Meso‐Biphenyl‐Linked, Near‐ and Far‐Infrared Emitting, Chlorin and Bacteriochlorin Dimers: Synthesis, Excitation Transfer, and Singlet Oxygen Production

Abstract

A series of meso‐biphenyl linked chlorin and bacteriochlorin dimers, derived from naturally occurring chlorophyll (Chl‐a) and bacteriochlorophyll (BChl‐a) were synthesized in 32 % to 44 % yields and characterized, as photosynthetic antenna mimics, and a new class of singlet oxygen producing agents. The dimers are characterized by absorption, fluorescence, electrochemical, spectroelectrochemical and computational methods to evaluate their physico‐chemical properties, and to identify ground and excited state interactions. Evidence of excited energy exchange among the chromophores in the dimer is derived from femtosecond transient absorption spectral studies. Rate constants for excitation hopping were in the order of 1011 s−1, indicating occurrence of efficient processes. Nanosecond transient absorption studies confirmed relaxation of the singlet excited chlorin and bacteriochlorin dimers to their corresponding triplet states (3Chl* and 3Bchl*). As predicted by the established energy level diagrams, both 3Chl* and 3Bchl* are shown to be capable of producing singlet oxygen with appreciable quantum yields (ϕSO∼0.3).

A Remarkable Difference in Pharmacokinetics of Fluorinated Versus Iodinated Photosensitizers Derived from Chlorophyll-a and a Direct Correlation between the Tumor Uptake and Anti-Cancer Activity

“…In the absence of direct excitation of triplet oxygen from the ground state to singlet oxygen, as this is a symmetry forbidden process, the 1 O 2 is often generated by chemical reactions or by photosensitization [35]. In the photosensitization process, light is absorbed by the photoactive pyropheophorbide dyes which will then transfer the absorbed energy via their triplet states to the molecular oxygen [36,37]. In the present study, we monitored singlet oxygen emission at ~1270 nm for these newly made sensitizers in O 2 -saturated toluene solution (see Figure 1b inset for spectra and the Section 4 for additional details), and the singlet oxygen quantum yields (QY SO ) calculated as per the literature procedure are given in Table 1.…”

β-Pyrrole Functionalized Push or Pull Porphyrins: Excited Charge Transfer Promoted Singlet Oxygen Generation

“…Further, femtosecond transient absorption (fs-TA) spectroscopy has been utilized on selected compounds to examine the excited state charge transfer involving peripheral substituents. Finally, the photoluminescence in the near-IR region (1270 nm) of singlet oxygen ( 1 O 2 ) − produced by these porphyrins in dioxygen-saturated solutions has been monitored and quantified. Our findings show that both free-base and zinc porphyrins carrying push groups improve singlet oxygen generation, while those porphyrins carrying pull groups diminish singlet oxygen production.…”