{'fraction_non_alphanumeric': 0.03533278553820871, 'fraction_numerical': 0.0008216926869350862, 'mean_word_length': 5.619565217391305, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Ultrafast Photophysics of Multiple-Resonance Ultrapure Blue Emitters.

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters are becoming increasingly attractive due to their applications in high-resolution organic light-emitting diode (OLED) display technology. Here, we present an investigation on the photophysics of two MR-TADF emitters (t-DABNA and TBN-TPA) by using quantum chamical calculation and ultrafast transient absorption (TA) spectroscopy. Compared with one-step structural planarization of t-DABNA, TBN-TPA undergoes two-step relaxation in S1 state, i.e., fast twisting of the peripheral group and subsequent restrained planarization of the B-N framework. The efficient twisting motion of the peripheral group largely reduces the energy level of the TBN-TPA system and correspondingly increases the barrier for subsequent planarization, which is favored for the narrowband emission. Our work provides a detailed picture for the excited-state deactivation of peripheral group-modified MR-TADF emitters without a pronounced charge-transfer (CT) characteristic mixed in the lowest-lying fluorescent state, which might be helpful for the future design of narrowband OLED emitters.