Photochemical properties of enediyne-cored dendrimers bearing naphthalenes at the periphery

A novel series of trans and cis enediyne-cored dendrimers bearing naphthalenes at the periphery were synthesized and their photochemical properties were examined. The trans/cis isomer ratio in the photostationary state was dependent on the excitation site in the dendrimers. When the enediyne core was selectively excited, the trans/cis isomer ratio in the photostationary state was either around 50/50 or a cis-rich mixture in all dendrimers due to the larger molar extinction coefficient of the trans-enediynes. On the other hand, when naphthalene was excited, a trans-rich mixture was unexpectedly obtained in higher generation dendrimers even though the energy transfer efficiency was almost quantitative in the trans dendrimers. These results could be explained by the energy transfer process, which was different depending on the geometric isomerism of the enediyne core.