Photophysical properties of diphenyl-2,3-dihydroxychlorin and diphenylchlorin

The photophysical properties of 5,15-diphenyl-2,3-dihydroxychlorin (DPCOH) and 5,15-diphenyl-chlorin (DPC) in organic solution were studied. Absorption, fluorescence, triplet state and photobleaching experiments are reported. The ground states of both compounds show strong absorbance in red region (λ = 638 nm, ε = 35,000 M−1 cm−1 and λ = 645 nm, ε = 42,000 M−1 cm−1, respectively) and the singlet excited states show low fluorescence quantum yields of 0.0802 and 0.150 in benzene and the lifetimes are 7.38 and 10.18 ns, respectively. Absorption spectra of the triplet states were also measured and they have nearly the same triplet state lifetimes of 53 μs (DPCOH) and 50 μs (DPC). The triplet quantum yields are 0.82 and 0.75, respectively. The data of photobleaching quantum yields show that the presence of oxygen does not significantly affect the photobleaching. All the results demonstrate that both diphenylchlorines are good candidates for second-generation photosensitizer in photodynamic therapy.