Christian Brückner

DPA-substituted coumarins as chemosensors for zinc(II): modulation of the chemosensory characteristics by variation of the position of the chelate on the coumarin

The sensory capabilities of two novel di(2-picolyl)amine (DPA)-substituted coumarins are described and it is shown that the variation of the point of attachment of the DPA group to the coumarin framework controls their sensing behavior: the 4-substituted system is a CHEF-type sensor that shows a significant increase in fluorescence intensity upon Zn(2+) binding, whereas the 3-substituted system is a ratiometric sensor.

SYMMETRY-DRIVEN RATIONAL DESIGN OF A TETRAHEDRAL SUPRAMOLECULAR TI4L4 CLUSTER

General design principles for the formation of tetrahedral M4L4 clusters (L=ligand) are outlined and exemplified by the formation and structure of the [Ti4L4]8− species pictured on the right.

Squaramide hydroxamate-based chemidosimeter responding to iron(III) with a fluorescence intensity increase.

The synthesis and in vitro evaluation of a squarate hydroxamate-coumarin conjugate, 12, as a chemodosimeter for Fe(III) and other oxidants, such as Cr(VI) and Ce(IV), is described. As 12 was originally designed to become a chelation-enhanced fluorescence (CHEF)-type sensor for Fe(III), the competence of the squarate diamide platform to relay a CHEF response was demonstrated using a zinc-binding, cyclen-substituted squarate coumarin amide. Due to a photo electron transfer process, 12 possesses a low fluorescence yield. Upon exposure of 12 to Fe(III) (or other oxidants), an irreversible 9-fold fluorescence intensity increase is observed as the result of an oxidation/hydrolysis reaction. The (aminomethyl)coumarin portion of 12 is oxidized to an iminocoumarin that hydrolyzes to produce a highly fluorescent coumarinaldehyde. Fe(III) acts as a catalyst in this transformation, thereby enhancing the sensitivity of the system for the detection of Fe(III) down to 1 ppm in aqueous buffer solution. The identities of the major reaction products between 12 and Fe(III) were proven by independent synthesis.

Novel and Improved Syntheses of 5,15-Diphenylporphyrin and its Dipyrrolic Precursors

Optimized syntheses of 5,15-diphenylporphyrin (DPP, 1) and its dipyrrolic precursors are described. A novel procedure for the synthesis of dipyrromethane (2), prepared by hydrodesulfurization of the corresponding di-2-pyrrolylthione (8), is presented, as well as an improved method to isolate large quantities of 5-phenyldipyrromethane (4), prepared by the acid-catalysed condensation of pyrrole with benzaldehyde. These dipyrromethanes are key reagents in two high-yield (2a2)-type syntheses of DPP. 5-Phenyldipyrromethane was formylated to provide 1-formyl- (11) and 1,9-diformyl-5-phenyldipyrromethane (12), and reduction of 11 provided the corresponding hydroxymethyl compound 13. These compounds (11-13), however, were much less efficient precursors to DPP. Two polypyrrolic compounds, 1,1,2,2-dipyrrolylethane (9) and 5,10- diphenyltripyrrane (10), potentially useful for the synthesis of porphyrinic macrocycles, were isolated as side- products during the dipyrromethane and 5-phenyldipyrromethane syntheses. # 1998 John Wiley & Sons, Ltd.

A spectroscopic and computational study of the singlet and triplet excited states of synthetic β-functionalized chlorins

This paper presents a comparative investigation of the absorption, fluorescence, electron paramagnetic resonance (EPR), and transient triplet–triplet absorption spectroscopic properties and triplet state dynamics of two functionalized, synthetic, meso-phenylchlorins. The chromophores investigated are the novel 2-hydroxy-3-oxa-5,10,15,20-tetrakisphenylchlorin (3) and the known 2,3-dioxo-5,10,15,20-tetrakisphenylchlorin (4). In these chromophores, one peripheral ACH@CHA bond of the parent porphyrin meso-tetrakisphenylporphyrin (TPP, 1) was formally replaced by a ACH(OH)OA (lactol) or a b-diketone moiety. The spectroscopic data are compared with results from investigations on the parent porphyrin TPP studied here and the parent chlorin 5,10,15,20-tetrakisphenylchlorin (TPC, 2) from the literature. The spectroscopic observables are examined both qualitatively within the framework of the four orbital model and quantitatively using MNDO-PSDCI methods. The results delineate the role of b-lactol and b-dicarbonyl moieties in controlling the electronic and spectroscopic properties of these chromophores. This investigation serves as the foundation from which to derive a general understanding of the effects of b-functionalization on the electronic properties of chlorin-type chromophores. This knowledge is required for the design and understanding of longwavelength absorbing and fluorescing chromophores to be used in light harvesting systems and photomedicine. 2003 Elsevier B.V. All rights reserved.

meso-Tetraarylporpholactones as high pH sensors.

The ability of meso-tetra(pentafluorophenyl)porpholactone (T(F)PL) and its Pt(II) complex [meso-tetra(pentafluorophenyl)porpholactonato]Pt(II) (T(F)PLPt) to function as optical high pH sensors is described. Under strongly alkaline or high methoxide conditions, their UV-vis spectra undergo dramatic and reversible red-shifts. The dynamic range for the sensor T(F)PLPt in solution is from pH 11.5 to 13.2. Using (1)H, (19)F, and (13)C NMR, UV-vis and IR spectroscopy, mass spectrometry, and the use of model compounds, the molecular origin of this optical shift is deduced to be a nucleophilic attack of OH(-)/MeO(-) on the lactone carbonyl of the chromophore, representing a novel mechanism for porphyrin-based sensors. The sensing compound was solubilized with Cremophor EL for use in aqueous solutions and embedded in polymer matrixes for testing as optical fiber-based optodes and planar sheet optode materials.

2,3-vic-Dihydroxy-meso-tetraphenylchlorins from the osmium tetroxide oxidation of meso-tetraphenylporphyrin

Abstract meso -Tetraphenylporphyrins and meso -tetraphenylmetalloporphyrins were converted into stable 2,3- vic -dihydroxy- meso -tetraphenylchlorins and 2,3- vic -dihydroxy- meso -tetraphenylmetallochlorins by oxidation with stoichiometric amounts of OsO 4 and subsequent reduction of the isolable osmate esters. The stable dihydroxychlorins were dehydrated under acid catalysis to yield 2-hydroxy- meso -tetraphenylporphyrins.

Helimeric Porphyrinoids: Stereostructure and Chiral Resolution of meso-Tetraarylmorpholinochlorins

The synthesis and chiral resolution of free-base and Ni(II) complexes of a number of derivatives of meso-tetraphenylmorpholinochlorins, with and without direct β-carbon-to-o-phenyl linkages to the flanking phenyl groups, is described. The morpholinochlorins, a class of stable chlorin analogues, were synthesized in two to three steps from meso-tetraphenylporphyrin. The conformations and the relative stereostructures of a variety of free-base and Ni(II) complexes of these morpholinochlorins were elucidated by X-ray diffractometry. Steric and stereoelectronic arguments explain the relative stereoarray of the morpholino-substituents, which differ in the free-base and Ni(II) complexes, and in the monoalkoxy, β-carbon-to-o-phenyl linked morpholinochlorins, and the dialkoxy derivatives. The Ni(II) complexes were all found to be severely ruffled whereas the free-base chromophores are more planar. As a result of the helimeric distortion of their porphyrinoid chromophores, the ruffled macrocycles possess a stable inherent element of chirality. Most significantly, resolution of the racemic mixtures was achieved, both by classical methods via diastereomers and by HPLC on a chiral phase. Full CD spectra were recorded and modeled using quantum-chemical computational methods, permitting, for the first time, an assignment of the absolute configurations of the chromophores. The report expands the range of known pyrrole-modified porphyrins. Beyond this, it introduces large chiral porphyrinoid π-systems that exist in the form of two enantiomeric, stereochemically stable helimers that can be resolved. This forms the basis for possible future applications, for example, in molecular-recognition systems or in materials with chiroptic properties.

SYMMETRIEGESTEUERTES RATIONALES DESIGN EINES TETRAEDRISCHEN SUPRAMOLEKULAREN TI4L4-CLUSTERS

Allgemeingultige Prinzipien fur das Design von tetraedrischen M4L4-Clustern (L=Ligand) werden am Beispiel der Bildung und Struktur der rechts abgebildeten [Ti4L4]8−-Spezies naher erlautert.

meso-Arylporpholactones and their Reduction Products

The rational syntheses of meso-tetraaryl-3-oxo-2-oxaporphyrins 5, known as porpholactones, via MnO(4)(-)-mediated oxidations of the corresponding meso-tetraaryl-2,3-dihydroxychlorins (7) is detailed. Since chlorin 7 is prepared from the parent porphyrin 1, this amounts to a 2-step replacement of a pyrrole moiety in 1 by an oxazolone moiety. The stepwise reduction of the porpholactone 5 results in the formation of chlorin analogues, meso-tetraaryl-3-hydroxy-2-oxachlorin (11) and meso-tetraaryl-2-oxachlorins (12). The reactivity of 11 with respect to nucleophilic substitution by O-, N-, and S-nucleophiles is described. The profound photophysical consequences of the formal replacement of a pyrrole with an oxazolone (porphyrin-like chromophore) or (substituted) oxazole moiety (chlorin-like chromophore with, for the parent oxazolochlorin 12, red-shifted Q(x) band with enhanced oscillator strengths) are detailed and rationalized on the basis of SAC-CI and MNDO-PSDCI molecular orbital theory calculations. The single crystal X-ray structures of the porpholactones point at a minor steric interaction between the carbonyl oxygen and the flanking phenyl group. The essentially planar structures of all chromophores in all oxidation states prove that the observed optical properties originate from the intrinsic electronic properties of the chromophores and are not subject to conformational modulation.