In the present study, photophysical properties of [N]phenylenes were studied by means of stationary and time-resolved absorption and fluorescence spectroscopy (in THF at room temperature). For biphenylene (1) and linear (1) and (2a) as "fast IC compounds", with k IC > 10 9 s -1 , and of (3) and (4) as "slow IC compounds", with k IC ≈ 10 7 s -1 , is suggested. This classification cannot simply be related to Hückel's rule-type concepts of aromaticity, because the group of "fast IC compounds" consists of "antiaromatic" (1) and "aromatic" (2a), and the group of "slow IC compounds" consists of "antiaromatic" (3b), (4) and "aromatic" (3a), (3c). The IC in the[N]phenylenes is discussed within the framework of the so-called energy gap law established for non-radiative processes in benzenoid hydrocarbons.2