A set of panchromatic absorbers exhibiting long excited-state lifetimes in both polar and nonpolar media has been prepared. The architectures are based on a porphyrin strongly coupled electronically to 1-4 perylene-monoimides via ethyne linkers. The constructs should find utility in molecular solar-conversion systems.

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The use of chlorins as photosensitizers or fluorophores in a range of biological applications requires facile provisions for imparting high water solubility. Two free base chlorins have been prepared wherein each chlorin bears a geminal dimethyl group in the reduced ring and a water-solubilizing unit at the chlorin 10-position. In one design (FbC1-PO3H2), the water-solubilizing unit is a 1,5-diphosphonopent-3-yl ("swallowtail") unit, which has previously been used to good effect with porphyrins. In the other design (FbC2-PO3H2), the water-solubilizing unit is a 2,6-bis(phosphonomethoxy)phenyl unit. Two complementary routes were developed for preparing FbC2-PO3H2 that entail introduction of the protected phosphonate moieties either in the Eastern-half precursor to the chlorin or by derivatization of an intact chlorin. Water-solubilization is achieved in the last step of each synthesis upon removal of the phosphonate protecting groups. The chlorins FbC1-PO3H2 and FbC2-PO3H2 are highly water-soluble (>10 mM) as shown by 1H NMR spectroscopy (D2O) and UV-vis absorption spectroscopy. The photophysical properties of the water-soluble chlorins in phosphate-buffered saline solution (pH 7.4) at room temperature were investigated using static and time-resolved absorption and fluorescence spectroscopic techniques. Each chlorin exhibits dominant absorption bands in the blue and the red region (lambda = 398, 626 nm), a modest fluorescence yield (Phi f approximately 0.11), a long singlet excited-state lifetime (tau = 7.5 ns), and a high yield of intersystem crossing to give the triplet state (Phi isc = 0.9). The properties of the water-soluble chlorins in aqueous media are comparable to those of hydrophobic chlorins in toluene. The high aqueous solubility combined with the attractive photophysical properties make these compounds suitable for a wide range of biomedical applications.

The extant biosynthesis of tetrapyrrole macrocycles has been considered a paradigm for the prebiotic formation of such molecules, yet only a few analogous non-enzymic reactions along the overall process have been demonstrated. In a prior study, the aqueous non-enzymic reaction of a dione and an aminoketone (d-aminolevulinic acid) afforded uroporphyrinogen, Nature's last universal precursor to all extant tetrapyrroles. Here, in one flask the non-enzymic combinatorial reaction of two diones (substituents = acetic acid and methyl) and two aminoketones (substituents = propionic acid and ethyl) yields four pyrroles, which upon subsequent combinatorial reaction afford a distribution of porphyrinogens. A software program for virtual library generation predicts 538 porphyrinogens from this [2 Â 2] reaction (owing to combinations and permutations) of which there are 25 sets of isomers based on condensed formulas of substituents. The collection spans the entire range of polarity enabled by the biosynthesis including uro-(number of carboxylic acids = 8), copro-(4), meso-( 2), and etio-porphyrinogen (0). The first two are successive intermediates in the extant biosynthesis, the latter two resemble in polarity the advanced biosynthetic products protoporphyrin and chlorophyll. Upon consideration of substituent patterns, the porphyrins (obtained by oxidation of the porphyrinogens) can be grouped into one of four polarity categories (predicted percentage): hydrophilic (0.4%), uncertain (83.6%), amphiphilic (15.6%), and hydrophobic (0.4%). HPLC and mass spectrometry data are consistent with expectations to the limit of analytical capabilities. Thus, in terms of the polarity of the tetrapyrrole macrocycles formed, an all-at-once non-enzymic combinatorial process recapitulates features of the stepwise biosynthetic pathway.

Chromophores that absorb and emit in the red spectral region (600–700 nm), are water soluble, and bear a bioconjugatable tether are relatively rare yet would fulfill many applications in photochemistry and photomedicine. Here, three molecular designs have been developed wherein stable synthetic chlorins – analogues of chlorophylls – have been tailored with PEG groups for use in aqueous solution. The designs differ with regard to order of the installation (pre/post-formation of the chlorin macrocycle) and position of the PEG groups. Six PEGylated synthetic chlorins (three free bases, three zinc chelates) have been prepared, of which four are equipped with a bioconjugatable (carboxylic acid) tether. The most effective design for aqueous solubilization entails facial encumbrance where PEG groups project above and below the plane of the hydrophobic disk-like chlorin macrocycle. The chlorins possess strong absorption at ~400 nm (B band) and in the red region (Qy band); regardless of wavelength of excitation, emission occurs in the red region. Excitation in the ~400 nm region thus provides an effective Stokes shift of >200 nm. The four bioconjugatable water-soluble chlorins exhibit Qy absorption/emission in water at 613/614, 636/638, 698/700 and 706/710 nm. The spectral properties are essentially unchanged in DMF and water for the facially encumbered chlorins, which also exhibit narrow Qy absorption and emission bands (full-width-at-half maximum of each <25 nm). The water-solubility was assessed by absorption spectroscopy over the concentration range ~0.4 μM – 0.4 mM. One chlorin was conjugated to a mouse polyclonal IgG antibody for use in flow cytometry with compensation beads for proof-of-principle. The conjugate displayed a sharp signal when excited by a violet laser (405 nm) with emission in the 620–660 nm range. Taken together, the designs described herein augur well for development of a set of spectrally distinct chlorins with relatively sharp bands in the red region.