Synthesis of bacteriochlorins bearing diverse β-substituents

Eleven bacteriochlorins have been prepared for surface attachment, bioconjugation, water-solubilization, vibrational studies, and elaboration into multichromophore arrays.

Synthesis of a Naphthalocyanine-Like Dye: The First Report on Zn(II)-1,6-methano[10]annulenecyanine

The synthesis of the new dye 1,6-methano[10]annulenecyanine is described. For this purpose, the 3,4-dicyano-1,6-methano[10]annulene and 3,4-carboxyimide-1,6-methano[10]annulene buildings blocks were synthesized in six to eight steps. In both cases, these building blocks were then cyclotetramerized to furnish a new Zn(II)-1,6-methano[10]annulenecyanine which presents a strong red-shifted absorption band at 800 nm and high solubility in common organic solvents.

Annulated bacteriochlorins for near-infrared photophysical studies

Bacteriochlorins with phenaleno or benzo annulation absorb at 913 or 1033 nm and exhibit excited-state lifetimes of 150 or 7 ps, suggesting applications in photoacoustic imaging.

Expanding π-Conjugation in Chlorins Using Ethenyl Linker

A series of chlorin monomers and dyads has been prepared to probe the effect of ethenyl vs ethynyl linkers on the electronic conjugation and optical properties in resulting derivatives. Styryl-substituted chlorins have been prepared either by a Heck reaction or by microwave-assisted olefin metathesis, while β-β ethenyl-linked dyads have been synthesized from the corresponding vinyl-substituted chlorin monomer using microwave-assisted olefin metathesis. It has been found that when an ethenyl linker is connected at the β-position of chlorin it provides stronger electronic conjugation than an ethynyl one, which is manifested by a greater bathochromic shift of the longest wavelength absorption (Q _y) and emission bands. Stronger electronic coupling is particularly evident for dyads, where ethenyl-linked dyad exhibits a strong near-IR absorption band emission (λ_abs = 707 nm, λ_em = 712 nm, Φ_f = 0.45), compared to the deep-red absorption and emission of a corresponding ethynyl-linked dyad (λ_abs = 689 nm, λ_em = 691 nm, Φ_f = 0.48). The reactivity of ethenyl-linked dyads with singlet oxygen is discussed as well. The results reported here provide further guidelines for molecular design of deep-red and near-IR absorbing and intensely emitting chlorin derivatives and chlorins with extended π-electronic conjugation for a variety of photonic applications.

Characterization of Hydroporphyrins Covalently Attached to Si(100)

Attachment of synthetic analogs of natural tetrapyrroles to electroactive surfaces enables physicochemical interrogation and may provide material for use in catalysis, diagnostics, and energy conversion. Six synthetic zinc chlorins and one free base bacteriochlorin, tailored analogs of chlorophyll and bacteriochlorophyll, respectively, have been attached to Si(100) via a high-temperature (400°C) baking method. The hydroporphyrins bear diverse functional groups that enable surface attachment (vinyl, acetyl, triisopropylsilylethynyl, pentafluorophenyl, and hydroxymethylphenyl) and a geminal dimethyl group in each reduced ring for stabilization toward adventitious dehydrogenation. The films were examined by cyclic voltammetry, FTIR spectroscopy, X-ray photoelectron spectroscopy, and ellipsometry. Monofunctionalized and difunctionalized hydroporphyrins gave monolayer and multilayer films, respectively, indicating robustness of the hydroporphyrin molecules, but in each case the film was more heterogeneous than observed with comparable porphyrins. The data suggest that some amount of unattached molecules remain intercalated with surface-attached molecules. Additional molecular designs will need to be examined to develop a deep understanding of the structure-activity relationship for formation of homogeneous monolayers and multilayers of synthetic hydroporphyrins.

Synthesis and Spectral Properties of meso-Arylbacteriochlorins, Including Insights into Essential Motifs of their Hydrodipyrrin Precursors

Synthetic bacteriochlorins-analogues of bacteriochlorophylls, Nature's near-infrared absorbers-are attractive for diverse photochemical studies. meso-Arylbacteriochlorins have been prepared by the self-condensation of a dihydrodipyrrin-carbinol or dihydrodipyrrin-acetal following an Eastern-Western (E-W) or Northern-Southern (N-S) joining process. The bacteriochlorins bear a gem-dimethyl group in each pyrroline ring to ensure stability toward oxidation. The two routes differ in the location of the gem-dimethyl group at the respective 3- or 2-position in the dihydrodipyrrin, and the method of synthesis of the dihydrodipyrrin. Treatment of a known 3,3-dimethyldihydrodipyrrin-1-carboxaldehyde with an aryl Grignard reagent afforded the dihydrodipyrrin-1-(aryl)carbinol, and upon subsequent acetylation, the corresponding dihydrodipyrrin-1-methyl acetate (dihydrodipyrrin-acetate). Self-condensation of the dihydrodipyrrin-acetate gave a meso-diarylbacteriochlorin (E-W route). A 2,2-dimethyl-5-aryldihydrodipyrrin-1-(aryl)carbinol underwent self-condensation to give a trans-A₂B₂-type meso-tetraarylbacteriochlorin (N-S route). In each case, the aromatization process entails a 2e^-/2H⁺ (aerobic) dehydrogenative oxidation following the dihydrodipyrrin self-condensation. Comparison of a tetrahydrodipyrrin-acetal (0%) versus a dihydrodipyrrin-acetal (41%) in bacteriochlorin formation and results with various 1-substituted dihydrodipyrrins revealed the importance of resonance stabilization of the reactive hydrodipyrrin intermediate. Altogether 10 new dihydrodipyrrins and five new bacteriochlorins have been prepared. The bacteriochlorins exhibit characteristic bacteriochlorophyll-like absorption spectra, including a Q_y band in the region 726-743 nm.

Synthesis and photophysical characterization of bacteriochlorins equipped with integral swallowtail substituents

The two pyrroline units of bacteriochlorins can now bear gem-dialkyl or diaryl groups (L), which project above and below the macrocycle plane, whereas dimethyl groups generally have been accessible previously.