Intramolecular hydrogen bonding promoted excited state double proton transfer mechanism based on a typical molecule: Porphycene.

The double excited state intramolecular proton transfer (ESIPT) mechanisms of porphycene, were theoretically studied. The primary bond lengths, IR vibrational spectra and hydrogen-bond energy indicate that the intramolecular hydrogen bonds were strengthened in the first excited state, which facilitate the ESIPT processes. To elucidate the proposed mechanism, the potential-energy surfaces of the ground state and first excited state were constructed as functions of NH bond lengths and its relative torsional angle rotation. The intramolecular proton transfer of prophycene is more likely to occur through lengthwise pathway and proceed in the concerted coordinated transfer manner.