Time-Resolved Studies of the Excited-State Dynamics of meso-Tetra(hydroxylphenyl)chlorin in Solution

Abstract

Meso-tetra(hydroxyphenyl)chlorin (m-THPC) is a new photosensitizer developed for potential use in photodynamic therapy (PDT) for cancer treatment. In PDT, the accepted mechanism of tumor destruction involves the formation of excited singlet oxygen via intermolecular energy transfer from the excited triplet-state dye to the ground triplet-state oxygen. Femtosecond transient absorption measurements are reported here for the excited singlet state dynamics of m-THPC in solution. The observed early time kinetics were best fit using a triple exponential function with time constants of 350 fs, 80 ps and > or = 3.3 ns. The fastest decay (350 fs) was attributed to either internal conversion from S2 to S1 or vibrational relaxation in S2. Multichannel time-resolved absorption and emission spectroscopies were also used to characterize the excited singlet and triplet states of the dye on nanosecond to microsecond time scales at varying concentrations of oxygen. The nanosecond time-resolved absorption data were fit with a double exponential with time constants of 14 ns and 250 ns in ambient air, corresponding to lifetimes of the S1 and T1 states, respectively. The decay of the T1 state varied linearly with oxygen concentration, from which the intrinsic decay rate constant, ki, of 1.5 x 10(6) s-1 and the biomolecular collisional quenching constant, kc, of 1.7 x 10(9) M-1 s-1 were determined. The lifetime of the S1 state of 10 ns was confirmed by fluorescence measurements. It was found to be independent of oxygen concentration and longer than lifetimes of other photosensitizers.

The Influence of Oxygen Depletion and Photosensitizer Triplet‐state Dynamics During Photodynamic Therapy on Accurate Singlet Oxygen Luminescence Monitoring and Analysis of Treatment Dose Response

“…The analogous data for ALA-PpIX were reported previously in Jarvi et al (12), but the rate constants were not determined and so are also now included in Table 2. The results are in good agreement with published values of k OT for mTHPC and porphyrin-based photosensitizers (27,28), which lie in the range 1.4-2.7 · 10 9 M M )1 s )1 . In order to model the in vitro kinetics, it was necessary to determine the changes in [ 3 O 2 ] that are due to metabolic rather than photochemical consumption.…”

Photodynamic Mechanisms induced by a Combination of Hypericin and a Chlorin Based‐Photosensitizer in Head and Neck Squamous Cell Carcinoma Cells

“…It is reported that the excited state for mTHPC in solution has an apparent triplet state life time of ca 250 ns in air . The triplet state life time for hypericin was found to be 370 ns .…”

Time-resolved microspectrofluorometry and fluorescence lifetime imaging of photosensitizers using picosecond pulsed diode lasers in laser scanning microscopes

“…16 From time-resolved fluorescence measurements in ethanol the lifetime of the lowest vibrational state of S 1 was assigned to 10 ns. 17 Using the LDH-C 400 for excitation, we observed a decrease in the fluorescence lifetime from 7.5 to 5.5 ns in the cytoplasm of cells during increasing incubation time. The different results To prove the results from time-resolved spectroscopy, the fluorescence lifetime of mTHPC was alternatively determined by TCSPC.…”