Organic Photosensitizers Incorporating Rigid Benzo[1,2-b:6,5-b']dithiophene Segment for High-Performance Dye-Sensitized Solar Cells.

Benzo[1,2-b:6,5-b']dithiophene (BDT) entity with rigid skeleton is introduced into the conjugated spacer of organic dyes, with triphenylamine as the electron donor and 2-cyanoacrylic acid as the acceptor, have been prepared for dye-sensitized solar cells. Inserting an aromatic entity between BDT and the anchor extends the absorption wavelength of the dyes and improves the dark current suppression efficiency, and consequently leads to better cell performance. Addition of chenodeoxycholic acid coadsorbent alleviates dye aggregation and results in better cell efficiency. The dye inserted with 4H-cyclopenta[2,1-b:3,4-b']dithiophene entity achieves the best efficiency (9.11%) when I-/I3- was used as the electrolyte. When Co(phen)32+/3+ was used as the electrolyte, the efficiency further boosts to 9.88%.

Synthesis of Spirolactams and Fused Bicyclic Lactams via Acid-Promoted Cyclolactamization of (Ethynyl(tosyl)amino)methyl-Tethered Cyclohex-2-enols.

A simple synthetic method to construct the spirolactam framework from TfOH-catalyzed spirolactamization of cyclohex-2-enols bearing a tethered (arylethynyl(tosyl)amino)methyl moiety is described. The reaction proceeded through a keteniminium-allylic carbocation intermediate. Hydration of the keteniminium ion, followed by attack of the resulting enolate onto the tethered allylic carbocation, provided the spirolactam ring skeleton. This strategy could also be employed in the synthesis of fused bicyclic lactams from BF3·OEt2-assisted cyclolactamization of TBS-protected 2-(ethynyl(tosyl)amino)methylcyclohex-2-enols.

Gold-Catalyzed Stereoselective Synthesis of Bicyclic Lactams and Ketones from N-Tosylynamidomethyl-Tethered Cyclohexenes.

Six-membered ring 3-enynamides underwent cycloisomerization in the presence of a catalytic amount of a gold(I) complex delivering mainly 4-azatricyclo[4.3.1.03,10]dec-2-ene derivatives and dibenz[cd,f]indole derivatives as the minor products under mild reaction conditions. Upon exposure to air, most aryl-substituted azatricycles led to bicyclic γ-lactams, while the ortho-tolyl- or alkyl-substituted azatricycles provided the corresponding bicyclic γ-lactams after oxidation with osmium tetraoxide and N-methylmorpholine-N-oxide. Under acidic conditions, the ortho-tolyl- or alkyl-substituted azatricycles were further transformed into 5-N-tosylaminomethyl-tethered bicyclo[4.2.0]octan-7-ones. The gold(I)-catalyzed tandem cycloisomerization/oxidation reaction also provided a new route for the synthesis of bridged bicyclic δ-lactams from six-membered ring 4-enynamides. The mild reaction conditions allowed the synthesis of a range of bicyclic γ- and δ-lactams and N-tosylaminomethyl-tethered bicyclo[4.2.0]octan-7-ones with high diastereoselectivities.

Iron(II) Halide Promoted Cyclization of Cyclic 2-Enynamides: Stereoselective Synthesis of Halogenated Bicyclic γ-Lactams.

A simple and mild process was developed for the highly stereoselective synthesis of halogenated bicyclic [4.3.0] and [3.3.0] γ-lactams, possessing four stereocenters, from easily available cyclic 2-enynamides. The reaction required only an inexpensive iron(II) halide under dry air and was tolerant of aryl, heteroaryl, and alkyl groups at the alkyne terminus.

Diastereoselective Synthesis of Fluorine-Containing Pyrrolizidines via Triphenylcarbenium Tetrafluoroborate-Promoted Carbofluorination of N-3-Arylpropargylpyrrolidine-Tethered Tertiary Allylic Alcohols.

Inexpensive and air stable triphenylcarbenium tetrafluoroborate efficiently promoted the carbofluorination of N-arylpropargylpyrrolidines bearing a tertiary allylic alcohol tether at the 2-position of the pyrrolidine ring to provide 1-isobutenyl-2-(fluoro(phenyl)methylenylhexahydro-1H-pyrrolizidines in a stereoselective fashion. When subjected to bis(trifluoromethane)sulfonamide, the same substrates underwent cycloisomerization reaction within minutes to generate 1-isobutenyl-2-benzoylhexahydro-1H-pyrrolizidines with excellent stereoselectivity.

Diastereoselective synthesis of 2-arylmethylene-6-hydroxyspiro[4.5]deca-7-ones via FeCl3·6H2O-catalyzed spiroannulation/hydride transfer of 6-(5-arylpent-4-yn-1-yl)-7-oxabicyclo[4.1.0]heptan-2-ols.

In the presence of a catalytic amount of FeCl3·6H2O, 6-(5-arylpent-4-yn-1-yl)-7-oxabicyclo[4.1.0]heptan-2-ols underwent attack of the pendant acetylene at the iron-activated oxirane to give a vinylic carbocation. Hydride transfer from the carbinol carbon to the newly formed cation center furnished 2-arylmethylene-6-hydroxyspiro[4.5]deca-7-ones in excellent stereoselectivity and good yields.

Syntheses of 3,4-disubstituted pyrroles and furans via Lewis acid-promoted semipinacol rearrangement/alkyne-ketone metathesis reaction of (C)-2-N- or O-((3-arylpropargyl)methyl)-tethered 3,5,5-trimethyl-2,3-epoxycyclohexan-1-ones.

The synthesis of 2,3-disubstituted pyrroles via TMSOTf-assisted cyclization reaction of 3,5,5-trimethyl-2,3-epoxycyclohexan-1-ones incorporating a (3-arylpropargyltosylamino)methyl tether at the C-2 position is described. The reaction starts with an acid-promoted semipinacol rearrangement to give a ring contraction cyclopentanone moiety bearing an arylpropargylaminoacetyl side chain. A subsequent alkyne-ketone metathesis affords the pyrrole derivatives in good yields. The 3,4-disubstituted furan analogues can also be available from 3,5,5-trimethyl-2,3-epoxycyclohexan-1-ones with a tethered arylpropargyl methyl ether at the C-2 position and BF3·OEt2 under an atmosphere of oxygen.

Transition-metal-free carbofluorination of TBS-protected nitrogen-containing cyclic enynols: synthesis of fluorinated azabicycles.

The synthesis of fluorinated azabicycles from tert-butyldimethylsilyl-protected N-containing cyclic enynols using inexpensive BF3·OEt2 is described. In this reaction, BF3 reacts as both the Lewis acid and the fluoride source for cyclization/fluorination of the TBS-protected cyclic N-containing enynols. The method provides an easy access to fluorinated azabicycles where a new C(sp(2))-F bond and a new bicyclic skeleton are generated at ambient temperature within 1-13 min under metal-free reaction conditions.

Diastereoselective synthesis of vicinal cis-dihydroxyheterospirocycles by one-pot epoxidation/spirocyclization of C(3)-functionalized cyclohex-2-en-1-ols.

Spirolactones, spirotetrahydrofurans, and spiropyrrolidines containing a vicinal cis-diol adjacent to the spiro-carbon center are prepared by one-pot epoxidation/spirocyclization of cyclohex-2-en-1-ols bearing an ester, alcohol, or amide functional side chain at the C(3) position of the ring.

Synthesis of 2-azaspiro[4.6]undec-7-enes from N-tosyl-N-(3-arylpropargyl)-tethered 3-methylcyclohex-2-en-1-ols.

The FeCl(3)-promoted synthesis of 2-azaspiro[4.6]undec-7-ene rings proceeds via ring expansion/cyclization/chlorination of N-tosyl-N-(3-arylpropargyl)-tethered 6-methylbicyclo[4.1.0]heptan-2-ols. This azaspirocyclic ring skeleton can also be obtained in one pot from the tert-butyldimethylsilyl-protected N-tosyl-N-(3-arylpropargyl)-tethered 3-methylcyclohex-2-en-1-ols and diethylzinc/diiodomethane.

Facile synthesis of azaspirocycles via iron trichloride-promoted cyclization/chlorination of cyclic 8-aryl-5-aza-5-tosyl-2-en-7-yn-1-ols.

A simple and efficient FeCl(3)-promoted cyclization/chlorination of cyclic tosylamine-tethered 8-aryl-2-en-7-yn-1-ols was observed. The reaction proceeded instantaneously at 23 °C in air to afford (Z)-4-(arylchloromethylene)-substituted azaspirocycles in good to excellent yields. This transformation can also be applied to the synthesis of spirocarbocyclic analogues from cyclic 8-aryl-2-en-7-yn-1-ols and FeCl(3).

Arylamine-based dyes for p-type dye-sensitized solar cells.

New arylamine-based sensitizers for p-type dye-sensitized solar cells (DSSCs) have been synthesized and used for p-type DSSCs. The best conversion efficiency reaches ∼0.1%. Sensitizers with two anchoring carboxylic acids lead to higher open-circuit voltages, short-circuit currents, and energy conversion efficiencies.

Synthesis of the phenanthrene and cyclohepta[a]naphthalene skeletons via gold(I)-catalyzed intramolecular cyclization of unactivated cyclic 5-(2-arylethyl)-1,3-dienes.

The gold(I)-catalyzed hydroarylation of cyclohexa-1,3-dienes bearing an aryl group and a gem-diester in the tether proceeds in a 1,4-addition manner and in a diastereoselective fashion to afford perhydrophenanthrene rings. The reaction proceeded via attack of the aryl group onto the gold-activated cyclic dienes followed by rearomatization and protodeauration to generate perhydrophenanthrenes in good yields. This hydroarylation can be applied to the synthesis of perhydrocyclohepta[a]naphthalenes from aryl-tethered cycloheptadienes and the gold(I) catalyst.

Photophysical studies of dipolar organic dyes that feature a 1,3-cyclohexadiene conjugated linkage: the implication of a twisted intramolecular charge-transfer state on the efficiency of dye-sensitized solar cells.

A detailed study of the synthesis and photophysical properties of a new series of dipolar organic photosensitizers that feature a 1,3-cyclohexadiene moiety integrated into the π-conjugated structural backbone has been carried out. Dye-sensitized solar cells (DSSCs) based on these structurally simple dyes have shown appreciable photo-to-electrical energy conversion efficiency, with the highest one up to 4.03 %. Solvent-dependent fluorescence studies along with the observation of dual emission on dye 4 b and single emission on dyes 4 a and 32 suggest that dye 4 b possesses a highly polar emissive excited state located at a lower-energy position than at the normal emissive excited state. A detailed photophysical investigation in conjunction with computational studies confirmed the twisted intramolecular charge-transfer (TICT) state to be the lowest emissive excited state for dye 4 b in polar solvents. The relaxation from higher-charge-injection excited states to the lowest TICT state renders the back-electron transfer process a forbidden one and significantly retards the charge recombination to boost the photocurrent. The electrochemical impedance under illumination and transient photovoltage decay studies showed smaller charge resistance and longer electron lifetime in 4 b-based DSSC compared to the DSSCs with reference dyes 4 a and 32, which further illustrates the positive influence of the TICT state on the performance of DSSCs.

Synthesis of cis-3-acyl-4-alkenylpyrrolidines via gold(I)-catalyzed cycloisomerization reaction of (Z)-8-aryl-5-tosyl-5-azaoct-2-en-7-yn-1-ols.

(Z)-8-Aryl-5-tosyl-5-azaoct-2-en-7-yn-1-ols were cycloisomerized to the corresponding cis-3-acyl-4-alkenylpyrrolidines when treated with a catalytic amount of Ph(3)PAuCl/AgOTf in CH(2)Cl(2). The reaction proceeded via attack of the hydroxyl group onto the gold-activated alkynes followed by [3,3]-sigmatropic rearrangement to generate cis-3-acyl-4-alkenylpyrrolidines in good yields. This transformation can be applied to the synthesis of cis- and trans-3-acyl-4-alkenylcyclopentanes from (Z)- and (E)-8-aryloct-2-en-7-yn-1-ols, respectively.

Organic dyes containing furan moiety for high-performance dye-sensitized solar cells.

New metal-free dyes with a furan moiety in the conjugated spacer between the arylamine donor and the 2-cyanoacrylic acid acceptor have been synthesized, and high efficiency dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers.

Structurally simple dipolar organic dyes featuring 1,3-cyclohexadiene conjugated unit for dye-sensitized solar cells.

A series of structurally simple dipolar light-harvesting organic dyes featuring 1,3-cyclohexadiene in the aromatic pi framework for dye-sensitized solar cells has been synthesized and characterized. The highest conversion efficiency of the DSSCs based on these dyes can reach up to 4.4%.

Synthesis of indenol- and azulenol derivatives via platinum dichloride-catalyzed intramolecular hydroxy- or alkoxycyclization of cyclic dienynes.

Platinum dichloride-catalyzed hydroxy- or alkoxycyclization of cyclohexadienynes gives indenol derivatives, whereas hydroxy- or alkoxycyclization of cycloheptadienynes produces azulenol derivatives. The cyclization reaction proceeds via a cyclopropyl platinacarbene intermediate and allows for the direct stereocontrol of three contiguous stereogenic centers of the fused bicyclic skeletons. The transient reactive intermediate obtained from PtCl2-catalyzed cyclization reaction of a cyclohexadienyndiol can be trapped intramolecularly by a hydroxyl group to afford an oxatricyclo[5.4.0.04,8]undecane ring skeleton with extreme diastereoselectivity.

Nonconjugated red-emitting dendrimers with p-type and/or n-type peripheries.

[reaction: see text] Dendron-encapsulated materials having a benzo[c][1,2,5]thiadiazole-based red-emitting core and p-type and/or n-type peripheries were synthesized. Intra- and intermolecular energy transfer from the peripheries to the core were found to be peripheries dependent. Red-emitting electroluminescent devices with promising performance were fabricated.