Time-resolved fluorescence and absorption techniques have been used to investigate energy and photoinduced electron transfer in a covalently linked free-base porphyrin−fullerene dyad and its zinc analog. In toluene, the porphyrin first excited singlet states decay in about 20 ps by singlet−singlet energy transfer to the fullerene. The fullerene first excited singlet state is not quenched and undergoes intersystem crossing to the triplet, which exists in equilibrium with the porphyrin triplet state. In benzonitrile, photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene competes with energy transfer. The fullerene excited singlet state is also quenched by electron transfer from the porphyrin. Overall, the charge-separated state is produced with a quantum yield approaching unity. This state lives for 290 ps in the free-base dyad and 50 ps in the zinc analog. These long lifetimes suggest that such dyads may be useful as components of more complex light-harvesting systems.

Large, inert, weakly basic carborane anions of the icosahedral type CHB11R5X6 - (R = H, Me; X = Cl, Br) allow ready isolation and structural characterization of discrete salts of the solvated proton, [H(solvent) x ][CHB11R5X6], (solvent = common O-atom donor). These oxonium ion Brønsted acids are convenient reagents for the tuned delivery of protons to organic solvents with a specified number of donor solvent molecules and with acidities leveled to those of the chosen donor solvent. They have greater thermal stability than the popular [H(OEt2)2][BArF] acids based on fluorinated tetraphenylborate counterions because carborane anions can sustain much higher levels of acidity. When organic O-atom donors such as diethyl ether, tetrahydrofuran, benzophenone, and nitrobenzene are involved, the coordination number of the proton (x) in [H(solvent) x ]+ is two. A mixed species involving the [H(H2O)(diethyl ether)]+ ion has also been isolated. These solid-state structures provide expectations for the predominant molecular structures of solvated protons in solution and take into account that water is an inevitable impurity in organic solvents. The O···O distances are all short, lying within the range from 2.35 to 2.48 Å. They are consistent with strong, linear O···H···O hydrogen bonding. Density functional theory calculations indicate that all H(solvent)2 + cations have low barriers to movement of the proton within an interval along the O···H···O trajectory, i.e., they are examples of so-called SSLB H-bonds (short, strong, low-barrier). Unusually broadened IR bands, diagnostic of SSLB H-bonds, are observed in these H(solvent)2 + cations.

The spectral characteristics of the fulleride(1-) anions of pyrrolidine-functionalized C 60 derivatives have been investigated in order to assess the degree to which the parent C 60 moiety retains its distinctive redox and chromophoric properties upon functionalization. Such comparison data are necessary if C 60 is to fulfill its anticipated role as a versatile electron-accepting chromophore and a multielectron reservoir. Three systems have been investigated: a simple, monomeric, Nmethylpyrrolidine derivative, 1, a pyrrolidine-linked tetraphenylporphyrin/C 60 dyad, 2, and a pair of bifullerenes, 3 and 4, with adjacent and remote dispositions of the C 60 moieties, respectively. Near infrared spectra of the fulleride(1-) ions of these derivatives are notably similar to C 60 1with only small energy shifts of the band envelope. 1 H and 13 C NMR data on 1 1are consistent with unpaired spin density confined largely to the C 60 moiety rather than delocalized onto the pyrrolidine functionality. The EPR spectra of all of the pyrrolidine-functionalized fulleride(1-) species are characterized by sharp doublets (∆H ) 1-2 G) and g values less than the free electron value. Unlike the EPR spectrum of C 60 1-, there is little temperature dependence of the line width. EPR evidence for ball-to-ball spin-spin interactions are observed in the fulleride of 3 but not in 4 or in the Cu II/ C 60 1metalated porphyrin dyad. The X-ray crystal structure of the porphyrin-C 60 dyad 2 has been determined. It is the first X-ray structural characterization of a pyrrolidinefunctionalized C 60 species and confirms that the azamethine ylide addition has occurred across a 6:6 ring juncture. The crystal packing of the dyad reveals an intermolecular interaction of the C 60 ball nestled in remarkably close approach to the porphyrin plane. The closest approach of a fullerene carbon atom to the mean plane of the porphyrin is ca. 2.75 Å. This interaction is notably similar to that envisaged for porphyrin-functionalized chromatographic supports used to separate fullerenes. A novel donor/acceptor relationship is proposed to account for this close interaction.