Phthalocyanine fluorescence quenching

Ng et al. first reported the axial ligation of zinc(II) l,8,15,22-tetrakis(3-pentyloxy) phthalocyanine (1) with meso-pyridyl porphyrins 2 and 3 in chloroform, which form the corresponding edge-to-face dyad and pentad, respectively [25], As shown by UV-Vis spectroscopy, the ground-state tt-tt interactions between the perpendicularly disposed macrocycles in these arrays are insignificant. Upon mixing of phthalocyanine 1, zinc(II) meso-tetra(/Molyl)porphyrin, and 4,4/-bipyridine in chloroform, the formation of a face-to-face hetero-dyad was also inferred by fluorescence quenching experiments. 

Hor and Popovic (1994) measured photogeneration efficiencies of dispersions of HOGaPc in poly (vinyl butyral) (PVB) by delayed-field collection and field-induced fluorescence quenching techniques. The HOGaPc polymorph was described as type V. The transport layers contained N,N -diphenyl-N,N -bis(3-methylphenyl)-(l,r-biphenyl)-4,4 -diamine. Like many phthalocyanines, HOGaPc exhibits a linear correlation of the photogeneration and field-induced... 

The phthalocyanines are still of some interest, and Ayers has interpreted the photoelectrochemistry of copper phthalocyanine in terms of the band-model for semiconductors. Menzel et alf have studied the photoconductivity and electrical field-induced fluorescence quenching in metal-free phthalocyanine films. Doping of the film increases charge-carrier photogeneration, and it seems likely that the mechanism is extrinsic, involving field-assisted exciplex dissociation. These are complicated materials, which are difficult to purify, and the mechanisms of carrier generation in polycrystalline and amorphous films are still obscure. The porphyrins and monolayer assemblies of chlorophyll on SnOj electrodes 2 72,273 ijggjj studied. 

Similarly, the dipyridyl perylenediimide 45 also axially binds to zinc(II) 1,8, 15,22-tetrakis(2,4-dimethyl-3-pentoxy)phthalocyanine (25) to form the corresponding 1 1 and 1 2 supramolecular complexes [48], The coordination of these two compounds has been monitored by UV-Vis, fluorescence, and 1H NMR spectroscopic methods. It has been found that the ligation of pyridyl ligand to zinc phthalocyanine is relatively weak and labile with a binding constant of 2,080 M-1 in CDCI3. The two components can mutually quench the fluorescence of their partner through an electron transfer process. 

Nucleobases and nucleosides are common motifs for hydrogen-bonded supramolecular arrays. Ng et al. first reported a series of phthalocyanine-nucleobase conjugates [64], The tetra-adenine phthalocyanine 64 was prepared by standard <9-alkylation of zinc(II) tetrahydroxyphthalocyanine with 9-(2-bromoethyl)adenine in the presence of K2CO3. The fluorescence of 64 is quenched substantially upon addition of thymine-substituted 9,10-anthraquinone 65, and the rate is much faster compared with that for the situation when the unsubstituted 9,10-anthraquinone is used as the quencher. These results suggest that 64 forms a supramolecular complex with 65 through the Watson-Crick base-pairing interactions. 

The fluorescence of the zinc-phthalocyanine core in dendrimer 49 is completely quenched [67]. On the basis of energetic considerations, this quenching process was attributed to electron transfer from the connected ferrocenyl units to the excited phthalocyanine core. The photophysical behavior of 50 and 51 was not mentioned. 

Phthalocyanines possessing w-alkanethiol moieties (20) form monolayers on the gold surface. The fluorescent emission from the monolayers can be quenched by NO2, which makes them potentially useful for sensing the environmentally important NO2. Interactions with NO2 can also be recorded by SPR measurements453 -455. 

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