A Two-Dimensional Poly(azatriangulene) Covalent Organic Framework with Semiconducting and Paramagnetic States.

The black crystalline (aza)triangulene-based covalent organic framework TANG-COF was synthesized from its trinitro-TANG precursor via a one-pot, two-step reaction involving Pd-catalyzed hydrogenation and polycondensation with an aromatic dialdehyde. High crystallinity and permanent porosity of the layered two-dimensional (2D) structure were established. The rigid, electron-rich trioxaazatriangulene (TANG) building block enables strong π-electron interactions manifested in broad absorptions across the visible and NIR regions (Eg ≈ 1.2 eV). The high HOMO energy of TANG-COF (-4.8 eV) enables facile p doping, resulting in electrical conductivity of up to 10-2 S/cm and room-temperature paramagnetic behavior with a spin concentration of ∼10%. DFT calculations reveal dispersion of the highest occupied band both within the 2D polymer layers (0.28 eV) and along their π-stacked direction (0.95 eV).

Halogenated boron-dipyrromethenes: synthesis, properties and applications.

Boron-dipyrromethene dyes (BODIPYs) containing halogens at pyrrole carbons are very useful synthons for the synthesis of a variety of BOIDPYs for a wide range of applications. Among the functional groups, halogens are the functional groups which can be regiospecifically introduced at any desired pyrrole carbon of the BODIPY framework by adopting appropriate synthetic strategies. The halogenated BODIPYs can undergo facile nucleophilic substitution reactions to prepare several interesting BODIPY based compounds. This review describes the synthesis, properties and potential applications of halogenated BODIPYs containing one to six halogens at the pyrrole carbons of the BODIPY core as well as properties and applications of some of the substituted BODIPYs derived from halogenated BODIPYs.

Synthesis of conjugated BODIPYs via the Wittig reaction.

A Wittig reaction was employed to synthesize conjugated BODIPYs in high yields by treating formylated BODIPYs with alkyl/aryl ylides under simple room temperature conditions. Treatment of 3,5-diformyl BODIPYs or α-formyl 3-pyrrolyl BODIPY with different alkyl/aryl ylides in CH2Cl2 at room temperature for 2 h followed by straightforward column chromatographic purification on silica afforded conjugated BODIPYs in ~65-90% yields. This is an alternate method to Knoevenagel and Heck reactions which have been used to synthesize such conjugated BODIPYs. The method works very efficiently, and we prepared 12 substituted BODIPYs including cholesterol-substituted BODIPYs to demonstrate the versatility of the reaction. The spectral, electrochemical, and fluorescence properties of these conjugated BODIPYs are also described.

Synthesis and properties of meso-unsubstituted 3-pyrrolyl boron dipyrromethene.

We report the synthesis of meso-free 3-pyrrolyl boron dipyrrin (3-pyrrolyl BODIPY) and fully unsubstituted meso-free boron dipyrrin (parent BODIPY) in one pot under simple reaction conditions by treating meso-free dipyrromethane with pyrrole in CHCl3 followed by oxidation with DDQ, neutralization with triethylamine and complexation with BF3.OEt2. The compounds were separated by column chromatography on silica and isolated in 6-10 % yields. The compounds are characterized by HR-MS mass, NMR, absorption, electrochemical and fluorescence techniques. The meso-free 3-pyrrolyl BODIPY exhibit red shifted absorption and emission bands compared to meso-free BODIPY. The meso-free BODIPY exhibit green fluorescence and meso-free 3-pyrrolyl BODIPY exhibit orange fluorescence in solution. Furthermore, compared to meso-phenyl 3-pyrrolyl BODIPY, the meso-free 3-pyrrolyl BODIPY is more strongly fluorescent with nearly 41 % increase in quantum yield. Electrochemical studies showed that meso-free 3-pyrrolyl BODIPY exhibit one irreversible reduction and one ill-defined oxidation indicating that the compound is not stable under redox conditions. Computational studies revealed that meso-free pyrrolyl BODIPY has reduced HOMO-LUMO gap compared to parent meso-free BODIPY. Furthermore, the meso-free 3-pyrrolyl BODIPY exhibit much higher quantum yield compared to meso-aryl analogue of 3-pyrrolyl BODIPY.

A croconic acid-derived narrow band gap conjugated microporous polymer.

Croconic acid, a novel highly electron-deficient building block, was introduced into a conjugated microporous polymer (CTPA). The CMP possesses strong donor-acceptor interactions, which resulted in near-IR absorption (red edge ∼1350 nm), a narrow bandgap (<1 eV) and high electrical conductivity upon doping (0.1 S m-1). Compared to the squaric acid congener (STPA), CTPA showed superior optical, electronic and electrical properties.

Synthesis of sterically crowded polyarylated boron-dipyrromethenes.

A rapid synthetic route for polyarylated boron-dipyrromethenes using hexabromo boron-dipyrromethene as the key synthon is described. The X-ray structure revealed that the polyarylated BODIPY adopts a propeller-like conformation. These compounds exhibit red-shifted absorption and fluorescence bands with decent quantum yields and reversible oxidation and reduction waves when compared to unsubstituted boron-dipyrromethenes.

Dimension-controlled assemblies of anion-responsive π-electronic systems bearing aryl substituents with fan-shaped geometries.

Pyrrole-4-aryl-substituted dipyrrolyldiketone BF2 complexes as anion-responsive π-electronic molecules were synthesized via a 3,5-dimethylpyrrole precursor. Mesophases were observed in derivatives that possessed long alkyl chains on the pyrrole-4-aryl groups along with their anion complexes as ion-pairing assemblies in combination with appropriate cations.

Axially bonded pentads constructed on the Sn(IV) porphyrin scaffold.

Three covalently linked dyads such as porphyrin-ferrocene, porphyrin-BODIPY and porphyrin-sapphyrin containing one hydroxyphenyl group at the meso-position of porphyrin were synthesized by coupling the trans-functionalized porphyrin building block, 5-(4-hydroxyphenyl)-10-(4-iodophenyl)-15,20-diphenyl porphyrin, with the ethynyl functionalized redox/chromophore building block under mild Pd(0) coupling conditions. The dyads were then reacted with SnTTP(OH)2 in benzene in a 2 : 1 ratio at reflux temperature for 12 hours followed by simple alumina column chromatographic purification which afforded three pentads containing three different types of redox/chromophore components in 62-80% yields. The pentads are very stable and freely soluble in all common organic solvents. The pentads formation were confirmed by MALDI-TOF mass spectrometry and 1D and 2D NMR studies. Absorption and electrochemical studies suggested that the three components in pentads retain their independent characteristic features without significant alterations in their properties thus acting like supramolecular assemblies. The steady state fluorescence studies indicated a possibility of energy/electron transfer among the three types of components in pentads.