Reaction of porphyrin-based surface-anchored metal-organic frameworks to prolonged illumination

Crystalline surface-anchored metal–organic framework (SURMOF) thin films made from porphyrin-based organic linkers have recently been used in both photon upconversion and photovoltaic applications. While these studies showed promising results, the question of photostability in this organic–inorganic hybrid material has to be investigated before applications can be considered. Here, we combine steady-state photoluminescence, transient absorption, and time-resolved electron paramagnetic resonance spectroscopy to examine the effects of prolonged illumination on a palladium-porphyrin based SURMOF thin film. We find that phototreatment leads to a change in the material\u27s photoresponse caused by the creation of stable products of photodecomposition – likely chlorin – inside the SURMOF structure. When the mobile triplet excitons encounter such a defect site, a short-lived (80 ns) cation–anion radical pair can be formed by electron transfer, wherein the charges are localized at a porphyrin and the photoproduct site, respectively

Facile synthesis of 9,10,19,20-tetraarylporphycenes

A simple route was developed for the synthesis of 9,10,19,20-tetraarylporphycenes by combining both McMurry and oxidative synthetic strategies and using readily available precursors. The desired 5,6-diaryldipyrroethenes, which were prepared in multigram quantities over two steps, were used to prepare 9,10,19,20-tetraarylporphycenes under mild acid-catalyzed conditions. As 5,6-diaryldipyrroethene precursors can easily be prepared in multigram quantities, this method is useful for the preparation of meso-tetrarylporphycenes that contain different aryl substituents. The molecular structures of these macrocycles were determined by HRMS analysis as well as 1D and 2D NMR studies. The tetraarylporphycenes exhibited a strong Soret band at approximately 380 nm and three Q bands in the region of 580–655 nm. The tetraarylprophycenes are reasonably fluorescent and stable under redox conditions

Crystal structure and synthesis of 3-(1H-pyrrol-2-yl)-1-(thiophen-2-yl)propanone

The title compound, C11H9NOS, was obtained in an improved yield compared to previous literature methods. The molecule is essentially planar with a maximum deviation of 0.085 Å from the mean plane through all non-H atoms. There is directive intermolecular hydrogen bonding in the form of N—H...O hydrogen bonds with a distance of 2.889 (3) Å between the pyrrole amine and the ketone carbonyl O atom. The resulting hydrogen-bonding network defines a ribbon parallel to the a axis. These ribbons form offset stacks along the b axis

Synthesis, structure and spectral and electrochemical properties of meso-tetraaryl-27-thiasapphyrins

An alternate synthetic route was developed for tetraaryl 27-thiasapphyrins by condensation of meso-aryl dipyrromethanes with 2,5-bis(p-tolylhydroxymethyl)thiophene under acid-catalyzed conditions. Previously, 27-thiasapphyrins have been prepared by a multistep synthesis using 2,2′-bipyrrole as the key precursor. In our strategy, the pyrrole–pyrrole bond was generated to form 27-thiasapphyrins by oxidative coupling of meso-aryl dipyrromethane and 2,5-bis(p-tolylhydroxymethyl)thiophene, and the desired 27-thiasapphyrins were isolated in 8–12 % yields. The crystal structure of one of the 27-thiasapphyrins indicates that the macrocycle is almost planar and the thiophene sulfur atom is in the plane whereas the four pyrrole nitrogen atoms slightly deviate from the plane defined by four meso carbon atoms. Absorption spectroscopy showed four well defined Q bands in 590–770 nm and one strong Soret band in 470–480 nm region for 27-thiasapphyrins. The 27-thiasapphyrins are stable under redox conditions and undergo two-to-three reversible oxidations and one-to-two reversible reductions. The macrocycles are weakly fluorescent with low quantum yields and singlet state lifetimes

Synthesis, structure and properties of core-modified pentaphyrins containing six meso carbons

Our successful synthesis of nonaromatic 24π core-modified pentaphyrins containing six meso carbons is reported. The pentaphyrins were prepared by [3+2] condensation of butane-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl tripyrromethanes under mild acid-catalyzed conditions. By using this method, we obtained two stable, core-modified pentaphyrins containing six meso carbons in acceptable yields. The pentaphyrins were characterized by HR-MS, 1D, 2D NMR, absorption and electrochemical techniques and also by X-ray crystallography for one of the pentaphyrin macrocycles. The crystal structure revealed that the macrocycle is almost planar and one of the thiophene rings, which is positioned opposite to the ethene bridged meso-carbons, is inverted. Our studies revealed that the macrocycles in their protonated form have specific sensing ability for CH3COO− ions

Stable Nonaromatic [20]Dithiaporphyrin (2.1.1.1) Macrocycles: Synthesis, Structure, Spectral, Electrochemical, and Metal Ion Sensing Studies

Stable nonaromatic [20]­dithiaporphyrin (2.1.1.1) macrocycles were synthesized in decent yields by condensing readily available butene-2,3-diyl-bisthiophene-2,5-diyl-bis­(<i>p</i>-methoxyphenylmethanol) with different <i>meso</i>-aryl dipyrromethanes under mild acid-catalyzed conditions. The [20]­dithiaporphyrin (2.1.1.1) macrocycles are the first members of the expanded porphyrin analogues of [18]­dithiaporphyrin (1.1.1.1) and consist of two pyrroles and two thiophenes connected through five <i>meso</i>-carbon bridges. The [20]­dithiaporphyrin macrocycles were confirmed by mass spectroscopy, 1D and 2D NMR spectroscopy, and X-ray crystallography. The X-ray structure revealed that the macrocycle is highly distorted and that the two thiophene rings are completely out-of-plane from the “mean-plane” defined by the dipyrromethene moiety and the two <i>meso</i>-carbons. In the absorption spectrum, the macrocycles showed one strong band at ∼420 nm and one weak band at ∼720 nm. The electrochemical studies revealed that the macrocycles are stable under redox conditions. The metal sensing studies indicated that these macrocycles have the potential to sense specific metal ions such as Hg²⁺ ions. Two covalently linked dithiahomoporphyrin–fluorophore dyads were synthesized by coupling iodo-functionalized dithiahomoporphyrin with an ethynyl-functionalized fluorophore such as boron–dipyrromethene (BODIPY) and BF₂–smaragdyrin under mild Pd(0) coupling conditions. The potential of these dyads as a fluorescent sensor for Hg²⁺ was explored, and the studies indicated that both dyads can be used as fluorescent sensors

Mixed boron(III) and phosphorous(V) complexes of meso-triaryl 25-oxasmaragdyrins

Two unprecedented mixed BIII/PV complexes of meso-triaryl 25-oxasmaragdyrins were synthesized in appreciable yields under mild reaction conditions. These unusual 25-oxasmaragdyrin complexes containing one or two seven-membered heterocyclic rings comprised of five different atoms (B, C, N, O and P) were prepared by reacting B(OH)(Ph)-smaragdyrin and B(OH)2-smaragdyrin complexes, respectively, with POCl3 in toluene at reflux temperature. The products were characterized by HRMS and 1D- and 2D-NMR spectroscopy. X-ray crystallography of one of the mixed BIII/PV smaragdyrin complexes indicated that the macrocycle is significantly distorted and contains a stable seven-membered heterocyclic ring within the macrocycle. The bands in the absorption and emission spectra were bathochromically shifted with reduced quantum yields and singlet-state lifetimes relative to the free base, meso-triaryl 25-oxasmaragdyrin. The mixed BIII/PV complexes were difficult to oxidize but easier to reduce than the free base. The DFT-optimized structure of the 25-oxasmaragdyrin complex with two seven-membered heterocycles indicated that it was a bicyclic spiro compound with two half-chair-like conformers. This was in contrast to the chair-like conformation of the complex with a single seven-membered heterocyclic ring. Moreover, incorporation of a second phosphate group in the former case stabilized the bonding geometry and resulted in higher stability, which was reflected in the bathochromic shift of the absorption spectra, more-positive oxidation potential and less-negative reduction potential

Water-soluble, neutral 3,5-diformyl-BODIPY with extended fluorescence lifetime in a self-healable chitosan hydrogel

3,5-Diformyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (3,5-diformyl-BODIPY) can be used as an efficient biofunctional cross-linker to generate a new class of chitosan-based hydrogels with fluorescence resonance energy transfer (FRET) dynamics and good solubility in water. The hydrogel was fully characterized by FT-IR, UV-vis, fluorescence, FE-SEM, AFM, rheology and picosecond time-resolved spectroscopic techniques. The self-healing ability was demonstrated by rheological recovery and macroscopic and microscopic observations. The fluorescence lifetime was found to increase in aqueous solution of the BODIPY-chitosan hydrogel compared to the 3,5-diformyl-BODIPY monomer. Calculations based on experimental results such as red-shift and decreased intensity of the emission spectrum of highly dye-concentrated hydrogel in comparison to dilute hydrogels, together with changes in the fluorescence lifetime of the hydrogel at different concentration of dyes, suggest that the BDP-CS hydrogels fluorescence dynamics obey the F?rster resonance energy transfer (FRET). Improvements in mechanical and photochemical properties and the acceptable values of BODIPY fluorescence lifetime in the hydrogel matrix indicate the utility of the newly synthesized hydrogels for biomedical applications