Singlet oxygen quantum yields from halogenated chlorins: potential new photodynamic therapy agents

Abstract

Flash photolysis and photoacoustic calorimetry were used to measure the energy-transfer rates and singlet oxygen quantum yields originated by the triplet states of halogenated tetrakisphenylporphyrins and related chlorins in aerated toluene. The chlorins (λ max ≈ 660 nm, ε ≈ 3 × 10 4 M −1 cm −1 ) have long-lived triplet states (>12 s) in the absence of molecular oxygen, and in its presence the singlet oxygen production quantum yields of the 2-chloro and 2,6-dichlorophenyl derivatives are 0.89 ± 0.05 and 0.98 ± 0.02, respectively. The high absorptivity in the red, the photostability and the efficiency of these chlorins in producing singlet oxygen suggests a ground for the development of better sensitisers for photodynamic therapy.

Photosensitized singlet oxygen and its applications

“…Halogenated chlorins such as TDFPC 0/5,10,15,20-tetrakis(2,6-difluorophenyl)chlorin, ToCPC 0/ 5,10,15,20-tetrakis(2-chlorophenyl)chlorin, TDCPC 0/ 5,10,15,20-tetrakis(2,6-dichlorophenyl)chlorin have recently been investigated as potential new PDT agents [76]. The quantum yields of these complexes when excited at 655 or 660 nm are considerable: TDFPP F D 0/0.88, ToCPP F D 0/0.89, TDCPP F D 0/0.98.…”

Heavy-atom effects on metalloporphyrins and polyhalogenated porphyrins

“…Our PAC apparatus and the procedure employed in the measurements was recently described in detail [14,23]. In short, the sample and reference solutions, and the solvent, were flown separately with a 1 ml/min rate (SSI chromatographic pump) through a 0.11 mm thick cell.…”

“…We were unable to detect the phosphorescence of free-base porphyrins. Given their relatively long lifetimes, we assumed that their U T were identical to the corresponding singlet oxygen quantum yields in aerated solution, given by [14] …”

“…The present work was motivated by the need for better PDT sensitisers based on porphyrins, chlorins and bacteriochlorins [13][14][15], that is, sensitisers with high absortivity in the phototherapeutic window (600-900 nm) that generate singlet oxygen in high yields. The most important precursor of the O 2 ð 1 D g Þ state is the triplet state T 1 of the sensitiser.…”

Tissue Uptake Study and Photodynamic Therapy of Melanoma‐Bearing Mice with a Nontoxic, Effective Chlorin

“…Our interest in the series of 5,10,15,20-tetrakis(2-chloro-5-sulfophenyl)porphyrin (TCPPSO 3 H), [23] chlorin (TCPCSO 3 H) and bacteriochlorin (TCPBSO 3 H) [24][25] analogues comes from the knowledge that the chlorine atom in the ortho position of the phenyl rings promotes the efficient formation of long-lived triplet states in these photosensitizers, [26][27][28] thus favoring efficient energy transfer to molecular oxygen. Furthermore, these analogues possess improved stability imparted by this electron-withdrawing group, and good water solubility conferred by the sulfonic group.…”