Two-photon absorption study of Zn(II)tetraphenylporphin: Role of a higher excited singlet state of gerade symmetry

The S₂ state fluorescence of Zn(II)tetraphenylporphin has been studied by using two-photon absorption and optical—optical double-resonance techniques. The main process to populate the S₂ state was found to be a stepwise two-photon absorption to the S_nstate through the S₁ state. The large absorption cross section of the S_n ← S₁ transition (6.8 × 10^?16 cm² molecule^?1) at 540 nm suggests that there exists a higher excited singlet state of gerade parity.     

Temperature effect on inverse (Tn → S1) intersystem crossing

The temperature effects on the quantum yields φ_TS of the inverse (T_n → S₁ intersystem crossings of anthracene, 9-methylanthracene and acridine are studied by the stepwise two-photon excitation technique. Φ_TS of anthracene in ethanol increases with increasing temperature, while that of 9-methylanthracene does not depend on temperature, Φ_TS of acridine in alkaline water decreases with increasing temperature.     

Vibronic coupling of pyrene in the first ππ* excited state

The two-photon fluorescence excitation spectrum of pyrene in n-hexane and n-heptane matrices has been measured at 10 K in the region of the first electronic transition (26800–30200 cm^?1). The spectrum consists of a rich number of sharp bands, being in general better resolved in n-hexane than in n-heptane matrix. Shpol'skii multiplets have been observed for the most intense bands. A strong two-photon band dominates the spectrum = 1495 cm^?1 from the 0—0 line and was assigned to B_1u × b_1u = A_g symmetry. Other weaker vibronic origins occur in the spectrum which were correlated to vibrational modes of b_1u, b_2u, b_3u and a_u symmetry. Intense vibronic bands are observed close to the origin of the second electronic transition and were interpreted as combination bands of B_1u × b_1u × b_3g symmetry. A two-photon vibronic theory to account for their intensity is proposed where the electronic moment is linearly expanded in powers of the nuclear displacements.     

Resonant two-photon two-color photoionization (R2P2CI) spectra of aniline-Ar n clusters: Isomer strutures and solvent shifts

We present resonant two-photon two-color photoionization (R2P2CI) spectra of a series of Aniline-Ar _n complexes (n=1?6). An apparently anomalous blue shifted spectra for An-Ar₃ is explained by a modified spectral shift additivity rule which assigns different shifts to different relative positions of the Ar with respect to aniline. Evidence is presented for the existence of several isomers of clusters withn≧2. It is shown that, by changing the nucleation conditions, it is possible to control the relative populations of the various isomers.     

Broadening and shift of thalliumnP 1/2,3/2 states (n=6–10) perturbed by noble gases

Impact broadening and shift of the transitions Tl 6P _1/2?nP _1/2,3/2 (n=7, 9, 10) and 6P _3/2?9P _{1/2, 3/2} are measured by high resolution Doppler-free two-photon spectroscopy. For excited states with small principal quantum numbers the results are in accord with values obtained fromC ₆-C ₈-C ₁₂ potentials calculated semiempirically. For intermediate principal quantum numbers the experiments show that the elastic scattering of the valence electron at the noble gas atom must be considered additionally. The experimental shift rates ofP _1/2 states are found to be larger than ofP _3/2 states. Furthermore, the line shifts of the one- and two-photon transitions concerning the 6P _1/2, 6P _3/2, 9P _1/2, 9P _3/2, 7S _1/2 states show that the contribution of the lower level of the transition must be considered too.     

New synthesis and thermal studies of palladacycloalkanes and their precursors

A series of new palladacycloalkanes of formula cis-[PdL₂(CH₂)_n] (9. n = 6, L = PPh₃; 10. n = 6, L₂ = dppe; 11. n = 8, L = PPh₃; 12. n = 8, L₂ = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-[PdL₂((CH₂)_nCHCH₂)₂] (1. n = 2, L = PPh₃, 2. n = 2, L₂ = dppe, 3. n = 3, L = PPh₃, 4. n = 3, L₂ = dppe) were allowed to react with Grubb’s 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL₂(CH₂)_nCHCH(CH₂)_n] (5. n = 2, L = PPh₃, 6. n = 2, L₂ = dppe, 7. n = 3, L = PPh₃, 8. n = 3, L₂ = dppe), which were then hydrogenated to the palladacycloalkanes, 9-12. In the second route, the di-Grignard reagents BrMg(CH₂)_nMgBr (n = 6, 8) were reacted with the palladium complex [PdCl₂(COD)] followed by immediate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9-12 and the main organic products shown to be 1-alkenes and 2-alkenes.     

Synthesis and surface activities of organic solvent-soluble fluorinated surfactants

A variety of fluorinated surfactants soluble in organic solvent were prepared, including C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8, 10), C₈F₁₇SO₂NHR (R = C₆H₁₁, C₆H₅), C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) and C₈F₁₇SO₂NH(CH₂)_nNHO₂SC₈F₁₇ (n = 6, 10). Their surface activities in various organic solvents were determined by surface tension measurement. The results showed that these fluorinated surfactants can reduce the surface tension of both polar and non-polar organic solvents. In general, organic solvents with strong polarity or long alkyl chain are beneficial to increase the surface activity of these polar fluorinated surfactants. By comparing fluorinated surfactants with the same fluorocarbon segment and connecting group, C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) showed lower surface activity in organic solvents than C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8) with an equal carbon number of the solvophilic group. Through surface tension vs. concentration curves given for N-octyl perfluorooctanesulfonamide in various organic solvents, a break point like the critical micelle concentration of ordinary surfactants in aqueous solutions was observed, and the effect of the different types of organic solvents on adsorption and aggregation behavior was also studied.     

Two-photon absorption of dissociating TLI in strong laser fields

In a strong laser field (I=2 GW/cm²) TlI is dissociated by a two-photon process and the Tl fragment is detected state specifically. The yield of Tl 6p ² P _3/2 (Tl*) is measured as a function of the dissociation wavelength (480 nm–540 nm). If the dissociation wavelength is close to two-photon transitions of the Tl atom from 6p ² P _3/2 to np² P _1/2,3/2 or mf² F _5/2,7/2,n=10 ... 15,m=7 ... 12 dips in the yield are observed. These dips show a significant asymmetric broadening, compared to a free atomic transition and the observation is interpreted as an absorption process of the transient state of dissociating TlI during the laser pulse. By applying the Landau-Zener approximation for the potential crossing of dressed molecular states, we are able to describe the broadening and the power density dependence of the observations. Simulations show that the asymmetry is determined by the difference potential of the electronic states which are coupled by the laser field.     

Synthesis and characterization of a new class of polyfluorinated alkanes: tetrakis(perfluoroalkyl)alkane

The synthesis and physico-chemical characterization of 1,1,2,2-tetrakis(perfluoroalkyl-methylene)ethane {[F(CF₂)_nCH₂]₂CH}₂ (n=6, TK6; n=8, TK8) are reported. The synthesis consists of four steps: (1) addition of allyl alcohol to a perfluoroalkyl iodide, F(CF₂)_nI (n=6,8) to give the corresponding iodo-adduct; (2) dehalogenation of the adduct by treatment with zinc in aqueous acetic acid, yielding 3-perfluoro-n-alkyl-1-propene; (3) addition of 3-perfluoro-n-alkyl-l-propene to perfluoroalkyl iodide, F(CF₂)_nI (n=6,8) to give 1,3-perfluoro-n-alkyl-2-iodo-propane; (4) coupling of 1,3-perfluoro-n-alkyl-2-iodo-propane by zinc in acetic anhydride giving the final products. TK6 and TK8 are characterized by very low surface tension values and exhibit very good properties as potential ski-waxes.     

Practice of fluorous biphase chemistry: convenient synthesis of novel fluorophilic ethers via a Mitsunobu reaction

The evolution of the term fluorous is addressed first, then a concise terminology is proposed, including fluorous partition coefficient, specific fluorophilicity and fluorousness. Some examples are shown for the design of higher generation fluorophilic molecules, involving Class I to Class III ponytails. Fluorophilic ethers of the structure of ArC(CF₃)₂O(CH₂)_m(CF₂)_nF (m=1, n=1, 7; m=3, n=8) are obtained in high yields, when 2-aryl-1,1,1,3,3,3-hexafluoro-propanols are reacted either with trifluoroethyl- and 1H,1H-perfluorooctyl triflates (NaH/DMF, Williamson ether synthesis) or with 3-perfluorooctyl-propanol (Ph₃P/EtO₂CNNCO₂Et/PhCF₃, Mitsunobu reaction), respectively. Fluorophilic phenol- and perfluoro-tert-butyl ethers can also be prepared effectively by the latter method. In case of higher homologues (n=7, 8) product isolation can be facilitated using fluorous extraction (C₆F₁₄/CH₃OH). Specific fluorophilicity values of target molecules are estimated using a 2D method and compared with experimentally determined ones.     

One- and two-photon laser photolysis of dicyanoacetylene

The time-resolved electronic absorption spectra of CN radical, resulting from the laser photolysis of dicyanoacetylene (DCA) at 193 and 248 nm, were analyzed. Detection of the other probable photodissociation product—C₃N radical—has not been possible. Photolysis at 193 nm produces CN both in the X²∑⁺ and in the A²Π_i manifolds, the latter—probably populated via a two-photon process—being revealed by a delayed (collision-induced) transfer to the higher vibrational levels of the ground electronic state. Photolysis at 248 nm is an efficient two-photon process. A simplified kinetic model for the decay of CN radical has been proposed and the rate constant for the CN + DCA reaction was derived. Semiempirical INDO/S CI-1 calculations of the DCA valence shell electronic transitions were performed.     

Electron transfer from laser excited rydberg atoms to molecules. Absolute rate constants at low and intermediate principal quantum numbers

Using mass spectrometric detection of positive and negative ions, we have investigated ionizing reactions of Ne(ns,nd) Rydberg atoms, efficiently excited by resonant two-photon excitation of metastable Ne(3s ³ P ₂) atoms, with electron attaching moleculesBC (BC=SF₆, CCl₄, CS₂, O₂) at thermal collision energies. Absolute rate constants have been determined in the range of low and intermediate principal quantum numbersn(5≦n?30) by utilizing the photoionization signal caused by room temperature black-body radiation and the loss of Ne(3s ³ P ₂) atoms, associated with the laser excitation. Substantially differentn-dependences of the electron transfer cross section have been found for the larger molecules (BC = SF₆, CCl₄) and the smaller molecules (BC = CS₂, O₂). Simple model calculations have been performed to gain new insight into the dynamics of the electron transfer process; forBC = SF₆, our results at lown(5 ≦n ≦ 10) suggest that internal energy conversion in the Coulombic complex Ne⁺ — SF ₆ ^? is important for the formation of the detected ions.     

Laser multiphoton ionization of aromatic molecules in nonpolar liquids

The laser multiphoton ionization (MPI) of fluoranthene in tetramethylsilane (TMS) and of azulene in n-tridecane, n-pentane, 2,2,4,4-tetramethylpentane, TMS and tetramethyltin is reported. Three distinct types of MPI mechanisms have been identified: two-photon ionization, stepwise three-photon ionization and mixed two- and three-photon ionization. The stepwise three-photon process consists of two-photon excitation, relaxation to a lower lying excited state with a lifetime comparable to the laser pulse duration (for azulene this state is the S₂ while for fluoranthene both the S₁ and S₂ states) and subsequent ionization with the absorption of a third photon. The ionization threshold of azulene in each liquid has been determined and found to vary linearly with the V₀ of the liquid.     

The System Polyacrylamide—Water

The system polyacrylamide (PAA) — water at 0<n<25 (n=H₂O/(-C(O)NH₂)) was investigated. In air of 100% humidity at 292 K, at equilibrium n≈18. The differential heat of water vapour sorption decreases from 56 kJ mol¹ (initial heat) to the heat of water vaporization (Q _L) at n≈0.5, and then up to n=18 it passes through several maxima and minima in the vicinity of Q _L; at n>18, it is equal to Q _L. The mechanism of the gradual solution of PAA is proposed. As the system sorbs water, it passes through the consecutive stages of formation of the clathrate-like compounds AG·2H₂O and AG·(17?18)H₂O (AG is an amido group of PAA) with subsequent formation of a perfect aqueous solution of compound I.     

Synthesis,properties, and reactions of enantiomerically pure,chiral fluorous phosphines of the formula (menthyl)P(CH2CH2(CF2)n−1CF3)2 (n=6, 8)

Reactions of (menthyl)PH₂ and H₂CCHR_f6 (menthyl=1R,3R,4S; R_fn=(CF₂)_n−1CF₃) or H₂CCHR_f8 (AIBN, refluxing THF) give (menthyl)PH(CH₂CH₂R_fn) and then (menthyl)P(CH₂CH₂R_fn)₂ (n=6, 7; n=8, 8), but with purification or other difficulties at each stage. Reactions of (menthyl)PCl₂ with IMgCH₂CH₂R_fn give, under careful conditions, analytically pure 7 or 8 in 28–32% yields after distillation. Some R_fn(CH₂)₄R_fn also form. These represent the first chiral (and non-racemic) fluorous phosphines. Reactions of 7 or 8 with [Ir(COD)Cl]₂ and CO give trans-[(menthyl)P(CH₂CH₂R_fn)₂]₂Ir(Cl)(CO) (n=6, 71%; 8, 51%) as analytically pure yellow oils. Their IR ν_CO values show the donor/acceptor properties of 7 and 8 to be intermediate between those of P((CH₂)₃R_f8)₃ and P((CH₂)₄R_f8)₃. The CF₃C₆F₁₁:toluene partition coefficients of 7 and 8 (27°C, 78.4:21.6 and 93.7:6.3) are distinctly lower than those of P((CH₂)₂R_fn)₃ (n=6, 98.8:1.2; n=8, >99.7:<0.3), reflecting the replacement of a linear C₈–C₁₀ group that is ca. 75–80% fluorinated by a cyclic C₁₀ terpenyl group. Reactions of 7 or 8 with [Rh(COD)Cl]₂ give [(menthyl)P(CH₂CH₂R_fn)₂]Rh(Cl)(COD) (n=6, 69%; 8, 70%) as orange crystallizable oils.     

The route to MBxNyCz molecular wheels: II. Results using accurate functionals and basis sets

Applying ab initio quantum chemical methods, molecular wheels composed of metal and light atoms were investigated. High quality basis sets 6-31G*, TZPV, and cc-pVTZ as well as exchange and non-local correlation functionals B3LYP, BP86 and B3P86 were used. The ground-state energy and structures of cyclic planar and pyramidal clusters TiB_n (for n = 3–10) were computed. In addition, the relative stability and electronic structures of molecular wheels TiB_xN_yC_z (for x, y, z = 0–10) and MB_nC_10−n (for n = 2 to 5 and M = Sc to Zn) were determined. This paper sustains a follow-up study to the previous one of Boustani and Pandey [Solid State Sci. 14 (2012) 1591], in which the calculations were carried out at the HF-SCF/STO3G/6-31G level of theory to determine the initial stability and properties. The results show that there is a competition between the 2D planar and the 3D pyramidal TiB_n clusters (for n = 3–8). Different isomers of TiB₁₀ clusters were also studied and a structural transition of 3D-isomer into 2D-wheel is presented. Substitution boron in TiB₁₀ by carbon or/and nitrogen atoms enhances the stability and leads toward the most stable wheel TiB₃C₇. Furthermore, the computations show that Sc, Ti and V at the center of the molecular wheels are energetically favored over other transition metal atoms of the first row.     

Formation and structural refinements of tunneled intergrowth phases in the Ga2O3-In2O3-SnO2-TiO2 system

Over 100 samples were prepared as (Ga,In)₄(Sn,Ti)_n−4O_2n−2, n=6, 7, and 9 by solid-state reaction at 1400 °C and characterized by X-ray diffraction. Nominally phase-pure beta-gallia-rutile intergrowths were observed in samples prepared with n=9 (0.17?x?0.35 and 0?y?0.4) as well as in a few samples prepared with n=6 and 7. Rietveld analysis of neutron time-of-flight powder diffraction data were conducted for three phase-pure samples. The n=6 phase Ga_3.24In_0.76Sn_1.6Ti_0.4O₁₀ is monoclinic, P2/m, with Z=2 and a=11.5934(3) Å, b=3.12529(9) Å, c=10.6549(3) Å, β=99.146(1)°. The n=7 phase Ga_3.24In_0.76Sn_2.4Ti_0.6O₁₂ is monoclinic, C2/m, with Z=2 and a=14.2644(1) Å, b=3.12751(2) Å, c=10.6251(8) Å, β=108.405(1)°. The n=9 phase Ga_3.16In_0.84Sn₄TiO₁₆ is monoclinic, C2/m, with Z=2 a=18.1754(2) Å, b=3.13388(3) Å, c=10.60671(9) Å, β=102.657(1)°. All of the structures are similar in that they possess distorted hexagonal tunnels parallel to the [010] vector.     

Reversible crotylstannation of carbonyl compounds. Crotylstannation ability of Bu3-nClnSnCH2CHCHCH3 (n = 0, 1, 2) compounds towards acetone and benzaldehyde and 13C NMR characterization

The crotylstannation reaction:

has been found to be reversible. The compounds trans/cis-Bu_3-nCl_n SnCH₂CH= CHCH₃ (n = 0, 1, 2) have been prepared by elimination reactions of organostannoxy compounds,Bu_3?nCl_nSn—O—C(Me)(i-Pr)CH(Me)CHCH2, which were synthesized by means of transalkoxylation between Bu_3-nCI_nSn(OMe) compounds and threo/erithro-2,3,4-trimethyl-5-hexen-3-ol. Under the conditions used the elimination occurs stereospecifically and with complete allylic rearrangement. The ability of the organostannoxy compounds to yield crotyl butylchlorotins via elimination increases in the order, Bu₃Sn—O—C < Bu₂ClSn—O—C < BuCI₂Sn—O—C. In the addition reactions, the sequence of increasing reactivity is Bu₃SnCrot < CIBu₂SnCrot < CI₂BuSnCrot (Crot = crotyl). The ¹³C NMR spectra of the compounds made reveal that the chemical shifts of the allylic carbon atoms are related to the inductive effects of the chloro-substituents.     

The measurements ofn 2D levels and fine structure intervals of cesium

The transitions ofn ² D6² S,F=4, of the cesium atom are studied by Doppler-free two-photon spectroscopy combined with a thermionic diode detector. Progress in overcoming the influence of single-photon background of the molecular Cs₂, the levels and fine structure intervals ofn ² D withn=54–70 are obtained.This work was supported by the NSFC (No. 1880757)