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Phlorins bearing different substituents at the sp(3)-hybridized meso-position were investigated. The extent to which different substituents at this unique position can influence phlorin spectroscopic properties, structure, and stability is of interest given that such substituents are not in direct conjugation with the phlorin macrocycle. While the effect of various substituents at the sp(2)-hybridized positions has been the subject of prior investigations, the impact of different substituents at the saturated carbon atom has not been systematically examined. In this study, phlorins with different combinations of geminal methyl and phenyl substituents were prepared in yields of 24-49% via dipyrromethane + dipyrromethanedicarbinol routes, and their NMR spectra, UV-vis spectra, X-ray crystal structures, and stability toward light and air were compared. The nature of the substituents at the sp(3)-hybridized position was found to impact spectroscopic properties, structure, and stability to varying degrees. Thus, the choice of substituents at the sp(3)-hybridized meso-position provides a further option for altering phlorin properties.

The formal replacement of one or two pyrrole groups in meso-tetraphenylporphyrin by oxazole moieties is described, generating inter alia the bacteriochlorin-type chromophores oxazolobacteriochlorins (oxabacteriochlorins) and bisoxazolobacteriochlorins (dioxabacteriochlorins). The key step is the conversion of a β,β'-dihydroxy-functionalized pyrroline group into an oxazolone or (substituted) oxazole. Depending on the substitution pattern on the oxazole or oxazoline moieties, mono- and dioxabacteriochlorins may have chlorin- or bacteriochlorin-like spectra. The optical properties (as measured by UV-vis and fluorescence spectroscopies) of the novel oxa- and dioxabacteriochlorins are described and contrasted against benchmark chlorins and bacteriochlorins. The conformations of a representative number of mono- and dioxabacteriochlorins, as their free bases or ZnII complexes, were determined by single-crystal X-ray diffractometry. They proved to be essentially planar, showing that the modulation of their optical properties is primarily due to their intrinsic electronic structures and electronic substituent effects and are not largely affected by conformational effects. The mono- and bisoxazolobacteriochlorins are a novel class of readily prepared and oxidatively stable chlorin and bacteriochlorin analogues with tunable optical spectra that, in part, reach into the NIR. [ABSTRACT FROM AUTHOR]

The formal replacement of a pyrrole moiety of meso-tetraarylporphyrin 1 by an oxazole moiety is described. The key step is the conversion of porpholactones 4 (prepared by a known two-step oxidation procedure from 1) by addition of alkyl Grignard reagent to form meso-tetraaryl-3-alkyl-2-oxachlorins 9 (alkyloxazolochlorins; alkyl = Me, Et, iPr). Hemiacetal 9 can be converted to an acetal, reduced to an ether, or converted to bis-alkyloxazolochlorins 11. The optical properties (UV-visible and fluorescence spectroscopy) are described. The chlorin-like optical properties of the alkyloxazolochlorins are compared to regular chlorins, such as 2,3-dihydroxychlorins and nonalkylated oxazolochlorins made by reduction from porpholactone 4. The conformations of the mono- and bis-alkylated 2-oxachlorins, as determined by single crystal X-ray diffractometry, are essentially planar, thus proving that their optical properties are largely due to their intrinsic electronic properties and not affected by conformational effects. The mono- and bis-3-alkyl-2-oxachlorins are a class of readily prepared and oxidatively stable chlorins. [ABSTRACT FROM AUTHOR]