The interaction of poly (<i>p</i>‐phenylenevinylene) with air

The exposure of poly( p ‐phenylenevinylene), PPV, to air affects its performance in polymer‐based light‐emitting devices. An investigation is described in which exposure to air is demonstrated to give rise to reversible affects associated with the absorption of water vapor, leading to determinal changes in the outer electronic structure (see also the cover of this issue). In particular the resulting increase in torsion angle is shown to lead to a reduction in conjugation. A method of preparing clean PPV films is proposed.