Polarization of fluorescence excitation has been measured both for free-base porphycene and three of its alkyl derivatives which differ by the length of their intramolecular hydrogen bonds. Examination of the measured anisotropy values reveals a rapid photoinduced tautomerization occurring in the lowest excited singlet state. The reaction rate is crucially dependent on the distance between the hydrogen-bonded nitrogen atoms. The process becomes too slow to be observed on a nanosecond time scale in the derivative with the largest N...N separation. A more detailed analysis of the anisotropy data makes it possible to determine the directions of the electronic transition moments.