Zero-field magnetic resonance of the photo-excited triplet state of pentacene at room temperature

The pulsed EPR free induction decay (FID) signals of the photo-excited pentacene triplet state are reported for three mixed crystals at room temperature: pentacene-h(14) in p-terphenyl, pentacene-h(14) in benzoic acid, and pentacene-d(14) in p-terphenyl. The recorded FID signals have relatively long decay times of about four microseconds, presumably due to the reduced hyperfine interactions in the zero magnetic field. The time domain FID signals transform to spectral components typically narrower than 500 kHz, allowing us to determine the pentacene triplet zero field splitting parameters to better accuracy than previously reported. Further, a new experimental technique using the high speed magnetic field jumping capability enables us to examine the anisotropic hyperfine and quadrupole interactions. (C) 2000 American Institute of Physics. [S0021-9606(00)00648-6].