PDT-related photophysical properties of conformationally distorted palladium(II) porphyrins

Abstract

ABSTRACT:The photodynamic therapy (PDT) related photophysical properties of five palladium(II) porphyrins with increasing steric demand of the meso-substituents were investigated by steady state and time-resolved absorption and luminescence spectroscopy. The steric strain of the meso-substituents is reflected in a bathochromic shift of the Bband in the absorption spectra. In contrast to free-base porphyrins, the palladium(II) complexes exhibit only a very weak fluorescence with Φ Fl $10 À4. Instead, the corresponding triplet states of the porphyrins are formed via inter system crossing (ISC) with a quantum yield Φ ISC of nearly unity. A phosphorescence quantum yield Φ ISC of 10 À4 was determined assuming dynamic quenching. The triplet state of all compounds is efficiently quenched by molecular oxygen, generating singlet molecular oxygen with a quantum yield of Φ D $0.85. The various substitution patterns exerted no significant influence on the ISC rates or singlet oxygen quantum yields. Significant differences, on the other hand, were observed with respect to the triplet lifetimes, with a tendency of longer lifetimes for the porphyrins with sterically more demanding substituents (in air-saturated solution). All porphyrins were successfully incorporated into liposomes. The phototoxic activity of three compounds was investigated in cell suspensions. The use of the new porphyrinato-palladium(II) in PDT applications is discussed.

Photophysical characterization of imidazolium-substituted Pd(II), In(III), and Zn(II) porphyrins as photosensitizers for photodynamic therapy

“…The value of ε was calculated for three trials and averaged from the absorbance at the peak of the Soret band. The values (vide infra) agree with those in the literature [25–27]. …”

The Ionic Palladium Porphyrin as a Highly Efficient and Recyclable Catalyst for Heck Reaction in Ionic Liquid Solution Under Aerobic Conditions

“…Palladium porphyrins have found applications as luminescent markers [21], oxygen sensor [22], sensitizers for singlet oxygen formation [23], and photo-induced protein cross-linking agents [24], due to their high yield of intersystem crossing and long lifetime of the resulting triplet state in diverse media [25,26]. Anyway, the examples of palladium porphyrins as phosphine-free catalysts in C-C coupling reactions were few, except for the first case in the Suzuki reaction reported very recently [27].…”

Syntheses and Cellular Investigations of 173-, 152-, and 131-Amino Acid Derivatives of Chlorin e6

“…Heavy metal atoms in the core of the tetrapyrroles have been shown to facilitate intersystem crossing and increase the production of singlet oxygen due to the inner heavy atom effect. 36,37 …”