A first principles calculations and experimental study of the ground- and excited-state properties of ladder oligo(p-aniline)s

The molecular structure of three ladder oligo(p-aniline)s, 5,11-diethyl-6,12-dimethylindolo[3,2-b]carbazole (DIMER 2P), 14-ethyl-5,8-dihydro-diindolo[3,2-b:2',3'-h]carbazole (TRIMER 2P), and 5,8,14-triethyl-diindolo[3,2-b:2',3'-h]carbazole (TRIMER 3P) were investigated by first principles calculations at the Hartree-Fock (HF6-31G*) and density functional theory (DFTB3LYP6-31G*) levels. It is found that the agreement between theoretical and x-ray geometrical parameters is good and rather similar for both theoretical methods. The nature and the energy of the first two singlet-singlet electronic transitions have been obtained by Zerner intermediate neglect of differential overlap/spectroscopy semiempirical calculations performed on the HF6-31G* and DFTB3LYP6-31G* optimized geometries, as well as time-dependent density functional theory (TDDFT) calculations performed on the DFTB3LYP6-31G* optimized structures. For all the compounds and for all the theoretical approaches, it is observed that the S(1)<--S(0) electronic transition (pipi*) is weakly allowed and polarized along the short axis (y) of the molecule. On the other hand, the S(2)<--S(0) electronic transition of each oligomer possesses a much larger oscillator strength and is polarized along the long (x) molecular axis. It is found that TDDFT calculations provide the best overall agreement between the energies and the corresponding optical transitions obtained from the absorption bands (0-0 peaks) measured in dichloromethane as well as providing a good evaluation of the bathochromic shifts caused by the increase in the conjugation length or by the presence of extra alkyl chains on the nitrogen atoms in TRIMER 3P compared to TRIMER 2P.     

Solid-state static Cu and P CP/MAS NMR, and liquid-state EXAFS studies on copper(I) O,O′-dialkyldithiophosphate cluster compounds: Formation of the copper(I) O,O′-di-iso-amyldithiophosphate cluster compound on the surface of synthetic chalcocite

Polycrystalline octa-nuclear copper(I) O,O′-di-i-propyl- and O,O′-di-i-amyldithiophosphate cluster compounds, {Cu₈[S₂P(OR)₂]₆(μ₈-S)} where R = ⁱPr and ⁱAm, were synthesized and characterized by ³¹P CP/MAS NMR at 8.46 T and static ⁶⁵Cu NMR at multiple magnetic field strengths (7.05, 9.4 and 14.1 T). The symmetries of the electronic environments around the P sites were estimated from the ³¹P chemical shift anisotropy (CSA) parameters, δ_aniso and η. Analyses of the ⁶⁵Cu chemical shift and quadrupolar splitting parameters for these compounds are presented with the data being compared to those for the analogous octa-nuclear cluster compounds with R = ⁿBu and ⁱBu. The ⁶⁵Cu transverse relaxation for the copper sites in {Cu₈[S₂P(OⁱPr)₂]₆(μ₈-S)} and {Cu₈[S₂P(OⁱAm)₂]₆(μ₈-S)} was found to be very different, with a relaxation time, T₂, of 590 μs (Gaussian) and 90 μs (exponential), respectively. The structures of {Cu₄[S₂P(OⁱPr)₂]₄} and {Cu₈[S₂P(OⁱPr)₂]₆(μ₈-S)} cluster compounds in the liquid- and the solid-state were studied by Cu K-edge EXAFS. The disulfide, [S₂P(OⁱAm)₂]₂, was obtained and characterized by ³¹P{¹H} NMR. The interactions of the disulfide and of the potassium O,O′-di-i-amyldithiophosphate salt with the surfaces of synthetic chalcocite (Cu₂S) were probed using solid-state ³¹P NMR spectroscopy and only the presence of copper(I) dithiophosphate species with the {Cu₈[S₂P(OⁱAm)₂]₆(μ₈-S)} structure was observed.     

Intra- and intermolecular fluorescence quenching in 7-(pyridyl)indoles

Three isomeric 7-(pyridyl)indoles reveal very different, solvent-dependent photophysical properties. Due to rapid excited state depopulation involving intramolecular hydrogen bonding, 7-(2′-pyridyl)indole is practically nonfluorescent at room temperature. In nonpolar and polar aprotic solvents, 7-(3′-pyridyl)indole and 7-(4′-pyridyl)indole fluorescence strongly, but the emission is quenched in alcohols. Syn and anti rotameric forms of 7-(3′-pyridyl)indole are detected, each quenched to a different degree. This differential quenching is interpreted as evidence of enhanced S₁ → S₀ internal conversion being more efficient in cyclic solvates, with alcohol molecules forming a bridge between the proton donor and acceptor groups of an excited chromophore.     

Investigation on lanthanide binuclear complexes of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione and 2,2′-bipyridine

The coordination of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione (BPMPPD) and 2,2′-bipyridine (bipy) with lanthanide ions in water-alcohol solution has been studied. Binuclear complexes of the types : Ln₂(BPMPPD)₃(bipy)₂·nH₂O (n = 2 for Y, n = 4 for Eu, Gd, Dy, Ho, Er, Tm and Yb); Ln₂(BPMPPD)₃bipy·nH₂O (n = 10 for La, n = 3 for Pr, Nd, Sm and Tb) were formed. The compounds were characterized by elemental analysis, molar conductance, IR, UV, ¹H NMR spectroscopy, thermogravimetric analysis and fluorescence spectra.     

Synthesis and characterization of new thermally stable copoly(ester–amide)s from diester–dicarboxylic acids

Three new aromatic diester–dicarboxylic acids containing furan rings, namely, benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-phenyl ester-4,4^′-dicarboxylic acid, benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-phenyl ester-3,3^′-dicarboxylic acid and benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-naphthyl ester-2,2^′-dicarboxylic acid were synthesized by the reaction of benzofuro[2,3-b]benzofuran-2,9-dicarbonyl chloride with 4-hydroxybenzoic acid, 3-hydroxybenzoic acid and 3-hydroxy-naphthalene-2-carboxylic acid, respectively. Diester–dicarboxylic acids were characterized by FT-IR and NMR spectroscopy and elemental analyses. Then, these monomers were converted to aromatic copoly(ester–amide)s by their reaction with various aromatic diamines via the direct polycondensation. These polymers were characterized by viscosity measurements, solubility tests, FT-IR, Ultraviolet and ¹H-NMR spectroscopy and thermogravimetry. The polymers with inherent viscosities in the range of 0.16–0.37 dl/g in dimethyl sulfoxide at 30 °C were obtained in high yield. Most of them dissolved readily at room temperature in polar solvents. The synthesized copoly(ester–amide)s possessed glass-transition temperatures from 210–255 °C. The copoly(ester–amide)s exhibited excellent thermal stabilities and had 10% weight loss at temperature above 295 °C under nitrogen atmosphere.     

Low-lying excited singlet states and S2→S0 luminescence of dipyrido[3,4-b: 2,3-d]phenazine

The absorption, fluorescence and excitation fluorescence spectra dipyrido[3,4-b:2,3-d]-phenazine (DPPZ1) have been measured in non-polar and polar matrices at room temperature, and were taken into account to explain the origin of the relatively weak emission of this molecule in both type of environment. The electronic structure of DPPZ1 was calculated using a modified INDO CI method. The geometry optimization has been performed using the MNDO method. According to the spectra and the results of calculations, the lowest excited singlet state S₁ of DPPZ1 molecule is of n,π^*-type and the next one, S₂ state, is of π,π^*-type. The energy gap ΔE_calc is equal 4770 cm⁻¹. The low efficiency of the emission observed in the hydroxylic solvent can be interpreted in terms of thermal quenching of the π,π^*-type fluorescence. However, experimental results obtained suggest that in nonpolar solvents the emission of the molecule examined is an anomalous S₂→S₀ fluorescence.     

Two-colour bound—free—bound spectroscopy of the [E1/2]c6S Rydberg states of CH3I and CD3I

In this resonantly enhanced multiphoton ionization (REMPI) experiment, an extended vibrational progression in the CI stretching mode (v₃) of methyl iodide (-h₃ and -d₃) is observed in the 1 + 1′ excitation of the [1/2] 6s; 0 Rydberg state when the pump photon wavelength lies in the bound → free absorption continuum. This is in contrast with one-colour coherent (non-resonant) two-photon excitation, where the v₃ mode is not excited. By working at several different fixed probe wavelengths and scanning the pump frequency, the relative contributions from the three intermediate repulsive states can be explored through changes in the relative strengths of the Ω = 0 and 1 components of the final Rydberg states. Extensive predissociation in the Rydberg states curtails the vibrational progression.     

Photophysics of inter- and intra-molecularly hydrogen-bonded systems: Computational studies on the pyrrole–pyridine complex and 2(2′-pyridyl)pyrrole

The role of electron and proton transfer processes in the photophysics of hydrogen-bonded molecular systems has been investigated with ab initio electronic-structure calculations. We discuss generic mechanisms of the photophysics of a hydrogen-bonded aromatic pair (pyrrole–pyridine), as well as an intra-molecularly hydrogen-bonded π system composed of the same molecular sub-units (2(2′-pyridyl)pyrrole). The reaction mechanisms are discussed in terms of excited-state minimum-energy paths, conical intersections and the properties of frontier orbitals. A common feature of the photochemistry of these systems is the electron-driven proton transfer (EDPT) mechanism. In the hydrogen-bonded complex, a highly polar charge transfer state of ¹ππ^* character drives the proton transfer, which leads to a conical intersection of the S₁ and S₀ surfaces and thus ultrafast internal conversion. In 2(2′-pyridyl)pyrrole, out-of-plane torsion is additionally needed for barrierless access to the S₁–S₀ conical intersection. It is pointed out that the EDPT process plays an essential role in the fluorescence quenching in hydrogen-bonded aromatic complexes, the function of organic photostabilizers, and the photostability of biological molecules.     

Effect of solvent on the subnanosecond decay of the second excited singlet state of tetramethylindanethione

The S₂ → S₀ fluorescence spectra and quantum yields and the S₂ lifetimes of 2,2,3,3-tetramethylindanethione (TMIT) have been measured in several solvents using a synchronously pumped picosecond dye laser excitation system. The S₂ nonradiative decay rate is markedly solvent dependent. In inert perfluoroalkane solvents remarkably large S₂-S₀ fluorescence quantum yields (θ_f = 0.14) and long S₂ lifetimes (τ = 880 ps) are measured. Hydrocarbons are efficient excited-state quenchers.     

Novel ferroelectric liquid crystals based on fused thieno[3,2-b]furan and thieno[3,2-b]thiophene cores

Several series of new benzofused thieno[3,2-b]furan- and thieno[3,2-b]thiophene-based derivatives have been synthesized and their mesomorphic properties investigated. All the studied compounds exhibit a SmC* phase with very wide temperature interval. Additionally, some types of the compounds show the cholesteric, SmA or blue phase. In the ferroelectric SmC* phase we evaluated physical properties of relevance for possible applications.     

H, C, N NMR, ESI mass spectral and single crystal X-ray structural characterization of three spiro[pyrrolidine-2,3′-oxindoles]

Three spiro[pyrrolidine-2,3′-oxindoles], 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-phenyl-spiro[3H-indole-3,3′-[3H]-pyrrolizine]-2′-carboxylic acid methyl ester (1), 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-phenyl-spiro[3H-indole-3, 3′-[3H]-pyrrolizine] (2) and 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-(4″-chlorophenyl)-spiro[3H-indole-3,3′-[3H]-pyrrolizine] (3) have been synthesized and their ¹H, ¹³C and ¹⁵N spectra assigned. The chemical shift assignments are based on Pulsed Field Gradient (PFG) Double Quantum Filter (DQF) ¹H, ¹H correlation spectroscopy (COSY), PFG ¹H, ¹³C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG ¹H,X (X = ¹³C and ¹⁵N) Heteronuclear Multiple Bond Correlation (HMBC) experiments. The single crystal X-ray structures of 1–3 have been determined. Compounds 1 and 2 crystallized in monoclinic space group C2/c and compound 3 in monoclinic space group P2₁/c, respectively. Also the ESI-TOF MS data of 1–3 are given.     

A comparative electron correlation treatment in H(2)S-benzene dimer with DFT and wavefunction-based ab initio methods

The S₀ (X¹A′), T₁ (a³A″), S₁ (A¹A″), T₂ (b³A′), and S₂ (B¹A′) states of the (trans-)HONO molecule were studied by using the CASSCF and CASPT2 methods. The CASPT2(//CASPT2) adiabatic and vertical excitation energy values are in good agreement with available experimental data. The CASPT2//CASSCF potential energy curves (PECs) calculations indicate that: (i) all the five states correlate with the products of OH (X²Π) + NO (X²Π); (ii) along each of the T₁, S₁, and T₂ PECs there is a minimum followed by a transition state (barrier); and (iii) the repulsive S₂ PEC crosses the T₂, S₁, and T₁ PECs. The geometries and relative energies for the stationary points along these PECs were calculated at the CASPT2(//CASPT2) level, and the calculations predict that the barrier height value for S₁ is negligibly small (0.0018 eV).     

Tris-chelate complexes with chiral ligands: In search of diastereoisomeric selectivity with remote stereogenic centres

The chiral ligands, 4,4′-bis{(1S,2R,4S)-(−)-bornyloxy}-2,2′-bipyridine, (1S,2R,4S)-1, and 4,4′-bis{(1R,2S,4R)-(+)-bornyloxy}-2,2′-bipyridine, (1R,2S,4R)-1, have been prepared and characterized by spectroscopic techniques and, for (1S,2R,4S)-1, by single crystal X-ray diffraction. Despite the use of enantiomerically pure ligands, the formation of the complexes [Fe((1S,2R,4S)-1)₃]²⁺, [Ru((1S,2R,4S)-1)₃]²⁺, [Ru((1S,2R,4S)-1)(bpy)₂]²⁺ and [Ru((1R,2S,4R)-1)(bpy)₂]²⁺ proceeds without preference for either the Δ or Λ-diastereoisomers.     

Solvatochromism of 3-[2-(aryl)benzoxazol-5-yl]alanine derivatives

The photophysical properties of N-Boc-3-[2-(9-anthryl)benzoxazol-5-yl]-l-alanine methyl ester (BoxAnt) and N-Boc-3-[2-[4-(9′-(10′-butyl)anthryl)phenyl]benzoxazol-5-yl]-l-alanine methyl ester (BoxPhAnt) were studied in a series of solvents. Their absorption spectra are less sensitive to the solvent polarity than the corresponding fluorescence spectra which show a pronounced solvatochromic effect leading to large Stokes shifts. Using an efficient solvatochromic method, based on the empirical solvent polarity parameter , a large change of the dipole moment on excitation for BoxPhAnt has been found. From an analysis of the solvatochromic behaviour of the absorption and fluorescence spectra in terms of bulk solvent polarity functions, f(_r, n) and g(n), a larger excited-state dipole moment (about 8 D, ψ = 56) was obtained for BoxPhAnt than for BoxAnt (about 3 D, ψ = 0). Both applied methods gave similar values of the excited-state dipole moments for both compounds studied.     

Role of homogeneous solvents on photophysics of 3-pyrazolyl-2-pyrazoline derivative

S₀ → S₁ and S₀ → S₂ electronic transitions have been observed in UV–Visible absorption spectroscopy of 3-pyrazolyl-2-pyrazoline (PZ) in different homogeneous solvents. Radiative emissions and relaxation processes from S₁ and S₂ states of PZ have been resolved in water, ethylene glycol and glycerol whereas in polar aprotic and protic solvents the radiative transitions have been observed from S₁ state. The S₂–S₁ electronic energy spacing has been calculated from the absorption maxima of the S₀ → S₂ transitions and fluorescence maxima of the S₁ → S₀ transitions. Solute–solvent interactions have been established to rationalize the photophysical modification of PZ in H-bonding solvents.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

Coherence retention during rotationally inelastic collisions of selectively excited diatomic sulfur

Hanle effect broadening rates have been measured for selectively excited S₂ (B ³Σ⁻_u, υ′ = 4, N′ = 40, J′ = 41) with a variety of collision partners. In the cases of N₂ and the rare gases, a comparison with previously determined rotational and vibrational energy transfer rates shows that coherence is retained throughout transfer collisions. This is confirmed by direct observation of the Hanle effect in nearby rotational levels populated by collision, using a monochromator to disperse the fluorescence. These results indicate that collisions which change the magnitude of the rotational angular momentum (even by several quanta) do not severely alter its orientation.     

Relative quantum yield of the S2 → S1 fluorescence from azulene

The quantum yield ratio r = φ_{2 → 0}/φ_{2 → 1} of the S₂ → S₀ and S₂ → S₁ fluorescences from azulene has been redetermined. With azulene in isopentane at 190 K, r = 455 ± 100. This value agrees with the lower limit, given by Huppert, Jortner and Rentzepis, but is an order of magnitude lower than that given by Gillispie and Lim.     

Synthesis, crystal structure and third-order non-linear optical property of heterobimetallic cluster compound [MoOICu3S3(2,2′-bipy)2]

Nest-shaped cluster [MoOICu₃S₃(2,2′-bipy)₂] (1) was synthesized by the treatment of (NH₄)₂MoS₄, CuI, (n-Bu)₄NI, and 2,2′-bipyridine (2,2′-bipy) through a solid-state reaction. It crystallizes in monoclinic space group P2₁/n, a=9.591(2) Å, b=14.820(3) Å, c=17.951(4) Å, β=91.98(2)°, V=2549.9(10) ų, and Z=4. The nest-shaped cluster was obtained for the first time with a neutral skeleton containing 2,2′-bipy ligand. The non-linear optical (NLO) property of [MoOICu₃S₃(2,2′-bipy)₂] in DMF solution was measured by using a Z-scan technique with 15 ns and 532 nm laser pulses. The cluster has large third-order NLO absorption and the third-order NLO refraction, its ₂ and n₂ values were calculated as 6.2×10⁻¹⁰ and −3.8×10⁻¹⁷ m² W⁻¹ in a 3.7×10⁻⁴ M DMF solution.     

Perfluoromethyl—element-liganden : XX. Bildung von heteronuclearen zweikernkomplexen des typs mm′(CO)nXY (M = Mn; M′ = Re, Co)

The reactions of MnRe(CO)₁₀ with As₂(CF₃)₄ and MnCo(CO)₉ with P₂(CF₃)₄, As₂(CF₃)₄, S₂(CF₃)₂, Se₂(CF₃)₂, (CF₃)₂EI (E = P, As), (CF₃)₂AsH, (CF₃)₂AsE′CF₃ (E′ = S, Se), (CF₃)₂PSeCF₃, Me₂AsI and (CF₃)₂PPMe₂, respectively, have been studied under various conditions. Besides already known mono- and binuclear compounds the heteronuclear complexes MnRe(CO)₈[As(CF₃)₂]₂ and MnCo(CO)₇[E(CF₃)₂]₂ (E = P, As) are formed. The reactions proceed via cleavage of the M---M′ bond and formation of the mononuclear species Mn(CO)₅X and M′(CO)_nY (M′ = Re, n = 5; M′ = Co, n = 4).