Thiazolidine derivatives from fluorescent dithienyl-BODIPY-carboxaldehydes and cysteine.

Fluorescent dithienyl-borondipyrromethene (BODIPY) dyes formylated in the ß'-position (2b, 2c) have been treated with L-cysteine to provide thiazolidine derivatives. N-Protection of the thiazolidine unit by ethoxycarbonylation facilitated isolation of the two major diasteroisomers 6 and 7. These stereoisomers have been fully characterized by (1)H NMR spectroscopy, allowing assignment of their stereochemistry as 2R,4R,aS and 2S,4R,aR, respectively. The optical properties of the thiazolidine dyes differ markedly in both absorption (λ(abs) = 612 nm for 6 and 615 nm for 7) and emission (λ(em) = 669 nm, Φ(F) = 62% for 6 and λ(em) = 672 nm, Φ(F) = 19% for 7) from those of the BODIPY-carboxaldehydes 2b (λ(abs) = 643 nm and λ(em) = 719 nm, Φ(F) = 26%) and 2c (λ(abs) = 636 nm and λ(em) = 710 nm, Φ(F) = 36%). In a mixed solvent [phosphate buffer saline (PBS), pH = 7.4/ethanol 1:9], the fluorescence response of the dyes in the presence of L-cysteine is slow, but a ratiometric detection process in the therapeutic window (650 to 800 nm) is evident.

Synthesis of water-soluble red-emitting thienyl-BODIPYs and bovine serum albumin labeling.

The synthesis of three red-emitting and water-soluble thienyl-BODIPYs has been achieved. The trimethyl(propargyl)ammonium group was chosen as a vector for water solubility. One or two cationic arms were introduced either on the 2-position of the thienyl unit or on the 4-position on the boron atom. These dyes have pronounced absorption around 600 nm and intense emission at 650 nm with quantum yield of about 60% in water. Grafting of such BODIPYs via a flexible arm to BSA is very efficient, allowing attachment of 1 to 30 labels in a controlled manner. Very strong fluorescence (quantum yield 56%)without aggregation of the dye at a low loading ratio (1:5 BSA/label) in PBS buffer is measured.

Fluorescent boron(III) iminocoumarins (Boricos).

Complexation of iminocoumarin derivatives with BF3·OEt2 provides novel N^N boron(III) dyes exhibiting high absorption coefficients and quantum yields as great as 81%. The excellent chemical stability of these dyes enables the grafting of Boranil or Bodipy units to give derivatives in which the Borico subunit can act either as an energy acceptor or as an antenna for a red emitting fluorophore.

Oligothienyl-BODIPYs: red and near-infrared emitters.

The synthesis of unsymmetrical 3,5-dioligothienyl-BODIPY derivatives and their optical and redox properties are reported. The key step is the monobromination of the 2,6-dimethyl-3,5-dithienyl-BODIPY at the α position of the thiophene moiety. The additional thiophene modules are attached by palladium-catalyzed cross-coupling reactions. Increasing the number of modules on each side of the BODIPY core progressively shifts the absorption to 677 nm and the emission to 769 nm.

Synthetic routes to fluorescent dyes exhibiting large Stokes shifts.

Derivatives of isomeric 2-(hydroxytolyl)-4,6-dimethylamino-1,3,5-triazines have been synthesized in high yields in a controlled manner using a multistep reaction sequence. Iodination of either 2-(1'-hydroxy-6'-methylphen-2'-yl)- or 2-(1'-hydroxy-4'-methylphen-2'-yl)-4,6-dimethylamino-1,3,5-triazine with ICl provides species differing in the positioning of the iodo group relative to the hydroxyl which readily undergo Suzuki, Sonogashira, and Heck reactions under Pd(0) catalysis. Thus, thienyl, bisthienyl, and 3,4-ethylenedioxythienyl groups have been directly grafted, while unsubstituted polycyclic aromatics such as pyrene and perylene have been linked via alkyne bridges, as have ethynyldifluoroborondipyrromethane (BODIPY) dyes prepared in situ. The presence of a hydrogen bond in the ground state involving the hydroxyl substituent has been established by proton NMR and several X-ray structure determinations. All of the new dyes with a simple substituent (phenyl, thienyl) exhibited a pronounced green fluorescence resulting from an intramolecular proton transfer in the excited state (ESIPT) which produces a large Stokes shift (>10,000 cm(-1)). With other dyes, the fluorescence of the keto form responsible for the ESIPT process could be used as the input energy in efficient intramolecular energy transfer processes. Replacing perylene with pyrene allowed reversal of the direction of energy transfer from the polyaromatic module to the keto form.

Oxidative coupling of 1,7,8-unsubstituted BODIPYs: synthesis and electrochemical and spectroscopic properties.

We report the synthesis of BODIPYs with unsubstituted 1,7,8-positions and their dimerization by oxidative coupling with phenyliodine(III)-bis(trifluoroacetate) (PIFA). This dimerization was achieved for BODIPYs substituted in the 3,5-positions with either methyl or thienyl groups. The position and the type of the linkage in the resulting dimers depended on the nature of the substituent. The 3,5-dimethyl-BODIPY dyes were linked either via direct 1,1'-pyrrole-pyrrole coupling or via a 1,3'-methylene bridge. The 3,5-dithienyl-BODIPY dyes provided, in excellent yields, unique compounds linked exclusively via the α-thienyl positions. All dyes were unreactive in the 8-position. Electrochemical and spectroscopic measurements on the monomers and dimers provided evidence of interactions between the two halves of the dimers. Thus, oxidation and reduction potentials were split by up to 210 mV, and modest excitonic coupling and an internal charge transfer were observed in some cases.

Chemistry at boron: synthesis and properties of red to near-IR fluorescent dyes based on boron-substituted diisoindolomethene frameworks.

A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure-fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650-800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13,000 cm(-1) depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications.

Phenyliodine(III) bis(trifluoroacetate) (PIFA)-promoted synthesis of Bodipy dimers displaying unusual redox properties.

Phenyliodine(III) bis(trifluoroacetate) (PIFA) in conjunction with a Lewis acid promotes C-C coupling of Bodipy monomers leading to mixtures of various oligomers. When a single position is blocked with an iodo or phenyl group, formation of the dimer is favored. These dimers display two successive oxidation and two reduction waves separated on average by 260 and 130 mV, respectively, corresponding to each Bodipy subunit.

A tailored hybrid BODIPY-oligothiophene donor for molecular bulk heterojunction solar cells with improved performances.

Fixation of a 5-hexyl-2,2'-bithienyl unit on a conjugated BODIPY donor increases the conversion efficiency of the resulting molecular bulk heterojunction solar cells from 1.30 to 2.20%.

Spectroscopic and redox properties of novel d6-complexes engineered from all Z-ethenylthiophene-bipyridine ligands.

A series of quasilinear dinuclear complexes incorporating ruthenium(II)- and osmium(II)-tris(2,2'-bipyridine) units has been prepared in which the individual metal-containing moieties are separated by 3,4-dibutyl-2,5-diethenylthiophene spacers and end-capped by 3,4-dibutyl-2-ethenylthiophene subunits; related ruthenium(II) and osmium(II) mononuclear complexes have also been prepared where one bpy unit is likewise end-capped by 3,4-dibutyl-2-ethenylthiophene subunits [bpy = 2,2'-bipyridine]. Overall, mononuclear species, labeled here Ru and Os, and dinuclear species, RuRu, OsOs, and RuOs, have been prepared and investigated. Their electrochemical behavior has been studied in CH3CN solvent and reveals ethenylthiophene-centered oxidations (irreversible steps at > +1.37 V vs SCE), metal-centered oxidations (reversible steps at +1.30 V vs SCE for Ru(II/III) and +0.82 V vs SCE for Os(II/III)), and successive reduction steps localized at the substituted bpy subunits. The spectroscopic studies performed for the complexes in CH3CN solvent provided optical absorption spectra associated with transitions of ligand-centered nature (LC, from the bpy and ethenylthiophene subunits) and metal-to-ligand charge-transfer nature (MLCT), with the former dominating in the visible region (400-600 nm). While the constituent ethenylthiophene-bpy ligands are strong fluorophores (fluorescence efficiency in CH2Cl2 solvent, phi em = 0.49 and 0.39, for the monomer and the dimer, respectively), only weak luminescence is observed for each complex in acetonitrile at room temperature. In particular, (i) the complexes Ru and RuRu do not emit appreciably, and (ii) the complexes Os, OsOs, and RuOs exhibit triplet emission of 3Os --> L CT character, with phi em in the range from 10-3 to 10-4. These features are rationalized on the basis of the role of nonemissive triplet energy levels, 3Th, centered on the ethenylthiophene spacer. These levels appear to lie lower in energy than the 3Ru --> L CT triplet levels, and in turn higher in energy than the 3Os --> L CT triplet levels, along the sequence 3Ru --> L CT > 3Th > 3Os --> L CT.

Photophysical properties of ruthenium(II) tris(2,2'-bipyridine) complexes bearing conjugated thiophene appendages.

A small series of ruthenium(II) tris(2,2'-bipyridine) complexes has been synthesized in which ethynylated thiophene residues are attached to one of the 2,2'-bipyridine ligands. The photophysical properties depend on the conjugation length of the thiophene-based ligand, and in each case, dual emission is observed. The two emitting states reside in thermal equilibrium at ambient temperature and can be resolved by emission spectral curve-fitting routines. This allows the properties of the two states to be evaluated in both fluid butyronitrile solution and a transparent KBr disk. It is concluded that both emitting states are of metal-to-ligand charge-transfer (MLCT) character, and despite the presence of conjugated thiophene residues, there is no indication for a low-lying pi,pi*-triplet state that promotes nonradiative decay of the excited-state manifold. A key feature of these systems is that the conjugation length imposed by the thiophene-based ligand helps to control the rate constants for both radiative and nonradiative decay from the two MLCT triplet states.

Energy transfer in hybrids based on a thiophene-substituted ethynylbipyridine dimer decorated with Re(I), Ru(II), and Os(II) units.

The preparation, structural features, electrochemical behavior, and optical properties (at room temperature and at 77 K) are reported for a series of thiophene-containing hybrids based on the bent conjugated backbone of a rigid ditopic ligand, the dimeric moiety 3,4-dibutyl-2,5-bis{5'-[(3,4-dibutylthien-2-ylethynyl)-2,2'-bipyridin-5-yl]ethynyl}thiophene (TBTBT). Within the dimer, the diethynyl-2,2'-bipyridine units (bpy, the coordination sites) alternate with three 3,4-dibuthylthiophene units and coordination of the [Re(CO)3Cl], [Ru(bpy)2]2+, and [Os(bpy)2]2+ centers results in the mononuclear species RuTBTBT and OsTBTBT and the binuclear species RuTBTBTRu, OsTBTBTOs, RuTBTBTOs, and ReTBTBTOs. At room temperature, the emitting states obtained by photoexcitation are of 3MLCT nature, and vibronic analysis of the emission spectra indicates that they are largely delocalized over the TBTBT ligand. In the binuclear species, the intermetal separation is ca. 17 A, and for RuTBTBTOs, an efficient Ru --> Os excitation transfer takes place, resulting solely in an Os-based emission. The process is ascribed to double-electron transfer (Dexter), as mediated by the TBTBT ligand; a similar conclusion holds for the case of ReTBTBTOs. For RuTBTBTOs, the process is discussed in some detail also with regard to the possibility of disentangling the constituent hole and electron-transfer events.

Controlled synthesis of multinuclear metal complex arrays by cross coupling of coordinated ligands.

Conditions for efficient cross linking of chelating organic ligands within different metal-containing building blocks have been developed, allowing the preparation of heteronuclear Ru/Os complexes in a controlled manner. Critical to the success of this protocol is the introduction of an Os center early in the synthesis and the use of CuI under polar conditions. Noteworthy features of this method are the tolerance of the metal centers in both reaction partners and the absence of any metal scrambling during the C-C formation or ultimate complexation procedures.

Oligomeric ligands incorporating multiple 5,5'-diethynyl-2,2'-bipyridine moieties bridged and end-capped by 3,4-dibutylthiophene units.

In this work, we detail the synthesis and photophysical properties of a series of soluble polybipyridine ligands comprising one to five bipyridine units sandwiched between rigid carbon-carbon triple bonds substituted by 3,4-dibutylthiophene repeating units. The dual Sonogashira coupling reaction of 5,5'-dibromo-2,2'-bipyridine with TMS- and (CH3)2C(OH)-protected acetylene allows the synthesis of a dissymmetrically functionalized building block which was selectively deprotected at either the TMS or 2-hydroxyprop-2-yl site. Various combinations allow the interconnection of the terminal alkyne to 3,4-dibutyl-2,5-diiodothiophene or 3,4-dibutyl-2-iodothiophene leading to bipyridine frameworks bearing two acetylene-protected groups or one acetylenethiophene/one acetylene-protected function. It is possible therefore to construct dimeric to pentameric bipyridine ligands where the chelating subunit is bridged by a 3,4-dibutyl-2,5-diethynylthiophene spacer and end-capped by a 3,4-dibutyl-2-ethynylthiophene stopper. All cross-coupling reactions are promoted with palladium(0) tetrakistriphenylphosphine under mild conditions. Spectroscopic data for the new oligomers are discussed in terms of the extent of pi-electron conjugation. Upon increasing the number of pi-electrons from 24 to 104, there is a progressive lowering in the energy of absorption and fluorescence transitions, while the emission quantum yields remain essentially constant. The LUMO levels of these large molecules, estimated by cyclic voltammetry, lie in the range -3.06 to -3.18 eV.

Mononuclear and binuclear wirelike ruthenium(II) complexes with oligo-diethynyl-thiophene bridged back-to-back terpyridine ligands: synthesis and electrochemical and photophysical properties.

The syntheses, structural features, electrochemical behavior, absorption spectra, and photophysical properties of five mononuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)](2+), RuT(n), and five binuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)Ru(terpy)](4+), RuT(n)Ru, are reported, where n varies from 1 to 5 so that the metal-metal distance is estimated to be 42 A for the largest binuclear complex, RuT(5)Ru (terpy is 2,2':6',2"-terpyridine and DEDBT is 2,5-diethynyl-3,4-dibutylthiophene). The metal-centered oxidation potentials for the mononuclear and binuclear species are slightly more positive than for the reference [Ru(terpy)(2)](2+) complex, owing to the withdrawing nature of the back-to-back terpyridine ligands incorporating the repeat diethynyl-thiophene units. Comparison of the reduction potentials for the mononuclear and binuclear complexes reveals that the reduction steps are localized either at the terpy fragments of the T(n) ligands or at the terpy peripheral ligands. The spectroscopic results (absorption spectra at room temperature, luminescence spectra and lifetimes at room temperature and at 77 K) in acetonitrile solvent are consistent with the establishment of electronic delocalization within the oligomeric diethynyl-thiophene fragments (DEDBT(n)) of the T(n) ligands; however, the results also indicate that the terpy units of these ligands and the DEDBT(n)fragments are not strongly coupled. Both at room temperature and at 77 K, the (3)metal-to-ligand charge-transfer luminescence of RuT(n) and RuT(n)Ru complexes is strongly depressed in the larger species with respect to what happens for n < or = 2 (where the luminescence quantum yield is phi approximately 10(-4)); this is discussed in terms of the possible intervention of triplet levels localized at the oligothiophene DEDBT(n)(fragments.

A concise modular synthesis of 2,5-diethynyl-3,4-dibutyl-thiophene-bridged back-to-back terpyridine ligands.

The efficient synthesis of soluble and rigid terpyridine-based ditopic ligands bearing an increasing number of 2,5-diethynyl-3,4-dibutylthiophene (DEDBT) modules has demonstrated the advantages of a single convergent strategy based on a double coupling in a final step of monoterpyridine building blocks carrying the adequate number of thiophene modules with a diiodo-substituted thiophene subunit. This protocol enjoys the advantages of both efficiency and versatility and requires pivotal intermediates, which were produced by a step-by-step implementation of monoterpyridine fragments with a key thiophene intermediate carrying an iodo function, a propargylic-protecting group, and two butyl-solubilizing fragments. One set of experimental conditions is required to produce all the intermediates and the final ligands. Oxidative dimerization of monosubstituted terpyridine skeletons bearing one or two thiophene substituents and a terminal alkyne function, in the presence of cupric salts and oxygen, afforded the homotopic ligands with a central dithienylbutadiyne spacer. Optical properties for the new oligomers have been investigated and are discussed in terms of effective conjugation length and pi-electron conjugation. Upon increasing the number of interspersed DEDBT units, a significant lowering in energy of absorption and fluorescence transitions as well as of the quantum yields is observed.

One-pot synthesis of 2,5-diethynyl-3,4-dibutylthiophene substituted multitopic bipyridine ligands: redox and photophysical properties of their ruthenium(II) complexes.

A facile and original synthesis of four 2,2'-bipyridine (bipy) ligands grafted with thiophene subunits is described using phase transfer experimental conditions: related Ru(II) complexes exhibit well-defined redox and photophysical properties which were probed by cyclic voltammetry, UV-vis, steady-state emission and transient absorption spectroscopy.