Photophysical studies of selected carbon-84 isomers, carbon-80 species, aqueous carbon-60 colloid, and a carbon-60-amino acid derivative

Abstract

Ground- and excited-state studies of ill-characterized fullerenes are presented. The first isomerically enriched study of C84's major isomers finds they differ significantly in T1 energies. Their T 1 lifetimes span two orders of magnitude, from 643 mus for D 2(IV) to 5 mus for D2d(II). The minor isomer, Cs(a), has a 127 mus T1 lifetime. Temperature-dependent decay kinetics and triplet-triplet spectra also show clear isomeric variations. These changes are remarkable, since they originate in subtle geometry differences. The C80{D5d} isomer lacks appreciable transient absorption. Its slow quenching of 1Deltag O 2 emission indicates C80{D5d}'s T1 state is within 1 kT (∼300 cm-1) of 7880 cm -1. O2-quenching experiments showed that Ho 3N C80 {Ih}'s T1 energy lies above 7880 cm-1. This incar quenches C 70 triplet states, and data suggest their T1 energies are similar. The ground-state optical behavior of n-C60 (aq) is dominated by scattering effects. This colloid's transient attenuation is primarily refractive. Redshifted 1Deltag O2 emission from the colloid indicates the polarizable C60 environment lowers electronic energy levels. The "bucky amino acid" (BAA) shows derivatization-blueshifted transient absorption. This derivative has a T1 level substantially higher than 7880 cm-1, and is only a modest quencher of singlet oxygen.