Synthesis of mono meso-pyridyl 21,23-dithiaporphyrins and unsymmetrical non-covalent dimers

A new method has been developed to synthesize 21,23-dithiaporphyrins having one pyridyl group at the meso position. The method required easily available unknown precursors and the condensation resulted in mono meso-pyridyl 21,23-dithiaporphyrins as single products in 8–11 % yield. Two of the three mono meso-pyridyl N₂S₂ porphyrins were used to synthesize non-covalent unsymmetrical porphyrin dimers containing one N₂S₂ and one N₄ porphyrin cores

Synthesis of functionalized unsymmetrical thiophene diols and their use in the synthesis of cis-21-monothia- and cis-21,23-dithiaporphyrin building blocks with two different functional groups

A series of functionalized unsymmetrical thiophene diols were synthesized and used for the synthesis of cis-21-monothia and cis-21,23-dithiaporhhyrin building blocks having two different functional groups at meso-positions. To show the use of the cis-thiaporphyrin building blocks with two different functional groups, a porphyrin trimer comprised of N₄, N₃S and N₂S₂ porphyrin sub-units was synthesized by using both covalent and noncovalent interactions

2-Formyl boron-dipyrromethene as a key synthon to prepare functionalized meso-boron dipyrromethenyl porphyrin building blocks

A series of functionalized meso-boron dipyrromethenyl porphyrin building blocks were synthesized by condensing one equivalent of readily available 2-formyl boron dipyrromethene (2-formyl BODIPY) with two equivalents of meso-anisyl dipyrromethane and one equivalent of functionalized aldehyde under mild acid catalyzed conditions followed by column chromatographic purification and afforded in 5–7 % yields. The meso-BODIPYnyl porphyrins are freely soluble in common organic solvents and characterized by mass, spectral and electrochemical techniques. The presence of a BODIPY unit directly at the meso-position alters the π-delocalization of the porphyrin macrocycle. The compounds are weakly fluorescent because of effective charge transfer between the porphyrin and BODIPY units leading to the formation of a low lying charge transfer state. The meso-BODIPYnyl porphyrin–BF₂–smaragdyrin conjugate was synthesized by coupling a meso-BODIPYnyl porphyrin building block containing a meso-iodophenyl group with ethynyl BF₂–smaragdyrin under Pd(0) coupling conditions. The spectral and electrochemical studies indicated that the photo-induced electron transfer is the predominant process in the meso-BODIPYnyl porphyrin–₂–smaragdyrin conjugate

Synthesis of hexasubstituted boron-dipyrromethenes having a different combination of substituents

A series of sterically crowded, mixed hexasubstituted BODIPYs containing two different types of substituents on the pyrrole carbons have been synthesized in high yields by a stepwise approach. The mixed BODIPYs were synthesized by bromination of BODIPYs followed by coupling with appropriate boronic acids under Suzuki coupling conditions. This approach has allowed the introduction of two different types of methyl/aryl substituents at the designated positions of the BODIPY core. All the hexasubstituted BODIPYs are readily soluble in common organic solvents and have been characterized by various spectral and electrochemical techniques. The spectral studies indicated that the presence of mixed methyl/aryl substituents on the BODIPY core significantly alters the electronic properties, and the electrochemical studies revealed that the BODIPYs are stable under redox conditions

Synthesis and studies of covalently linked BF₂-oxasmaragdyrin-BODIPY and BF₂-oxasmaragdyrin-ferrocene dyads

Covalently linked BF₂-oxasmaragdyrin-BODIPY and BF₂-oxasmaragdyrin-ferrocene dyads were synthesized by coupling of meso-triaryl oxasmaragdyrin containing meso-iodophenyl group with meso-(p-ethynylphenyl) borondipyrromethene and α-ethynyl ferrocene respectively under mild Pd(0) coupling conditions. NMR, absorption and electrochemical studies indicated that the two moieties in the dyads retain their individual characteristic features. The fluorescence studies indicated a possibility of photoinduced singlet-singlet energy transfer from BODIPY unit to BF₂-oxasmaragdyrin unit in BF₂-oxasmaragdyrin-BODIPY dyad and photoinduced electron transfer from ferrocene unit to excited state of BF₂-oxasmaragdyrin unit in BF₂-oxasmaragdyrin-ferrocene dyad

Meso-pyrrole-substituted 22-oxacorroles: building blocks for the synthesis of bodipy-bridged 22-oxacorrole dyads

Novel boron-dipyrromethene (BODIPY)-bridged 22-oxacorrole dyads, using meso-pyrrolyl 22-oxacorrole as a key synthon, have been synthesized. The reactivity of the meso-pyrrolyl group of 22-oxacorrole was exploited to synthesize the first examples of BODIPY-bridged 22-oxacorrole dyads in ≈40% yield. The dyads are stable and exhibited interesting spectral and electrochemical properties

Multiporphyrin assemblies on cyclophosphazene scaffolds: synthesis and studies

The stable and robust cyclotriphosphazene and cyclotetraphosphazene rings were used as scaffolds to prepare hexa- and octaporphyrin arrays by treating N3P3Cl6 and N4 P4 Cl8, respectively, with 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl)porphyrin (N4 core) or with its thiaporphyrin analogues (N3S and N2S2 cores) in THF in the presence of Cs2CO3 under simple reaction conditions. Thiaporphyrins were examined in addition to the normal porphyrin to tune the electronic properties of the resultant arrays. Observation of the molecular ion peaks in the mass spectra confirmed the molecular structures of the arrays. 1D and 2D NMR techniques were employed to characterize the multiporphyrin arrays in detail. The 1H NMR spectra of the multiporphyrin arrays each show a systematic set of signals, indicating that the porphyrin units are arranged in a symmetrical fashion around the cyclophosphazene rings. All signals in the 1H NMR spectra were assigned with the aid of COSY and NOESY experiments. The protons of each porphyrin unit are subject to upfield and downfield shifts because of the ring-current effects of neighboring porphyrin units. Optical, electrochemical and fluorescence studies of the arrays indicated that the porphyrin units retain their independent ground- and excited-state characteristics. CuII and NiII derivatives of hexaporphyrin and octaporphyrin arrays containing N4 porphyrin units and N3 S porphyrin units were synthesized, and complete metalation of the arrays was confirmed by their mass spectra and by detailed NMR characterization of the NiII derivatives of hexa- and octaporphyrin arrays containing N4 porphyrin units. Electrochemical studies indicated that CuII and NiII ions present in the thiaporphyrin units of the arrays can be stabilized in the +1 oxidation state, which is not possible with arrays containing normal porphyrin units

Boron-Dipyrromethene Based Reversible and Reusable Selective Chemosensor for Fluoride Detection

We synthesized benzimidazole substituted boron-dipyrromethene <b>1</b> (BODIPY <b>1</b>) by treating 3,5-diformyl BODIPY <b>2</b> with <i>o</i>-phenylenediamine under mild acid catalyzed conditions and characterized by using various spectroscopic techniques. The X-ray structure analysis revealed that the benzimidazole NH group is involved in intramolecular hydrogen bonding with fluoride atoms which resulted in a coplanar geometry between BODIPY and benzimidazole moiety. The presence of benzimidazole moiety at 3-position of BODIPY siginificantly altered the electronic properties, which is clearly evident in bathochromic shifts of absorption and fluorescence bands, improved quantum yields, increased lifetimes compared to BODIPY <b>2</b>. The anion binding studies indicated that BODIPY <b>1</b> showed remarkable selectivity and specificity toward F^– ion over other anions. Addition of F^– ion to BODIPY <b>1</b> resulted in quenching of fluorescence accompanied by a visual detectable color change from fluorescent pink to nonfluorescent blue. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bonding between BODIPY and benzimidazole moieties leading to (i) noncoplanar geometry between BODIPY and benzimidazole units and (ii) operation of photoinduced electron transfer (PET) from benzimidazole moiety to BODIPY unit causing quenching of fluorescence. Interestingly, when we titrated the nonfluorescent blue <b>1-F</b>^– solution with TFA resulted in a significant enhancement of fluorescence intensity (15-fold) because the PET quenching is prevented due to protonation of benzimidazole group. Furthermore, the reversibility and reusability of sensor <b>1</b> for the detection of F^– ion was tested for six cycles indicating the sensor <b>1</b> is stable and can be used in reversible manner

Synthesis and properties of covalently linked trichromophore systems

Four covalently linked trichromophore systems containing a central boron dipyrromethene (BODIPY) unit connected to a porphyrin unit through the 3-position and a core-modified porphyrin or a porphyrin expanded through the 5-position were synthesized by treating 3-bromo-5-porphyrinyl BODIPY or 3-bromo-5-rubyrinyl BODIPY with the corresponding hydroxy porphyrin or hydroxy-expanded porphyrin in CHCl3 at 60°C. The compounds are freely soluble in common organic solvents and confirmed by mass spectrometry and 1D and 2D NMR spectroscopy techniques. The absorption and electrochemical studies support weak ground-state interactions among the three chromophore units within the trichromophore systems. The fluorescence studies indicate that BODIPY emission is quenched to a significant degree in all trichromophore systems due to a transfer of energy to one or both macrocyclic units attached to the BODIPY chromophore