Measurements of energy gap at the level anti-crossing region of the photo-excited triplet state of organic molecules

By the application of zero-field magnetic resonance (ZFMR)/FID technique and fast-field sweeping around the level anti-crossing region with fixed rf frequency, we obtained the (minimum) energy gaps between the two crossing levels as 16.7±2.0 and 14.3±3.7 MHz for pentacene-h14 in p-terphenyl and pentacene-d14 in p-terphenyl, respectively, when B0∥x. The minimum energy gaps occur at 14 mT for both systems. The hyperfine interaction contributes only partially to the observed energy gap.