Discrepancy between common local aromaticity measures in a series of carbazole derivatives

The aromaticity of a series of carbazole derivatives has been analyzed by means of different local aromaticity criteria. In particular, the evaluation of the local aromaticity has been carried out through the use of structurally (HOMA) and magnetically (NICS) based measures, as well as by using a new electronically based indicator of aromaticity, the para-delocalization index (PDI), which is defined as the average of all Bader delocalization indices between para-related carbon atoms in a six-membered ring. For a series of carbazole derivatives, the three measures of local aromaticity vary in a rather narrow range. In addition, a clear divergence is achieved between the three aromaticity criteria. This makes it very difficult to reach a definite classification of the series of compounds with respect to their local aromaticity.