Fluorescence spectroscopic properties and crystal structure of a series of donor-acceptor diphenylpolyenes

A series of p-nitro-p'-alkoxy(OR)-substituted (E,E,E)-1,6-diphenyl-1,3,5-hexatrienes (1a, R = Me; 1b, R = Et; 1c, R = n-Pr; 1d, R = n-Bu) were prepared. The absorption and fluorescence spectra in solution were almost independent of the alkoxy chain length. The absorption maximum showed only a small dependence on the solvent polarity, whereas the fluorescence maximum red-shifted largely as the polarity increased. The solid-state absorption and fluorescence spectra were red-shifted relative to those in low polar solvents and were clearly dependent on the alkoxy chain length. The fluorescence maxima for the crystals of 1b and 1d were observed at 635-650 nm, which were red-shifted by 40-50 nm relative to those for 1a and 1c. The Stokes shifts were all relatively small (3000-3500 cm-1). For all four compounds, the fluorescence decay curves in the solid state were able to be analyzed by single-exponential fitting to give the lifetimes of 1.1-1.3 ns. This indicates that the emission of 1a-d is not originated from an excimer or molecular aggregates, but from only one emitting monomeric species. The fluorescence quantum yields of 1a-d were considerably high compared with the values for organic solids, which is consistent with their monomeric origin of emission. Single-crystal X-ray structure analyses of 1a, 1c, and 1d showed that the crystal packing was dependent on the alkoxy chain length. The crystals of 1a and 1c had herringbone structure, whereas that of 1d had pi-stacked structure. Strong pi-pi interaction in the crystal of 1d would be the cause of the spectral red shifts relative to those for 1a and 1c. No observation of excimer fluorescence from crystal 1d can be attributed to the limited overlap between the pi-planes of the molecules due to its "slipped-parallel" structure.     

Superstructure-dependent optical and electrical properties of an unusual face-to-face, pi-stacked, one-dimensional assembly of dehydrobenzo[12]annulene in the crystalline state

To develop a novel pi-conjugated molecule-based supramolecular assembly, we designed and synthesized trisdehydrotribenzo[12]annulene ([12]DBA) derivative 2 with three carboxyl groups at the periphery. Recrystallization of 2 from DMSO gave a crystal of the solvate 23 DMSO. Crystallographic analysis revealed, to our surprise, that a face-to-face pi-stacked one-dimensional (1D) assembly of 2 was achieved and that the DMSO molecule played a significant role as a "structure-dominant element" in the crystal. This is the first example of [12]DBA to stack completely orthogonal to the columnar axis. To reveal its superstructure-dependent optical and electrical properties, 2 and its parent molecule 1, which crystallizes in a herringbone fashion, were subjected to fluorescence spectroscopic analysis and charge-carrier mobility measurements in crystalline states. The 1D stacked structure of 2 provides a red-shifted, broadened, weakened fluorescence profile (lambda(max) = 545 nm, phi(F) = 0.01), compared to 1 (lambda(max) = 491 nm, phi(F) = 0.12), due to strong interactions between the p orbitals of the stacked molecules. The charge-carrier mobility of the single crystal of 23 DMSO, as well as 1, was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The single crystal of 23 DMSO revealed significantly-anisotropic charge mobility (sigma(mu) = 1.5x10(-1) cm(2) V(-1) s(-1)) along the columnar axis (crystallographic c axis). This value is 12 times larger than that along the orthogonal axis (the a axis).     

1,10-Phenanthrolines with tunable luminescence upon protonation: a spectroscopic and computational study

We have synthesized nine 2,9-aryl-substituted 1,10-phenanthrolines (1-9) with the aim of rationalizing their electronic absorption and luminescence properties in both the basic and acid form. The latter are generated upon addition of trifluoroacetic acid to CH2Cl2 solutions of 1-9 and their formation is unambiguously evidenced by UV-vis absorption and 1H NMR spectroscopy. 1-9 can be subdivided into three groups, depending on their chemical structure and luminescence behavior. 1-3 are symmetrically substituted p-dianisylphenanthrolines which exhibit relatively intense violet fluorescence in CH2Cl2 (lambda(max) ca. 400 nm, Phi(fl) = 0.12-0.33) and are strongly quenched and substantially red-shifted upon protonation (lambda(max) ca. 550 nm, Phi(fl) = 0.010-0.045). 4-5 are 2,6-dimethoxyphenylphenanthrolines with faint luminescence in both the basic and acid form. 6-9 are various unsymmetric aryl-substituted-phenanthrolines and their relatively strong fluorescence (lambda(max) ca. 400 nm, Phi(fl) = 0.08-0.24) is red-shifted and substantially enhanced following protonation (lambda(max) ca. 475 nm, Phi(fl) = 0.16-0.50). The markedly different trends in the electronic absorption and fluorescence spectra are rationalized by means of both time-dependent Hartree-Fock and density functional theory by using hybrid functionals to assign the excited states. Interestingly, protonation of 1-9 also occurs in spin-coated films simply exposed to vapors of acid, and the reaction can be signaled by the color tuning of the emission signal (vapoluminescence). This observation makes substituted phenanthrolines potential candidates as proton sensors also in the solid phase.     

Synthesis of highly soluble and oxidatively stable tetraceno[2,3-b]thiophenes and pentacenes

A comparative study of suitably functionalized, highly soluble tetraceno[2,3-b]thiophenes (1-3) and pentacenes (4-6) that show higher photoxidative stability than that of unfunctionalized corresponding acenes is reported. The absorption and emission of 1-3 (Amax = 624-656 nm, lambda max = 634-672 nm, PhiF approximately 10%) and 4-6 (Amax = 672-704 nm, lambda max = 682-718 nm, PhiF approximately 10%) were found to be systematically red-shifted by the substitution in the order of the tert-butylethynyl < triisopropylsilylethynyl < phenylethynyl groups. The oxidation potentials of these compounds were similar (E1/2 approximately 0.70 V), except for 4, which showed lower oxidation potential (E1/2 approximately 0.63 V).     

An exceptional red shift of emission maxima upon fluorine substitution

The effect of perfluorination on photophysical properties was investigated through synthesis and photophysical characterization of two isostructural donor-acceptor-donor dye molecules. The synthesis of two versatile fluorinated benzene compounds, 1,4-difluoro-2,5-diperfluorooctylbenzene (1) and 1,4-dibromo-2,5-difluoro-3,6-diperfluorooctylbenzene (2), is presented. The X-ray structure of 2 has been determined and shows that the perfluorinated octyl chains segregate from the benzene rings in the solid state, giving rise to a layered structure. The further synthesis through Suzuki coupling reactions using 4-formylbenzeneboronic acid with (2) and 1,4-dibromo-2,5-dioctylbenzene (3) gave, respectively, 1,4' '-diformyl-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (4) and 1,4' '-diformyl-2',5'-dioctyl-p-terphenylene (5). The condensation of the dialdehydes 4 and 5 with 9,10-phenanthrenequinone and ammoniumbicarbonate in glacial acetic acid gave the dye molecules 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (6) and 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-dioctyl-p-terphenylene (7), respectively. The UV-vis spectra of the two molecules are nearly identical, whereas the fluorescence spectra are very different. Compound 7 shows blue fluorescence with little solvent dependence (lambda(emission) = 410 nm in THF, CH2Cl2, and hexane), whereas compound 6 shows a highly solvent-dependent emission wavelength (lambda(emission) = 583 nm in THF, lambda(emission) = 560 nm in CH2Cl2, and lambda(emission) = 450 nm in hexane). The fluorescence red shift of compound 6 in a series of solvents with different polarity is discussed using the Lippert-Mataga equation. Fluorescence lifetime and quantum yields were also determined. Ultraviolet photoelectron spectroscopy (UPS) was performed on thin films of compound 6 and 7 on a gold substrate. The observed ionization potential was 6.15 eV for 6 and 5.85 eV for 7" [correction].     

Synthesis and self-association, absorption, and fluorescence properties of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes

The dual Sonogashira coupling reactions of 1,3,5-tribromo-2,4,6-triiodobenzene with p-X-phenylacetylene followed by another p-Y-phenylacetylene (X, Y = OSiMe(2)Bu-t or CO(2)Et) produced a series of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes with D(3)(h)() symmetry (3h: 1,3,5-X-2,4,6-Y) and C(2)(v)() symmetry (3g,i: 1,2,3,5-X-4,6-Y; 3f,j: 1-X-2,3,4,5,6-Y). In a similar manner, 1,3,5-tris(p-X-phenylethynyl)-2,4,6-tris(p-Y-phenylethynyl)benzenes and 1,2,3,5-tetrakis(p-X-phenylethynyl)-4,6-bis(p-Y-phenylethynyl)benzenes (3l: X = OSiMe(2)Bu-t, Y = NO(2); 3m,n: X = N(n-octyl)(2), Y = NO(2); 3o,p: X = N(n-octyl)(2), Y = CH(OCH(2)CH(2)O); 3q,r: X = N(n-octyl)(2), Y = CHO; 3s,t: X = N(n-octyl)(2), Y = CH=C(CN)(2)) were prepared. Compounds 3 with electron-withdrawing groups self-aggregated by a pi-pi stacking interaction and solvophobic effect. In the absorption and fluorescence spectra of 3, lambda(max)(abs) and lambda(max)(em) showed red shifts as the donor-acceptor dipole at the end functional groups of the para position was increased. In the absorption spectra, lambda(max)(abs) showed red shifts upon increasing the number of combination of electron-donating and -withdrawing groups on the diagonal line in a molecule, whereas lambda(max)(em) in the fluorescence spectra exhibited red shifts upon decreasing the molecular symmetry.     

Cyclometalated platinum(II) complexes of pyrazole-based, N=C=N-coordinating, terdentate ligands: the contrasting influence of pyrazolyl and pyridyl rings on luminescence

1,3-Bis(1-pyrazolyl)-5-methyl-benzene, HL(2), undergoes cyclometalation at the C(2) position upon reaction with K(2)PtCl(4), to generate an N=C=N-coordinated complex, PtL(2)Cl. This compound is luminescent in degassed solution at 298 K, emitting in the blue region of the spectrum on the microsecond time scale (lambda(max) = 453 nm, tau = 4.0 micros, Phi(lum) = 0.02, in CH(2)Cl(2)). Compared to the analogous complex Pt(dpyb)Cl that incorporates pyridyl rather than pyrazole rings {dpybH = 1,3-di(2-pyridyl)-benzene}, the excited state is displaced to higher energy by 1700 cm(-1). This effect is rationalized in terms of the poorer pi-acceptor nature of pyrazolyl compared to pyridyl rings, leading to destabilization of the lowest unoccupied molecular orbital, which is largely localized on the heteroaromatic rings in both cases. Cyclic voltammetry and density functional theory calculations reinforce this interpretation, and suggest that the lowest-energy excited state is probably best described as heavily mixed pi(L)/d(Pt)/p(Cl) --> pi*(L) (IL/MLCT/LLCT) in character. 5-Aryl-substituted analogues of HL(2) are accessible in three steps from 1,3,5-tribromobenzene by Pd-catalyzed cross-coupling with aryl boronic acids, followed by copper-catalyzed bromo-iodo exchange, and subsequent amination with pyrazole under relatively mild conditions also catalyzed by copper. The corresponding Pt(II) complexes display red-shifted and more intense luminescence compared to PtL(2)Cl. Ligands incorporating one pyrazole and one pyridyl ring are also accessible; for example, 1-(1-pyrazolyl)-3-(2-pyridyl)benzene, HL(6). Their complexes are highly luminescent in solution; for example, for PtL(6)Cl, lambda(max) = 487 nm, tau = 6.9 micros, Phi(lum) = 0.55, in dilute solution in CH(2)Cl(2). At elevated concentrations, PtL(6)Cl displays an additional excimeric emission band that is substantially blue-shifted compared to that displayed by Pt(dpyb)Cl (bands centered at 645 and 695 nm, respectively), indicating that the presence of the pyrazole ring destabilizes the excimer. The introduction of a methyl substituent into the central aryl ring of such complexes is sufficient to eliminate the excimer emission.     

Ratiometric fluorescence detection of pyrimidine/purine transversion by using a 2-amino-1,8-naphthyridine derivative.

A new class of abasic site-binding fluorescence ligands, Naph-NBD in which 7-nitrobenzo-2-oxa-1,3-diazole (NBD) is connected to 2-amino-7-methyl-1,8-naphthyridine (Naph) by a propylene linker, is presented for the ratiometric assay for SNPs typing. In solutions buffered to pH 7.0 (I = 0.11 M, at 5 degrees C), Naph-NBD is found to selectively recognize pyrimidine bases over purine bases opposite the abasic site in DNA duplexes (K11/M(-1): T, 8.1 x 10(6); C, 2.5 x 10(6): G, 0.33 x 10(6); A, 0.27 x 10(6)). The binding of Naph-NBD is accompanied by significant quenching of the fluorescence from the naphthyridine moiety (lambda max, 409 nm), while the emission from the NBD (lamda max, 544 nm) is relatively unaffected. Such a fluorescence response of Naph-NBD allows the emission ratio detection of pyrimidine/purine transversion.     

Luminescent Zn and Pd tetranaphthaloporphyrins

Zn and Pd complexes of meso-tetraphenyltetranaphthaloporphyrins (Ph(4)TNP) exhibit strong infrared absorption bands and luminesce in solutions at room temperature. S1 --> S0 fluorescence (lambda(max) = 732 nm, phi = 5.3%) is the predominant emission in the case of ZnPh(4)TNP (1). This emission is in part due to the delayed fluorescence (phi = 1.1%). Phosphorescence (T1 --> S0) of 1 (lambda(max) = 973 nm) is very weak (phi = 0.04%) and occurs with lifetime of about 440 micros in deoxygenated DMF. In the case of PdPh(4)TNP (2), almost no S1 --> S0 fluorescence could be observed, while the main emission detected was T1 --> S0 phosphorescence (lambda(max) = 938 nm). The phosphorescence of 2 occurs with lifetime of about 65 micros and (phi=6.5%) in deoxygenated DMF solution. Metalloporphyrins 1 and 2 are promising near infrared dyes biomedical applications.     

Cation coordination induced modulation of the anion sensing properties of a ferrocene-imidazophenanthroline dyad: multichannel recognition from phosphate-related to chloride anions

A new chemosensor molecule 1 based on a ferrocene-imidazophenanthroline dyad, effectively recognizes aqueous hydrogenpyrophosphate and the organic anions ADP and ATP through three different channels. A cathodic shift of the ferrocene/ferrocenium oxidation wave (Delta E 1/2 ranging from -130 mV for hydrogenpyrophosphate and fluoride to -40 mV for ADP). A progressive red-shift of the absorption bands and/or appearance of a new low energy band at 314-319 nm. These changes in the absorption spectra are accompanied by color changes from pale yellow to orange or pink, which allow the potential for "naked eye" detection. The emission spectrum (lambda exc = 390 nm) undergoes an important chelation-enhanced fluorescence effect (CHEF = 50) in the presence of 2.5 equiv of hydrogenpyrophosphate anion and with a large excess of fluoride anion (CHEF = 114). Interestingly, the emission spectrum obtained at different excitation energy (lambda exc = 340 nm) in the presence of AcOH acid is red-shifted and not only perturbed by the hydrogenpyrophosphate anion (CHEF = 71) but also with the organic anions ATP (CHEF = 25), ADP (CHEF = 15), and the dihydrogenphosphate (CHEF = 25). The stable heterobimetallic ruthenium (II) complex 2 selectively senses the chloride anion over other anions examined through two channels: cathodic redox shift (Delta E 1/2 = -80 mV) of the Fe(II)/Fe(III) redox couple keeping the oxidation wave of the ruthenium (II) center unchanged and a significant red emission enhancement (CHEF = 30). (1)H and (31)P NMR studies as well as DFT calculations have been carried out to get information about which molecular sites are involved in bonding. About the deprotonation/coordination dualism, the combined electrochemical, absorption, emission, and NMR data strongly support that fluoride anion induces only deprotonation, anions dihydrogenphosphate, ATP, and ADP from hydrogen-bonded complexes and formation of hydrogen-bonded complex between receptor 1 and hydrogenpyrophosphate anion and deprotonation proceed simultaneously. In regards to receptor 2, all available data (electrochemical, absorption, emission, and 1H NMR) strongly support the formation of a [2. Cl ( - ) ] hydrogen-bonded complex.     

Exciplex and excimer molecular probes: detection of conformational flip in a myo-inositol chair

2-O-tert-Butyldimethylsilyl-4,6-bis-O-pyrenoyl-myo-inositol-1,3,5-orthoformate (6) and 2-O-tert-butyldimethylsilyl-4-O-[4-(dimethylamino)benzoyl]-6-O-pyrenoyl-myo-inositol-1,3,5-orthoacetate (10) adopt conformationally restricted unstable chairs with five axial substituents. In the symmetrical diester 6, the two pi-stacked pyrenoyl groups are electron acceptor-donor partners, giving a strong intramolecular excimer emission. In the mixed ester 10, the pyrenoyl group is the electron acceptor and the 4-(dimethylamino)benzoyl ester is the electron donor, giving a strong intramolecular exciplex emission. The conformation of the mixed ester 10 was assessed using 1H NMR spectroscopy (1H-NOESY) and computational studies. which showed the minimum inter-centroid distance between the two aromatic systems to be approximately 3.9 A. Upon addition of acid, the orthoformate/orthoacetate trigger in 6 and 10 was cleaved, which caused a switch of the conformation of the myo-inositol ring to the more stable penta-equatorial chair, leading to separation of the aromatic ester groups and loss of excimer and exciplex fluorescence, respectively. This study provides proof of principle for the development of novel fluorescent molecular probes.     

Synthesis and fluorescence spectra of oxa[3.n]phenanthrenophanes

[reaction: see text]. Novel photostable oxa[3.n](3,9)- and [3.3](3,10)phenanthrenophanes (n = 3, 4) bearing trimethylene-type linkage(s) were successfully synthesized by the intramolecular acid-catalyzed etherification of the corresponding precursor diols. syn-Oxa[3.3](3,10)phenanthrenophane afforded the most red-shifted excimer fluorescence (lambda(max) = 432 nm) among the phenanthrenophanes so far prepared.     

Conformational effects on photophysical characteristics of C5-C5'-linked dihydrothymine dimers in solution

Photophysical characteristics of N-substituted C5-C5'-linked dihydrothymine dimers (1a,b[meso], meso compounds of [5R,5'S]-bi-5,6-dihydrothymines; 1a,b[rac], racemic compounds of [5R,5'R]-bi-5,6-dihydrothymines and [5S,5'S]-bi-5,6-dihydrothymines) in aqueous solution with varying contents of less-polar aprotic solvent such as tetrahydrofuran or dioxane have been investigated by UV-absorption, and steady-state and time-resolved fluorescence spectroscopies. Among the C5-C5'-linked dimers, (5R,5'S)-bi-5,6-dihydro-1-methylthymine (1a[meso]) showed a red-shifted weak UV-absorption band at 270-350 nm and excimer fluorescence emission at lambda max = 370 nm with a quantum yield (phi F) of approximately 0.1 in phosphate buffer (pH < 10) at 293 K. Racemic compound of 5,6-dihydro-1-methylthymine dimer (1a[rac]), meso and racemic compounds of 5,6-dihydro-1,3-dimethylthymine dimers (1b[meso] and 1b[rac]) in phosphate buffer were nonfluorescent under similar conditions. The UV-absorption and fluorescence spectral characteristics of 1a[meso] in aqueous solution were interpreted in terms of intramolecular stacking interactions between the dihydropyrimidine chromophores leading to a preferential "closed-shell" conformation both in the ground state and the excited singlet state. In basic solutions at pH > pKa = 11.7, the fluorescence quantum yield of 1a[meso] decreased due to a dominant "open-shell" conformation resulting from the electrostatic repulsion between the deprotonated dihydrothymine chromophores of 1a[meso] in a dianion form.     

Homogeneous time-resolved fluoroimmunoassay of 3,5,3'-triiodo-l-thyronine in human serum by using europium fluorescence energy transfer

A sensitive homogeneous time-resolved fluoroimmunoassay method for 3,5,3'-triiodo-l-thyronine (T3) based on the fluorescence resonance energy transfer (FRET) from a fluorescent Eu(3+) complex, {[(4,6-dichloro-1,3,5-triazin-2-yl)amino-biphenyl-4'-yl]-2,2':6',2'-terpyridine-6,6'-diyl}bis(methylenenitrilo) tetrakis(acetate)-Eu(3+) (DTBTA-Eu(3+)) (lambda(ex,max)=335nm, lambda(em,max)=615nm), to an organic fluorescence dye Cy5 has been developed. The new assay system combined the use of DTBTA-Eu(3+)-labeled T3-bovine serum albumin (BSA) conjugate and Cy5-labeled anti-T3 monoclonal antibody for a competitive-type immunoassay. After the competitive reactions of DTBTA-Eu(3+)-labeled T3-BSA and T3 sample with Cy5-labeled anti-T3 antibody, the T3 concentration was measured with a time-resolved mode by monitoring the sensitized emission of Cy5 derived from FRET in a homogeneous format. The method gives the detection limit of 0.26ng/ml. The coefficient variations of the method are less than 2.0% and the recoveries are in the range of 80-111% for serum sample measurement. The concentrations of T3 in 30 human serum samples were determined, and the results were compared with those of the independently determined by a radio-immunoassay method. A good correlation was obtained with a correlation coefficient of 0.989.     

Anion dependent structures of luminescent silver(i) complexes

The reaction of AgX, where X = trifluoroacetate (CF(3)CO(2)(-), tfa), nitrate (NO(3)(-)), trifluoromethanesulfonate (triflate, CF(3)SO(3)(-), OTf), hexafluorophosphate (PF(6)(-)), or perchlorate (ClO(4)(-)), with 2,2',3' '-tripyridylamine (tpa) yields five novel silver(I) complexes, which have been structurally characterized. The five complexes have the same 1:1 stoichiometry of Ag/tpa but exhibit different modes of coordination, depending upon the counterion present in the compound. Compound 1, [Ag(tpa)(tfa)](n)(), forms a 1D coordination polymer of [Ag(tpa)(tfa)](2) dimer units linked through bridging tfa counterions. Compound 2, [Ag(tpa)(CH(3)CN)(NO(3))](n), forms a zigzag chain 1D coordination polymer exclusively through Ag-N bonds. In compounds 1 and 2, each tpa ligand is bound to two Ag(I) ions via a 2-py and a 3-py group. Compound 3, [Ag(tpa)(OTf)](n), forms a ribbonlike 1D coordination polymer, in which each tpa ligand binds to three different silver centers via all three pyridyl groups, and the counterion remains coordinated to the Ag(I) center. Compounds 4, [Ag(tpa)(CH(3)CN)](n)(PF(6))(n), and 5, [Ag(tpa)(CH(3)CN)](n)() (ClO(4))(n), display ribbonlike structures resembling that of 3, except that the counterions are not coordinated. All complexes are luminescent in acetonitrile solution, with emission maxima in the near-UV region (lambda(max) = 366, 368, 367, 367, and 368 nm for 1-5, respectively). At 77 K, the emission maxima are red-shifted to lambda(max) = 452, 453, 450, 450, and 454 nm for 1-5, respectively.     

Ground-state conformational equilibrium and photochemical behavior of syn and anti N,N'-dimethyl-N,N'-di-1-naphthylurea protophanes

The structure, spectroscopy, and photochemistry of N,N'-dimethyl-N,N'-di-1-naphthylurea have been investigated and compared to the properties of the corresponding secondary diarylurea N,N'-di-1-naphthylurea and the tertiary mono arylurea N,N,N'-trimethyl-N'-1-naphthylurea. The crystal structures and solution NMR spectra of the tertiary and secondary dinaphthylureas establish that they adopt folded (E,E) and extended (Z,Z) structures, respectively, both in the solid state and in solution. In solution, the tertiary E,E-dinaphthylurea exists as a mixture of syn and anti conformations separated by a barrier of ca. 14 kcal/mol, as determined by variable-temperature (1)H NMR spectroscopy. Computational exploration of the ground-state potential energy surface suggests that the lowest energy pathway for interconversion of the syn and anti conformers requires concurrent rotation about both the nitrogen-naphthalene and the nitrogen-carbonyl single bonds. The tertiary dinaphthylurea exhibits blue-shifted absorption and red-shifted emission attributed to excitonic interactions between the naphthalene rings. The secondary dinaphthylureas and mono naphthylurea have typical naphthalene-like monomer absorption and fluorescence spectra. Dual exponential fluorescence decay is assigned to the two conformers of the tertiary dinaphthylurea. Nonlinear fitting of the fluorescence decay times provides activation parameters for singlet decay of the two conformers. The decay process is attributed to nonsynchronous naphthalene-naphthalene bonding which, in the case of the syn conformer, results in the formation of a [2+2] intramolecular adduct. The preferred E,E conformation and moderate barrier to conformational isomerization make the tertiary dinaphthylurea an attractive building block for larger self-organizing pi-stacked aromatic arrays.     

Reduction reactions of a 1,3,5-triphosphabenzene

The reactions of the triphosphabenzene, 1,3,5-P3C3But3, with LiMH4, M = Al or Ga, lead to the triphosphabicyclo[3.1.0]hexanediyl metallate complexes, [[[Li(OEt2)][MH2(P3C3But3H2)]]2], which give exo- and endo-isomers of a triphosphabicyclo[3.1.0]hexane, P3C3But3H4 upon quenching. The related reaction of [AlH3(NMe3)] with 1,3,5-P3C3But3 affords three identifiable products, viz. a triphosphabicyclo[3.1.0]hexenyl complex, [AlH2(P3C3But3H)(NMe3)], and two triphosphabicyclo[3.1.0]hexanediyl complexes, [AlH(P3C3But3H2)(NMe3)] and [Al2H4(P3C3But3H2)(NMe3)]. In contrast, the reactions of 1,3,5-P3C3But3 with either [GaH3(quin)], quin = quinuclidine, or Me3SnH lead only to the triphosphabicyclo[3.1.0]hexenyl complexes, [GaH2(P3C3But3H)(quin)] and [Me3Sn(P3C3But3H)]. Quenching of the former affords a triphosphabicyclo[3.1.0]hexene, P3C3But3H2, while quenching the latter gives its triphosphacyclohexa-1,4-diene valence isomer. Treatment of 1,3,5-P3C3But3 with "GaI" yields a GaI3 complex of the triphosphahexa-1,4-diene, [GaI3(P3C3But3H2)], whilst treatment with the anionic Ga(I) heterocycle, [:Ga[N(Ar)C(H)]2]-, Ar = C6H3Pri2-2,6, affords the known diphospholyl anion, [1,3-P2C3But3]- via a P-abstraction from the triphosphabenzene. Finally, reaction of the 1,3,5-triphosphacyclohexane, [P(OEt)C(H)(But)]3, with thionyl chloride yields the unusual lambda5, lambda5, lambda5-1,3,5-triphosphacyclohexane, [P(O)(Cl)C(H)(But)]2[P(OEt)(S)C(H)(But)]. Suggestions as to the mechanisms of a number of these reduction reactions are made and the crystal structures of seven compounds are reported.     

Dynamics of energy transfer of a dioxolane-substituted pentacene dispersed in 4,4-bis[N-1-naphthyl-N-phenylamino]biphenyl

We examine the steady-state and time-resolved photoluminescence of guest-host films featuring a dioxolane-substituted pentacene derivative (2,2,10,10-tetraethyl-6,14-bis(triisopropylsilylethynyl)-1,3,9,11-tetraoxadicyclopenta[b,m]pentacene, EtTP-5) dispersed in the hole transporting material (4,4-bis[N-1-naphthyl-N-phenylamino]biphenyl, alpha-NPD). The films show bright red emission (lambda(max) = 640 nm) as a result of efficient F?rster energy transfer from alpha-NPD host molecules to EtTP-5 guest molecules. High absolute photoluminescence (PL) quantum yield (phi(PL) = 76% +/- 4%) and fluorescence lifetime (tau = 18.6 +/- 0.8 ns) were measured at low concentration (0.28 mol % EtTP-5), with moderate PL quenching observed upon increasing the EtTP-5 concentration. The concentrated films (> or = 1.50 mol % EtTP-5) show less evidence of aggregation than previously seen when EtTP-5 was dispersed in tris(quinolin-8-olato)aluminum(III), making alpha-NPD a superior host for the red-emitting EtTP-5.     

Probing the ruthenium-cumulene bonding interaction: synthesis and spectroscopic studies of vinylidene- and allenylidene-ruthenium complexes supported by tetradentate macrocyclic tertiary amine and comparisons with diphosphine analogues of ruthenium and osmium

The synthesis and spectroscopic properties of trans-[Cl(16-TMC)Ru[double bond]C[double bond]CHR]PF(6) (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R = C(6)H(4)X-4, X = H (1), Cl (2), Me (3), OMe (4); R = CHPh(2) (5)), trans-[Cl(16-TMC)Ru[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (X = H (6), Cl (7), Me (8), OMe (9)), and trans-[Cl(dppm)(2)M[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (M = Ru, X = H (10), Cl (11), Me (12); M = Os, X = H (13), Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-C(alpha) and C(alpha)-C(beta) distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two reversible redox couples are observed by cyclic voltammetry for 6-9, with E(1/2) values ranging from -1.19 to -1.42 and 0.49 to 0.70 V vs Cp(2)Fe(+/0), and they are both 0.2-0.3 and 0.1-0.2 V more reducing than those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are dominated by intense high-energy bands at lambda(max) < or = 310 nm (epsilon(max) > or = 10(4) dm(3) mol(-1) cm(-1)), while weak absorptions at lambda(max) > or = 400 nm (epsilon(max) < or = 10(2) dm(3) mol(-1) cm(-1)) are tentatively assigned to d-d transitions. The resonance Raman spectrum of 5 contains a nominal nu(C[double bond]C) stretch mode of the vinylidene ligand at 1629 cm(-1). The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption at lambda(max) = 479-513 nm (epsilon(max) = (2-3) x 10(4) dm(3) mol(-1) cm(-1)). Similar electronic absorption bands have been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm(-1) for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl(NH(3))(4)Ru[double bond]C[double bond]C[double bond]CPh(2)](+) at the MP2 level, and imply that the HOMO is not localized purely on the metal center or allenylidene ligand. The absorption band of 6 at lambda(max) = 479 nm has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nu(C[double bond]C[double bond]C) stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization of the allenylidene ligand is accompanied by rearrangement of the Ru[double bond]C and Ru[bond]N (of 16-TMC) fragments, which supports the existence of bonding interaction between the metal and C[double bond]C[double bond]C unit in the electronic excited state.     

5' modification of duplex DNA with a ruthenium electron donor-acceptor pair using solid-phase DNA synthesis

Incorporation of metalated nucleosides into DNA through covalent modification is crucial to measurement of thermal electron-transfer rates and the dependence of these rates with structure, distance, and position. Here, we report the first synthesis of an electron donor-acceptor pair of 5' metallonucleosides and their subsequent incorporation into oligonucleotides using solid-phase DNA synthesis techniques. Large-scale syntheses of metal-containing oligonucleotides are achieved using 5' modified phosporamidites containing [Ru(acac)(2)(IMPy)](2+) (acac is acetylacetonato; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (3) and [Ru(bpy)(2)(IMPy)](2+) (bpy is 2,2'-bipyridine; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (4). Duplexes formed with the metal-containing oligonucleotides exhibit thermal stability comparable to the corresponding unmetalated duplexes (T(m) of modified duplex = 49 degrees C vs T(m) of unmodified duplex = 47 degrees C). Electrochemical (3, E(1/2) = -0.04 V vs NHE; 4, E(1/2) = 1.12 V vs NHE), absorption (3, lambda(max) = 568, 369 nm; 4, lambda(max) = 480 nm), and emission (4, lambda(max) = 720 nm, tau = 55 ns, Phi = 1.2 x 10(-)(4)) data for the ruthenium-modified nucleosides and oligonucleotides indicate that incorporation into an oligonucleotide does not perturb the electronic properties of the ruthenium complex or the DNA significantly. In addition, the absence of any change in the emission properties upon metalated duplex formation suggests that the [Ru(bpy)(2)(IMPy)](2+)[Ru(acac)(2)(IMPy)](2+) pair will provide a valuable probe for DNA-mediated electron-transfer studies.