BORAZANs: tunable fluorophores based on 2-(pyrazolyl)aniline chelates of diphenylboron

The reaction between 2-pyrazolyl-4-X-anilines, H(pzAnX), (X = para-OMe (L1), Me (L2), H (L3), Cl (L4), CO2Et (L5), CF3 (L6), CN (L7)) and triphenylboron in boiling toluene affords the respective, highly emissive N,N'-boron chelate complexes, BPh2(pzAnX) (X = para-OMe (1), Me (2), H (3), Cl (4), CO2Et (5), CF3 (6), CN (7)) in high yield. The structural, electrochemical, and photophysical properties of the new boron complexes can be fine-tuned by varying the electron-withdrawing or -donating power of the para-aniline substituent (delineated by the substituent's Hammett parameter). Those complexes with electron-withdrawing para-aniline substituents such as CO2Et (5), CF3 (6), and CN (7) have more planar chelate rings, more 'quinoidal' distortion in the aniline rings, greater chemical stability, higher oxidation potentials, and more intense (phiF = 0.81 for 7 in toluene), higher-energy (blue) fluorescent emission compared to those with electron-donating substituents. Thus, for 1 the oxidation potential is 0.53 V versus Ag/AgCl (compared to 1.12 V for 7), and the emission is tuned to the yellow-green but at an expense in terms of lower quantum yields (phiF = 0.07 for 1 in toluene) and increased chemical reactivity. Density functional calculations (B3LYP/6-31G*) on PM3 energy-minimized structures of the ligands and boron complexes reproduced experimentally observed data and trends and provided further insight into the nature of the electronic transitions.     

Bis(phosphine imide)s: easily tunable organic electron donors

[graph: see text] The electrochemical, structural, and spectroscopic properties of bis(phosphine imide)s have been investigated. p-Phenylenebis(phosphine imide)s Ar3PNC6H4NPAr3 (1a-d) have two reversible single-electron oxidations. The first oxidation potentials can be varied from -0.05 to 0.15 V (versus SCE) by modification of the substituents on phosphorus (Ar). Electron-donating substituents lower the oxidation potential, while electron-withdrawing substituents increase the oxidation potential. The difference between the first and second oxidation potential (deltaE, 0.41-0.50) and the electronic coupling (Hab, 1.1 eV) are similar for 1a-d. Computational (DFT) and UV-visible-NIR spectroscopic investigations of 1a-d suggest that the first oxidation leads to a delocalized radical cation 1a*+ while the second oxidation leads to a quinonoidal dicationic state 1a2+. The aromatic linker between phosphine imides has also been modified. Upon oxidation, N,N'-4,4'-biphenylene(bis(triphenyl)phosphine imide) (3) forms radical cationic and a dicationic species similar to 1a-d. While deltaE (0.18 V) and Hab (0.63 eV) are smaller, suggesting weaker electronic communication between the two P=N units in the radical cationic state, the presence of NIR absorptions with vibrational fine structure (768, 861, and 983 nm) supports the formation of delocalized radical cation for 3*+.     

Synthesis and photophysical studies of bis-enediynes as tunable fluorophores

We have synthesized a family of bis-enediynes by two complementary Pd/Cu-catalyzed Sonogashira cross-coupling methods. One is a modified Sonogashira reaction between the TMS-protected tetraalkyne 20 (or 21) and various aromatic bromides to afford bis-enediynes 22a-d and 23a-d bearing different peripheral aryl units. The other, the reaction of bifunctional 1,1-dibromo-1-alkenes with phenylacetylene, afforded a series of bis-enediynes 24-32 bearing various core aryl groups. These chemical modifications to the core and periphery of bis-enediynes induce dramatic changes in absorption and emission spectra. Bis-enediynes 22 and 23 show a large Stokes shift of about 50-110 nm when compared to the less-conjugated bis-enediynes 20 and 21. Absorptions and emissions of bis-enediynes 25, 27-29, and 31 were red-shifted relative to those of enediyne 35. Substantial increases in fluorescence quantum yields are observed as a result of extending the pi-conjugation. The emission wavelength of bis-enediynes was tailored from indigo blue to reddish-orange, suggesting that the color of emission can be tunable by modification of the core and/or peripheral units.     

First Synthesis of Bis(di(indolyl)aryl)methanes From Bis(salicylaldehydes)

In this article, a simple method for the synthesis of bis(di(indolyl)aryl)methanes is described. The iodine‐catalyzed (5 mol %) reaction of indoles with various bis(salicylaldehyde) derivatives affords the bis(di(indolyl)aryl)methanes in excellent yields. The reaction works well under mild reaction condition with shorter reaction time.     

Synthesis of Bis(phosphonatomethyl)-, Bis(phosphinatomethyl)-, and Bis(phosphinoxidomethyl)amines,as Well as Related Ring Bis(phosphine) Platinum Complexes

The double Kabachnik–Fields condensation of primary amines with 2 equivalents of the other reagents (formaldehyde and a >P(O)H species, such as dialkyl phosphites, diphenylphosphine oxide, as well as the related dioxaphosphorine and oxaphosphorine derivatives) carried out under microwave conditions afforded the title products in 79–94% yields. The bis(phosphinoxidomethyl)amines were converted, after double deoxygenation, to the corresponding ring platinum complexes.

Bis(fluorobenzoyloxy)methylphosphansulfide

Bis(fluorobenzoyloxy)methyl phosphane sulfides CH₃P(S) [OC(O)R]₂ [R = C₆H₄-2-F (1), C₆H₄-3-F (2), C₆H₄-4-F (3), C₆H₃-2,6-F₂ (4), and C₆F₅ (5)] were prepared by treating silver salts of carboxylic acids AgOC(O)R with CH₃P(S)Cl₂ and characterised by IR- and NMR-spectroscopy. Compared to bis(fluorobenzoyloxy)methylphosphane oxides, there is less tendency towards formation of symmetrical anhydrides and greater stability to hydrolysis.