Synthesis and Photophysical Characterization of Porphyrin, Chlorin and Bacteriochlorin Molecules Bearing Tethers for Surface Attachment

Abstract

The ability to tailor synthetic porphyrin, chlorin and bacteriochlorin molecules holds promise for diverse studies in artificial photosynthesis. Toward this goal, the synthesis and photophysical characterization of five tetrapyrrole compounds is described. Each compound bears a surface attachment group. One set contains three meso-substituted porphyrins that differ only in the nature of a surface-binding tether-isophthalic acid, ethynylisophthalic acid or cyanoacrylic acid. The other set includes a porphyrin, chlorin and bacteriochlorin each of which bears an ethynylisophthalic acid tether. The ester derivative of each compound was prepared for solution photophysical characterization studies. The photophysical studies include determination (in toluene or acetonitrile) of the electronic absorption and fluorescence spectra, fluorescence yield and lifetime of the lowest excited singlet state. The excited-state lifetimes range from 1 to 5.6 ns for the five compounds. The radiative rate constant for the excited-state decay was estimated from the photophysical data (fluorescence yield and excited-state lifetime) and from Strickler-Berg analysis of the absorption and fluorescence spectra. The synthesis and characterization of the tetrapyrrole compounds underpin their use as sensitizers in molecular-based solar cells.

Synthesis and Excited‐state Photodynamics of a Chlorin–Bacteriochlorin Dyad—Through‐space Versus Through‐bond Energy Transfer in Tetrapyrrole Arrays

“…In contrast, the intensity of the bacteriochlorin fluorescence (760 nm) in FbC‐pe‐FbB is similar to that found for reference compound FbB2 regardless of whether the chlorin or bacteriochlorin component of the dyad is primarily excited; the corresponding fluorescence yield is Φ f = 0.19 (Table 1). Similarly, the lifetime of the lowest‐energy ( Q y ) singlet excited state of the bacteriochlorin constituent of FbC‐pe‐FbB in toluene (τ = 5.4 ± 0.5 ns) is the same within experimental error as that measured for reference monomer FbB2 (5.7 ± 0.6 ns) or for an analogous 5‐methoxy‐15‐(arylethynyl)bacteriochlorin (Φ f = 0.16, τ = 5.3 ns) examined previously (68). Thus, upon excitation of the chlorin, energy flows in very high yield to the bacteriochlorin.…”

“…Several points regarding the absorption spectra are noteworthy. (1) The prominent low-energy feature (755 nm) in the spectrum of FbC-pe-FbB is exclusively the bacteriochlorin Q y (0,0) band, which is expected to have a molar absorption coefficient of $120 000 M )1 cm )1 by analogy with the results for a related bacteriochlorin (12,68). (2) The spectra of chlorin reference compounds FbC1, FbC2 and FbC5 (Chart 2, Scheme 3) are basically indistinguishable.…”

Photophysics of Glycosylated Derivatives of a Chlorin, Isobacteriochlorin and Bacteriochlorin for Photodynamic Theragnostics: Discovery of a Two‐photon‐absorbing Photosensitizer

“…These compounds exhibit different degrees of excited state decay via radiative, nonradiative internal conversion, and S 1 → T 1 intersystem crossing pathways that are also solvent dependent. A high fluorescence quantum yield indicates radiative S 1 → S 0 decay dominates, whereas a low fluorescence quantum yield suggests decay is predominantly nonradiative via internal conversion and S 1 → T 1 . The greater Ф f and radiative decay time constants and low time constant for nonradiative decay for CGlc 4 and IGlc 4 indicate that these conjugates may serve as fluorescent tags.…”

De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

“…The chlorins in Scheme 87 that contain a gem-dimethyl group include the following: (1) the naturally occurring Bonellin; (2) 111f , prepared by Jacobi 243 (see Schemes 37–40 for other examples); (3) 202 , which bears an isophthalic acid moiety designed for incorporation in solar cells; 275,276 (4) 203a , which bears a single benzoic acid unit (10-position) and a p -tolyl group (5-position); 299 and (5) 203b , which bears a single phosphonic acid unit (10-position) and a p -tolyl group (5-position). 261 Chlorin 202 was prepared from H 2 C-T 5 M 10 by 15-bromination (neutral conditions) followed by Sonogashira coupling.…”