This is an important point, since in these three molecules the lowest excited singlet is a dark (i.e., optically forbidden) state. These molecules are therefore very weakly fluorescent, so that, in spite of the ST inversion, they are of little interest for OLED applications. Upon lowering the symmetry, the S 1 state can acquire oscillator strength, and, if ST inversion is maintained, extremely promising fluorescent dyes for OLED with 100% internal quantum efficiency could be devised.