Interactions between triiodide (I3-) and 4-tert-butylpyridine (4TBP) as postulated in dye-sensitized solar cells (DSC) are investigated by means of 13 C NMR and IR spectroscopy supported by DFT calculations. The charge transfer (CT) complex 4TBP·I 2 and potential salts such as (4TBP) 2 I + , I3- were synthesized and characterized by IR and 13 C NMR spectroscopy. However, mixing (butyl) 4 N + , I3- and 4TBP at concentrations comparable to those of the DSC solar cell did not lead to any reaction. Neither CT complexes nor cationic species like (4TBP) 2 I + were observed, judging from the 13 C NMR spectroscopic evidence. This questions the previously proposed formation of (4TBP) 2 I + in DSC cells.