Unusually Slow Intermolecular Proton-Deuteron Exchange in Porphycene

The rates of the intermolecular exchange of two internal protons by deuterons have been determined for alcohol solutions of porphycene and its 2,7,12,17-tetra- t -butyl derivative using femtosecond pump-probe polarization spectroscopy. The process is very slow, requiring approximately twenty hours to substitute both protons by deuterons in more than 90% of the molecules dissolved in bulk EtOD or BuOD at 293 K. Equal rates were found for the exchange of the first and the second proton.