Porphyrin-BODIPY light harvesting [3]rotaxane

A light harvesting [3]rotaxane comprising of a central Zn porphyrin and four boron dipyrrin (BODIPY) moieties was constructed via the threading of alkyne substituted dibenzyl ammonium axle into dibenzo-24-crown-8 macrocyles of Zn-porphyrin followed by stoppering the resulting [3]pseudorotaxane with four azide functionalized BODIPY molecules via "click" reaction. Steady-state fluorescence studies demonstrated an efficient photoinduced energy transfer from BODIPY moieties to the central Zn porphyrin within [3]rotaxane. The innovation of new synthetic strategies to assemble functional materials is of the utmost importance. Herein, a light harvesting [3]rotaxane 7 was designed and synthesized by threading alkyne-functionalized dibenzyl ammonium 5 into dibenzo-24-crown-8 ether macrocycles of Zn porphyrin 4 followed by stoppering the resulting [3]pseudorotaxane 8 with four azide-functionalized boron-dipyrrin (BODIPY) 6 moieties through the copper(I)-catalyzed Huisgen alkyne-azide 1,3-dipolar cycloaddition (CuAAC "click" reaction). The photophysical properties of the resulting [3]rotaxane were investigated by UV-Vis absorption and fluorescence spectroscopy. The absorption spectrum of 7 demonstrated that both Zn porphyrin and BODIPY moieties of 7 retain their spectroscopic properties thus indicating negligible interaction between them in the ground state. In addition, fluorescence studies of the resulting [3]rotaxane 7 showed that the selective excitation of BODIPY moieties of 7 resulted in an efficient photo-induced energy transfer from the four peripheral BODIPY to the central Zn porphyrin thus imitating the natural photosynthesis processes.