Non-conjugated dendrimers with a porphyrin core and coumarin chromophores as peripheral units: Synthesis and photophysical properties

Three porphyrin-cored dendrimers with non-conjugated coumarins as dendrons have been synthesized and characterized. The photophysical properties of the title compounds were investigated by means of UV/Vis absorption and fluorescence spectroscopy in dilute CH2Cl2 solutions and in thin neat films. The intramolecular energy transfer from the coumarin units to the porphyrin core clearly reveals two factors influencing energy-transfer efficiency. Firstly, a better spectral overlap between the absorption spectrum of porphyrin core and the emission spectrum of the coumarin moiety results in high energy-transfer efficiency. Secondly, a long alkyl side-chain improves solubility of dendrimers, but also prevents the coumarins from self-quenching. Hence, the dendrimer with N-octyl groups possesses a higher efficiency than that with N-ethyl groups. The dendrimers emit red light with higher fluorescence quantum yields over the free porphyrin.

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► Three non-conjugated dendrimers with a centered porphyrin were synthesized.
► Efficient energy transfer in dendrimers was observed, ΦFRET ∼99%.
► Two factors influencing energy-transfer efficiency were demonstrated.