Accounting for effects of nuclear motion is particularly important in cases of strong electron-vibration coupling. Usually, in organic molecules the electronic transitions (typically vel > 10,000 cm -1 ) are well-separated from vibrational transitions (vn ≤ 3200 cm -1 ), with much broader and more intense signals. In radical cations of π-conjugated porphyrin oligomers this distinction is less clear, with both electronic and vibrational transitions producing very intense signals in the 1500-6000 cm -1 region. These unusually strong vibrational transitions can be detected using infrared (IR) spectroscopy, and they are usually called IR active vibrations (IRAVs). Recently, IRAVs were experimentally found at ~1330, ~1550 and ~2080 cm -1 (shaded area in Figure ) in the butadiyne-linked porphyrin dimer 1 •+ (Figure ), and tentatively assigned to normal modes shown in Figure . Movement along these IRAVs was attributed to the strong coupling of vibrational modes with the singly occupied molecular orbital (SOMO). Here, we investigate this coupling in more detail by analysing how normal modes in 1 •+ modulate orbital energies (Figure ). Using the same density functional as in previous work (LC-wPBE ), we calculated the couplings between the HOMO and SOMO energies and normal modes in 1 and 1 •+ and compared them with computed dipole moment changes with respect to normal modes (i.e. infrared intensities) dD/dQi (Figure ).