Photophysical properties of protonated poly(p-pyridine)

To probe the role nitrogen lone pair electrons play in the photophysics of poly(p-pyridine) (PPY) we have used a range of acidic ‘dopants’ to protonate the nitrogen sites on each ring and made observations on how this affects the optical properties of the resultant protonated PPY films. In general we find that sulphonic acids have the greatest effect, causing perturbations to both the ground and excited state properties of the PPY. These changes occur with only moderate reduction of the photoluminescence quantum yield (PLQY), whereas non-sulphonic acids cause a larger reduction in PLQY without significantly effecting the ground or excited state energy levels. These aspects of the photophysics of PPY can be described using a simple inter-ring torsion argument