Photophysical Studies of 1,2-C70H2

Photophysical measurements have been made on 1,2-C 70 H 2, the most stable isomer of the simplest C 70 derivative. This dihydride's electronic absorption spectrum is more diffuse than that of C 70 . Red shifts in the fluorescence and phosphorescence emission spectra show that excitations to the lowest singlet and triplet electronic states require approximately 8% less energy in 1,2-C 70 H 2 than in C 70 and that the S 1 −T 1 gap of 1,2-C 70 H 2 is ca. 310 cm -1 smaller than that of the parent fullerene. The dominant peak in the dihydride's T n ← T 1 near-infrared absorption spectrum falls at 1050 nm. Compared to the corresponding transition of C 70, this absorption feature is broadened, red-shifted by 75 nm, and reduced in peak molar absorptivity by a factor of 2. Derivatization of C 70 to form 1,2-C 70 H 2 accelerates T 1 decay by more than an order of magnitude, giving an intrinsic triplet lifetime of 2.0 ms at room temperature. The rate constant for triplet deactivation through ground state self-quenching is near 7.6 × 10 7 M -1 s -1, or approximately twice that of C 70 .