Dynamics of the triplet state of phthalocyanine complexes of the platinum metals in zero field

Abstract

The luminescence properties of phthalocyanine complexes of platinum metals with d6 and d8 electron configurations were investigated in dilute solutions between room temperature and 1.6°K. For the first time it was possible to study the magnetic sublevels of the triplet state of aromatic molecules in zero field through optical detection methods alone. It was found that the lowest triplet state of these molecules has three zero field components of unequal splitting which depends on the central metal ion and which ranges from approximately 0.1–-10 cm−-1. Intersystem crossing populates solely the highest triplet component which does not radiate to the ground state, but which, in turn, populates the lower lying triplet components. The spin-lattice relaxation rates of these processes could be estimated to be of the order of 105 sec−1 at liquid helium temperature, and the triplet to ground state (S0← T1) decay rates were obtained. A noticeable solvent dependence of the radiationless rates was observed. The effect of spin-orbit coupling and radiationless energy transfer as a function of the metal ion in the phthalocyanine complexes is discussed. Surprisingly, Pd and Rh phthalocyanine were found to fluoresce as well as phosphoresce from essentially ligand-centered,excited states, an unusual occurrence in open d shell transition metal complexes.

Transition Metal and Rare Earth Compounds

“…This would correspond to the rate of k isc ª 1/t(S 1 ) ª 10 12 s -1 . A value of the same order of magnitude has also been determined for Pd-phthalocyanine [144].…”

The synthesis and spectral investigation of a novel highly water-soluble, aggregation-free antimony(V)-phthalocyanine absorbing light in optical therapeutical window

“…0.005 using that for H 2 tbpc (0.85) as the standard [39], of which the value is typical of antimony(V) Pcs [12,20,21,40] (this value is rather tentative because the emission range of this species was beyond the available range of the spectrophotometer used and hence the intensity of only the most intense emission band was evaluated). The low quantum yields are due to singlet-triplet intersystem crossing in the π-system due to a strong spin-orbit coupling induced by the presence of a heavy atom [17].…”

“…Such photosensitizers are required to have high 1 O 2 quantum yields as well as stability against the generated 1 O 2 . Antimony(V) Pcs are considered to be an excellent photosensitizer because of the presence of heavy atom (antimony), which would facilitate singlet-triplet intersystem crossing in their π system due to a metal-induced strong spin-orbit coupling [17]. Eventually, photophysical properties of antimony(III)-Pcs have been studied by Nyokong's group [18] and 1 O 2 -photosentizing ability of tetra-tert-butyl-substituted derivative has been exemplified in our earlier work [19].…”

Synthesis and properties of a highly soluble dihydoxo(tetra-tert-butylphthalocyaninato)antimony(V) complex as a precursor toward water-soluble phthalocyanines

“…Hence, the low yields seem characteristic of antimony-phthalocyanine complexes. It is known that the presence of heavy atom facilitates singlet-triplet intersystem crossing in the p-system due to a metal-induced strong spin-orbit coupling [10]. The singlet excited states of these derivatives are considered to be quenched by the presence of antimony ion in the center of their chromophore.…”

“…Such photosensitizers are required to have high 1 O 2 quantum yields as well as stability against the generated 1 O 2 . Antimony(V)-phthalocyanine derivatives are considered to be an excellent photosensitizer because of the presence of heavy atom like antimony, which would facilitate singlet-triplet intersystem crossing in their p system due to a metal-induced strong spin-orbit coupling [10], and because of their low p electron density [11][12][13][14], which would allow the photosensitizer to resist electrophilic attack by 1 O 2 or other photosensitized oxidants. In addition, such photosensitizing dye has to be very soluble in common solvents to be easily manipulated and also has to be solubilized in water by introducing hydrophilic group with one or more stable covalent bonds through their peripheral substituents and/or axial ligands.…”