Gold porphyrin

Andreasson, J., Kodis, G., Lin, S., Moore, A.L., Moore, T.A., Gust, Martensson, J. and Albinsson, B. (2002) The gold porphyrin first excited singlet state. Photochemistry and Photobiology, 76,... 

Gold porphyrins were first obtained by Rothemund et al. [97] in glacial acetic acid (Eq. 10). 

Gold - Water-soluble gold porphyrin ions, [Au(TPPS4)]3 and [Au(TMPyP)]5+ (as the 3- and 4-pyridyl isomers), were obtained from the respective free-base porphyrins in a mixture of water/pyridine/lithium chloride containing KAuCl4 [142]. The products were purified by extraction with acetone and methanol and subsequent HPLC, however, the counterions were not determined. 

Fig. 7 Principle oftransition metal-templated construction of a [2]-rotaxane with two different porphyrin stoppers. The white diamond is a zinc porphyrin, and the hatched diamond is a gold porphyrin. The black disk is Cu(i).

Upon excitation of the metal complex centre, triplet energy transfer to the donor appended porphyrin rapidly quenches the excited state of the central ruthenium bis-terpyridyl unit, whereas excitation of the gold porphyrin, leads in less than 1 ps to the triplet-excited state [23], which is unreactive to-... 

The first experiments in this direction were carried out on the triads 244+ and 254+ (Fig. 8), by exciting preferentially the metal centre around 340-355 nm. Excitation at this wavelength region produces to a predominant extent the excited state localized on the iridium complex unit, the ligand centered triplets PH2 - 3Ir - PAu or PZn - 3Ir - PAu [48]. Energy transfer to the porphyrin triplets dominates the deactivation of PH2 - 3Ir - PAu in 244+, with rate constants of 2.9 x 1010 s 1 for the transfer to the gold porphyrin localized excited state and ca. 1011 s 1 to the free base porphyrin localized excited state, respectively (Scheme 9). 

Kinetic studies have demonstrated that photo-induced electron transfer between the zinc and the gold porphyrin occurs at a rate of (1.7 ps)-1 in Cu(I)-complexed [2]-rotaxane 102, which is much higher than in the case of the free rotaxane 107 (36 ps)-1.73 The higher photoinduced electron transfer rate in the Cu(I) complex 102 than in the demetallated system 107 was explained also in terms of a superexchange mechanism. 

Fig. 24. Structures of cationic gold porphyrins which can bind to DNA and display photocatalytic nucleobase damage and double-strand cleavage controlled by visible light absorption (216,217).

A study of the photoredox reactions of some gold porphyrins has shown that chlorogold meso-tetralcis(4-W-methvlDvr idyl) -porphine tetrachloride is a durable catalyst for electron transfer processes Involving water. 

Rotaxanes made of a pendant gold-porphyrin macrocycle threaded inside a bis zinc-porphyrin stoppered dumbbell were built using a template approach, in order to assemble the two parts of the system, the dumbbell and the macrocycle. The template principle of construction is depicted in Fig. 11. 

The precursor C to the rotaxane E, called prerotaxane, is obtained in one step from a gold porphyrin macrocycle A and a difunctionalized thread B, thanks to the gathering properties of the transition metal (black dot). Construction of the porphyrin blocking groups is the kineticaUy templated key step leading to the metal-complexed rotaxane structure D. The desired rotaxane E is obtained after removd of the metal template from D. 

The photophysical properties of 33 +, 34+ and 35 + were investigated in DMF and the results are here summarized [72,75]. In these systems the redox active porphyrins are on different parts of the structure which are held together by the coordinated metal in 33 + and 35 +, whereas in 34+ they are held together only by mechanical bonds and no covalent electron-transfer pathways exist. These systems are characterized by some flexibility of the polyether gold porphyrin appended macrocycle which could cause, upon... 

Dimethylformamide, room temperature Excitation of the zinc porphyrin unit Excitation of the gold porphyrin unit... 

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