Supramolecular Coordination Polymer Formed from Artificial Light-Harvesting Dendrimer

Abstract

We report the formation of supramolecular coordination polymers formed from multiporphyrin dendrimers (PZnPM; M = FB or Cu), composed of the focal freebase porphyrin (PFB) or cupper porphyrin (PCu) with eight zinc porphyrin (PZn) wings, and multipyridyl porphyrins (PyPM; M = FB or Cu), PFB or PCu with eight pyridyl groups, through multiple axial coordination interactions of pyridyl groups to PZns. UV-vis absorption spectra were recorded upon titration of PyPFB to PZnPFB. Differential spectra, obtained by subtracting the absorption of PZnPFB without guest addition as well as the absorption of PyPFB, exhibited clear isosbestic points with saturation binding at 1 equiv addition of PyPFB to PZnPFB. Job's plot analysis also indicated 1:1 stoichiometry for the saturation binding. The apparent association constant between PZnPFB and PyPFB (2.91 × 10(6) M(-1)), estimated by isothermal titration calorimetry, was high enough for fibrous assemblies to form at micromolar concentrations. The formation of a fibrous assembly from PZnPFB and PyPFB was visualized by atomic force microscopy and transmission electron microscopy (TEM). When a 1:1 mixture solution of PZnPFB and PyPFB (20 μM) in toluene was cast onto mica, fibrous assemblies with regular height (ca. 2 nm) were observed. TEM images obtained from 1:1 mixture solution of PZnPFB and PyPFB (0.1 wt %) in toluene clearly showed the formation of nanofibers with a regular diameter of ca. 6 nm. Fluorescence emission measurement of PZnPM indicated efficient intramolecular energy transfer from PZn to the focal PFB or PCu. By the formation of supramolecular coordination polymers, the intramolecular energy transfer changed to intermolecular energy transfer from PZnPM to PyPM. When the nonfluorescent PyPCu was titrated to fluorescent PZnPFB, fluorescence emission from the focal PFB was gradually decreased. By the titration of fluorescent PyPFB to nonfluorescent PZnPCu, fluorescence emission from PFB in PyPFB was gradually increased due to the efficient energy transfer from PZn wings in PZnPCu to PyPFB.

Aggregation-Induced Energy Transfer in a Decanuclear Os(II)/Ru(II) Polypyridine Light-Harvesting Antenna Dendrimer

“…[8][9][10][11][12][13][14] Among such systems, light-harvesting dendrimers play an important role. [15][16][17][18][19][20] In many cases, quite efficient photoinduced energy migration has been proved in dendrimers, even by means of pump-probe femtosecond spectroscopy. Some of us contributed to the field by designing one of the early families of light-harvesting dendrimers in which the chromophore subunits are mostly Ru(II) and Os(II) polypyridine complexes: [21][22][23][24] sub-picosecond energy transfer between nearby chromophoric units in the presence of suitable energy gradients occurred in such species.…”

Light‐Harvesting Nanotubes Formed by Supramolecular Assembly of Aromatic Oligophosphates

“…[1][2][3][4][5][6][7][8][9][10][11] In light-harvesting systems,e nergy is absorbed by numerous chromophores and transferred to an acceptor. Polymers [12][13][14][15][16][17][18][19] and dendrimers [20][21][22][23][24][25][26] were used to arrange multiple organic chromophores around acceptor molecules.E fficient transport of the excitation energy is ak ey aspect for the construction of effective light-harvesting systems. [27] Thed egree of structural order determines the level of electronic coupling and, thus,t he efficiency of energy transfer in chromophore arrays.…”

Light‐Harvesting Nanotubes Formed by Supramolecular Assembly of Aromatic Oligophosphates

“…In light‐harvesting systems, energy is absorbed by numerous chromophores and transferred to an acceptor. Polymers and dendrimers were used to arrange multiple organic chromophores around acceptor molecules. Efficient transport of the excitation energy is a key aspect for the construction of effective light‐harvesting systems .…”