Heavy-atom effects on metalloporphyrins and polyhalogenated porphyrins

Abstract

The photophysics of halogenated and metallated tetrakisphenylporphyrins is investigated using single-photon counting, photoacoustic calorimetry and luminescence techniques. The radiationless transition rates in these and related molecules are interpreted with a quantum-mechanical tunnelling model modified to include the effect of spin-orbit coupling in the intersystem crossing rates. It is shown that tetrakisphenylporphyrins with halogens in the ortho positions have long-lived triplet states that are formed in high yields. Ó

Visible‐Light Photoactive, Highly Efficient Triplet Sensitizers Based on Iodinated Aza‐BODIPYs: Synthesis, Photophysics and Redox Properties

“…can induce spin orbit coupling due to the heavy atom effect, thus facilitating intersystem crossing. [16,17] An interesting group of organic chromophores that can be utilized ast riplet photosensitizers are aza-BODIPYs (aza-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene). [18,19] Structurally,a za-BODIPY dyes are derivatives of BODIPY (4,4-difluoro-4-bora3a,4a-diaza-s-indacene) dyes obtained by replacing the mesocarbona tom that connects both pyrrole rings with an azabridge.…”

Photooxidation of 4-chlorophenol sensitised by iron meso-tetrakis(2,6-dichloro-3-sulfophenyl)porphyrin in aqueous solution

“…19, 20 For example, it has been reported that the triplet quantum yield, Φ T , for meso-tetrakis (2,6-dichloro- † Dedicated to Professor Sebastião Formosinho on the occasion of his 60th birthday.…”

Halogen atom effect on photophysical and photodynamic characteristics of derivatives of 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin

“…The decrease of U D value with the insertion of more bromine atoms was already predicted for the Zn(II) complex of halogenated methoxyporphyrins [8]. The substitution in both ortho and para positions (PS4) has a negative effect on the singlet oxygen formation quantum yield.…”

“…With other halogen atoms some reports confirmed the expected superior behaviour for singlet oxygen formation, as expected from the heavy atom effect [8,32] but photocytoxicity was not studied.…”

“…For example, in Foscan Ò , currently in clinical use, all four phenyl groups have a hydroxyl substituent at the meta position [6,7]. One possible way to improve the therapeutic capability of the sensitizers is through the heavy atom effect [8] as shown in azadipyrromethene derivatives [9]. However, in vitro demonstration of the heavy atom effect in porphyrins is not confirmed.…”