal standards for normalizing the intensity of the blue spectra in all series of experiments.…”

“…Oppositely, broadband structureless polar absorption forms the pedestal or background for the previous one. The analysis of the absorption spectrum structure from this viewpoint for the fullerene solutions in tol was initially performed in [6]. Similarly, a mirror-symmetric nonpolar component in the emission spectra involves the fluorescence and phosphorescence spectra of the solute molecules [6].…”

“…The analysis of the absorption spectrum structure from this viewpoint for the fullerene solutions in tol was initially performed in [6]. Similarly, a mirror-symmetric nonpolar component in the emission spectra involves the fluorescence and phosphorescence spectra of the solute molecules [6]. These spectra are positioned over a broadband spectrum of the polar component related to transitions from the lowest CT states to the ground state of the solution and all together form the red spectra discussed above.…”

“…1 plots the density of states of the spectrum over the whole Brillouin zone of the crystal [12], thus tagging the position of the CT states in the energy spectrum. According to the performed quantum-chemical (QCh) calculations (for calculation details, see [6]), the ionization potentials and electron affinities of fullerenes I and III are similar to those of C 60 , so that the plotted curve positions the CT energy spectrum for all of the studied solutions with an acceptable accuracy.…”

“…The difference in the relative intensities of the SERS in the two solutions clearly demonstrates the role of the DA interaction between the solute and solvent molecules, which is characterized by the coupling energy of -0.014 kcal/mol in tol and the repulsive interaction in ctcl. *QCh calculations have been performed in a semiempirical approach by using the AMI version of the CLUSTER-Z1 software (see details in [6]). The data for the ionization potentials are traditionally somewhat overestimated, while the electron affinities are well suited to the experimental data.…”