Synthetic Exploration of Bis(phenolate) Aza-BODIPYs and Heavier Group 13 Chelates.

A series of boron, aluminum, gallium, and indium chelates containing the underexplored bis(phenolate) aza-dipyrromethene (aza-DIPY) core were prepared. These compounds were found to possess near-infrared absorption and emission profiles in the 710 to 770 nm domain and exhibit quantum yield values up to 14%. X-ray diffraction analysis revealed that heavier group 13 bis(phenolate) aza-DIPY chelates possessed octahedral geometries with either THF or pyridine groups occupying the axial positions as opposed to the tetrahedral geometry of the boron chelate.

Donor-/Acceptor-Substituted Tetrakis(arylethynyl)benzenes: The Influence of Donor Group on Optoelectronic Properties.

We have prepared nine structural isomers of a tetrakis(arylethynyl)benzene chromophore functionalized with 4-butoxyphenyl and pyridyl units as the respective donor and acceptor units and examined their steady-state spectroscopic parameters to study how small structural variations effect the electronic absorption and emission spectra. Unlike their 4-dibutylaminophenyl congeners that exhibited dynamic hypsochromic or bathochromic shifts in response to Lewis and Brønsted acids, the current class of compounds simply showed quenched fluorescence upon protonation; only AlCl3 elicited a red-shifted fluorescence response. Computational studies of each system were also performed to provide additional insight into the energy levels and electronic transitions present.

Crystal structures of two unusual, high oxidation state, 16-electron irida-benzenes.

Treatment of carbon-yl(1,2-diphenylpenta-1,3-dien-1-yl-5-yl-idene)bis-(tri-phenyl-phosphane)iridium, [IrCO(-C(Ph)=C(Ph)-CH=CH-CH=)(PPh3)2], with either bromine or iodine produced di-bromido-(1,2-diphenylpenta-1,3-dien-1-yl-5-yl-idene)(tri-phenyl-phosphine)iridium(III), [IrBr2{-C(Ph)=C(Ph)-CH=CH-CH=}(PPh3)], (I), and (1,2-diphenylpenta-1,3-dien-1-yl-5-yl-idene)di-iodido-(tri-phenyl-phosphane)iridium(III), [IrI2{-C(Ph)=C(Ph)-CH=CH-CH=}(PPh3)], (II), respectively, which are two rare examples of 16-electron metalla-benzenes. Structural elucidation of (I) and (II) reveals that these isotypic irida-benzenes are unusual, not only in their electron count, but also in their coordination sphere of the Ir(III) atom where they contain an apparent open coordination site. The crystal structures of (I) and (II) confirm that the mol-ecules are complexes containing five-coordinated Ir(III) with only one tri-phenyl-phosphine group bound to the iridium atom, unambiguously proving that the mol-ecules are indeed 16-electron, high-oxidation-state irida-benzenes. The coordination geometry of the Ir(III) atom in both structures can be best described as a distorted square pyramid with the P, two Br (or I) and one C atom in the basal plane and another C atom in the apical position.

Synthesis and Properties of Fully-Conjugated Indacenedithiophenes.

The synthesis and characterization of four fully-conjugated indacenedithiophenes (IDTs) are disclosed. In contrast to anthradithiophenes, regioselective synthesis of both syn and anti isomers is readily achieved. Thiophene fusion imparts increased paratropic character on the central indacene core as predicted by DFT calculations and confirmed by 1H NMR spectroscopy. IDTs exhibit red-shifted absorbance maxima with respect to their all-carbon analogues and undergo two-electron reduction and one-electron oxidation.

Exploring the chemistry of N,N'-diamidocarbenes with organophosphorus compounds.

A readily available N,N'-diamidocarbene (DAC) was found to insert into the P-H bonds of primary and secondary phosphines as well as a phosphonate ester. In contrast, tertiary phosphines catalyzed the ring contraction of the DAC to an iminopyrrolidinedione. Treating the DAC with trimethyl phosphite afforded the corresponding diamidophosphonate ester and olefinic products expected from an Arbuzov-type reaction.

Indenofluorenes and derivatives: syntheses and emerging materials applications.

The growing demand for flexible electronic devices and hydrogen storage materials has spurred a resurgence of interest in polyaryl hydrocarbons including graphene, acenes, fullerenes, polythiophenes, etc. Indenofluorenes are another polyaryl molecular scaffold that has shown utility in the organic and hybrid materials arena, with polymers incorporating the indeno[1,2-b]fluorene moiety being common in organic light emitting diodes. This review examines the syntheses and properties of the five distinct indenofluorene regioisomers, with a focus on small molecule applications in organic electronics of this intriguing and somewhat underexplored family of polyaryl hydrocarbons.

Elucidation of carbene ambiphilicity leading to the discovery of reversible ammonia activation.

An N,N'-diamidocarbene (DAC) was found to activate a broad range of primary as well as secondary aliphatic and aromatic amines. The relative rates measured for the insertion of the DAC into the primary amines were consistent with an electrophilic activation mechanism; in contrast, the DAC functioned as a nucleophile upon treatment with secondary aryl amines. Collectively, these results constituted the first ambiphilic process for an isolable carbene. By comparison, an analogous diaminocarbene was found to serve exclusively as a nucleophile under similar conditions and led to the discovery of the first organic reagent to reversibly activate ammonia.

Elucidating the mechanism of reversible oxiranations via magnetization transfer spectroscopy.

The reversible [2 + 1] cycloadditions between an N,N'-diamidocarbene (DAC) and eight aldehydes were examined using NMR spectroscopy. Variable temperature magnetization transfer experiments revealed higher exchange rates and lower activation barriers when electron-deficient aldehydes were employed. Likewise, competitive equilibrium studies indicated a thermodynamic preference for electron-deficient aryl and sterically unhindered alkyl aldehydes compared to more electron-rich or bulkier substrates. Collectively, these and other data collected were consistent with the oxiranation process proceeding in an asynchronous manner.

6,12-Diarylindeno[1,2-b]fluorenes: syntheses, photophysics, and ambipolar OFETs.

Herein we report the synthesis and characterization of a series of 6,12-diarylindeno[1,2-b]fluorenes (IFs). Functionalization with electron donor and acceptor groups influences the ability of the IF scaffold to undergo two-electron oxidation and reduction to yield the corresponding 18- and 22-π-electron species, respectively. A single crystal of the pentafluorophenyl-substituted IF can serve as an active layer in an organic field-effect transistor (OFET). The important finding is that the single-crystal OFET yields an ambipolar device that is able to transport holes and electrons.

Incorporating BODIPY fluorophores into tetrakis(arylethynyl)benzenes.

Six structural isomers of a tetrakis(arylethynyl)benzene (TAEB) chromophore functionalized with dibutylamine and BODIPY moieties as the corresponding donor and acceptor units were prepared. To evaluate the effectiveness of the donor group, two TAEB molecules and three structurally related bis(arylethynyl)benzene (BAEB) isomers containing only acceptors were also synthesized. The electronic absorption and emission spectra of each series were examined. Additionally, computational studies were employed to corroborate the relative energy levels and gaps present in each series.

Synthesis, crystal structures, and photophysical properties of electron-accepting diethynylindenofluorenediones.

A series of 6,12-bis[(trialkylsilyl)ethynyl]indeno[1,2-b]fluorene-5,11-diones has been synthesized. X-ray crystallographic analysis of these compounds reveals that triisopropylsilyl (TIPS) substitution on the alkyne terminus affords the largest number of intermolecular π-π interactions in the solid state. Conversely, use of trialkylsilyl groups smaller or larger than TIPS furnishes a variety of crystal-packing motifs that contain fewer π-π interactions. Electrochemical and photophysical data suggest that these molecules are excellent electron-accepting materials.