{'fraction_non_alphanumeric': 0.03156384505021521, 'fraction_numerical': 0.017934002869440458, 'mean_word_length': 4.8125, '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}}
Highly twisted carbazole-borane derivatives: B–N stereodynamic analysis and consequences on their emission properties

The stereodynamic properties of amino bis-mesityl-boranes bearing carbazole and benzocarbazole as the donor heterocycle have been investigated by dynamic NMR analysis and simulated by DFT calculations. The π-contribution to the B-N bond has been measured as 24 kcal/mol when carbazole is the donor heterocycle, while a value of 21.7 kcal/mol was determined for the benzocarbazole series. On these basis, two rotational barriers were determined for the B-N bond, the lower one (11.1-16.9 kcal/mol) leading to conformational enantiomers, and the higher one (21.0-24.0 kcal/mol) likely being responsible for the E-Z isomerization in compound bearing different aryl rings bound to the boron atom. It has been shown that both kinds of dynamic rearrangement involve a correlated motion of all the three rings. The difference in the ground state geometries and the different π-contribution led to pronounced variations in the fluorescence spectra, due to different geometric rearrangements in the TICT excited state. Stokes shift larger than 10000 cm-1 was observed in the carbazole series, with quantum yields up to 50%. It has been found that the π-contribution to the B-N bond in the excited state is still significant, with B-N isomerism likely not taking place in the ns scale.