Design, synthesis and photostability of novel 1,8-naphthalimide PAMAM light-harvesting dendrons

This paper reports on the divergent synthesis, photophysical properties and photodegradation of novel PAMAM dendrons, core and peripherally functionalized with 1,8-naphthalimide fluorophores. The novel compounds were configured as light-harvesting antennae where the system surface is labeled with blue emitting 4-allyloxy-1,8-naphthalimide "donor" fluorophores capable of absorbing light and efficiently transferring the energy to a single yellow-green emitting 4-alkylamino-1,8-naphthalimide "acceptor" dye. The focal 1,8-naphthalimide fluorophores in the antennae were modified with a HALS fragment (2,2,6,6-tetramethylpiperidine or 1,2,2,6,6-pentamethylpiperidine) with a view to improve their photostability. Novel light-harvesting systems showed highly efficient energy transfer, depending on the volume of the core substituent. Due to the HALS fragments the chromophoric system of the novel antennae showed higher photostability, while the photostability of the PAMAM scaffold was found to be lower.