A PYP chromophore acts as a 'photoacid' in an isolated hydrogen bonded complex.

ABSTRACT

The light-induced response of a neutral Photoactive Yellow Protein chromophore in a hydrogen-bonded complex with a proton acceptor has been studied by dual-detection action absorption spectroscopy and density functional theory. We show that the chromophore is a 'photoacid' and that ultrafast excited-state proton transfer might be operative in an isolated complex.