Selective ratiometric pH-sensing PAMAM light-harvesting dendrimer based on Rhodamine 6G and 1,8-naphthalimide

• A PAMAM light-harvesting dendron of second generation, core and peripherally functionalized with Rhodamine 6G and 1,8-naphthalimide fluorophores is synthesized.
• The yellow-green emitting periphery of the antenna is designed as a PET based fluorescence probe.
• The system manifests excellent selective response to protons over representative metal ions in aqueous medium.
• Core emission intensity of the systems is enhanced by over an order of magnitude as a function of pH.
• The wavelength-shifting bichromophoric system acts as a highly selective ratiometric fluorescent pH probe in complex samples.

The paper reports on the divergent synthesis and fluorescence characteristics of a polyamidoamine (PAMAM) dendron of second generation. Novel compound is configured as a light harvesting antenna where the system surface is labeled with yellow-green emitting 4-(N-piperazinyl)-1,8-naphthalimide “donor” units capable of absorbing light and efficiently transferring the energy to a focal Rhodamine 6G “acceptor”. The energy transfer is calculated to 82%. Furthermore, the 1,8-naphthalimide periphery of the system is designed on the “fluorophore–spacer–receptor” format and is able to act as a molecular fluorescence photoinduced electron transfer based probe. Due to the both effects, photoinduced electron transfer in the periphery of the system and pH dependent rhodamine core absorption, novel antenna is able to act as a highly selective ratiometric pH fluorescence probe. Thus, the distinguishing features of light-harvesting systems (fluorescence resonance energy transfer) were successfully combined with the properties of classical ring-opening sensor systems.

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