Photoisomerization Paths of α,ω-Diphenylpolyenes: Reaction Rate Dependence on Temperature, Excitation Wavelength, and Deuteration.

The photoisomerization rate of -stilbene (tS) and trans-trans-diphenylbutadiene (ttD) is studied in solution and compared to that in jet/gas. Rice-Ramsperger-Kassel-Marcus (RRKM) theory correctly predicts the tS rate in jet, = exp(-/) with = 1398 cm, and = 1.8 ps corresponding to frequency ν = 60 cm of the reactive mode, being the molecular temperature.

Effect of exohedral functionalization on the magnetic properties in the dysprosium-containing endohedral fullerene DyScN@C(CF).

We present a quantum-chemical study of the effect of exohedral functionalization with a CF group on the lowest electronic states and the zero-field splitting pattern in a potential single-molecule magnet (SMM) compound DyScN@C(CF). Multiconfiguration perturbational methodology is applied to various spin states of the endohedral compound, comparing different active spaces and state-averaging schemes in order to check for the possible involvement of orbitals other than 4f-Dy in the nondynamical electronic correlation and to suggest the most appropriate computational parameters. Combining the spin-orbit coupling calculations with perturbational corrections, we demonstrate that the interactions within the endohedral cluster and with the fullerene cage exert only a small effect on the non-relativistic approximation to the electronic states of the Dy ion, yet they are significant enough to alter the parameters of zero-field splitting depending on the orientation of the DyScN cluster inside the fullerene cage.

Nonclassical C and C Chlorofullerenes via Complex Chlorination-Promoted Skeletal Transformations of IPR Isomers of C and C.

Upon high-temperature (340-360 °C) chlorination with VCl, an isolated-pentagon-rule (IPR) -C(33) fullerene is just chlorinated to C(33)Cl and C(33)Cl, but a VCl/SbCl mixture promotes a five-step cage transformation to nonclassical C(2)Cl with two heptagons and five pairs of fused pentagons. Another chlorination-promoted seven-step transformation of an IPR fullerene removes as many as four C2 fragments from C to give a nonclassical C(1)Cl with cage heptagon and six fused pairs of pentagons. We discuss the driving forces behind the observed transformations and probable detailed pathways thereof.

Oxidative cage opening in the C fullerene facilitated by preceding trifluoromethylation.

Two novel derivatives of the C fullerene with 9- and 10-membered cage openings were obtained by means of oxidation and decarbonylation of C(CF). The major product, C(O)(CF)O, features a cleaved C-C bond transformed into two carbonyl functions plus an ether bridge. The second product, CO(CF)O, has one of the carbonyls replaced with another ether bridge.

Dimeric and 1D polymeric low-chlorinated C fullerenes, (CCl) and (CCl).

Low-chlorinated fullerenes, dimeric (CCl) and one-dimensional, polymeric (CCl), were obtained by high-temperature (270 °C) chlorination of C with a SbCl/SbCl mixture, as revealed by X-ray crystallography. The compounds were characterized by IR and Raman spectroscopy and theoretical calculations. This is the first observation of a fullerene polymer with single C-C bonding and neutral building blocks.

/ photoisomerization pathway in pristine and fluorinated di(3-furyl)ethenes.

We report an XMCQDPT2 study of the / photoisomerization in a series of fluorinated di(3-furyl)ethenes (3DFEs). Upon excitation, pristine and low-fluorinated 3DFE show conventional behavior of many diarylethenes: unhindered twisting motion toward the pyramidalized zwitterionic state where relaxation to the ground state occurs. However, deep fluorination of 3DFEs can hamper -to- isomerization by giving rise to an alternative excited-state relaxation pathway: an out-of-plane motion of a ring fluorine atom.

Crippling the C fullerene: non-classical CCl(OH) and CCl(OH) with three heptagons and only fused pentagons chlorination-promoted skeletal transformations.

High-temperature (440 °C) chlorination of C with SbCl promotes Stone-Wales transformations and loss of the C fragment, which results in a non-classical CCl partially hydrolyzed to CCl(OH) and CCl(OH). X-ray diffraction reveals an unprecedented C cage with three heptagons and 15 pentagons arranged in fused pairs and triples. The shortest possible transformation pathways include one C loss step and four Stone-Wales transformation steps.

Dissociative Electron Attachment to Hexachlorobenzene.

Gas phase molecules of hexachlorobenzene (C Cl ) were investigated by means of dissociative electron attachment spectroscopy (DEAS). Three channels of molecular negative ions decay have been identified: abstraction of Cl and Cl as well as electron detachment (τ ∼250 μs at 343 K). All three channels exhibit temperature dependence.

Regioselective CF functionalization of ScN@(5)-C.

We report the first synthesis and computational study of ScN@C(CF) - an analog of the previously reported ScN@C(CF) with a less common carbon cage whose chemical properties presently remain far less studied. ScN@C appears to be considerably more reactive toward CF addition than ScN@C and somewhat more reactive than C. Even though the less symmetric (5)-C carbon cage offers far broader opportunities for isomerism than -C, CF addition to ScN@C proceeds regioselectively, similarly to other common fullerene reactions.

Substitution pattern dependent behavior of the singlet excited states in symmetrically fluorinated biphenyls.

Biphenyls are important basic chromophore systems that offer a possibility to study the effects of chemical substitution on the lower-lying excited states without complications from photoisomerization or other side processes. For several symmetric biphenyls, pristine biphenyl (bP0), 4,4'-difluorobiphenyl (bP2), 2,3,5,6,2',3',5',6'-octafluorobiphenyl (bP8), and perfluorobiphenyl (bP10), we report stationary and ultrafast solution-phase spectra rationalized with the aid of computations by means of the XMCQDPT2 multi-configuration perturbation theory and TDDFT. Polyfluorination tends to broaden the gap between the nearly degenerate S + S pair of states and the S state in bP8 and bP10, yet relaxation from any sheet of the S-S manifold leads through a system of state crossings to the same stationary points in S.

Electrochemically Induced Dimerization of -C(CF) Trifluoromethylated Fullerene.

We report a comprehensive study of a novel isomer of C(CF), -C(CF), whose electrochemical behavior differs from most of the other trifluoromethylated fullerenes. The addition pattern of -C(CF) is established by means of F-F COSY NMR spectroscopy and DFT calculations. Like -C(CF), the new isomer -C(CF) undergoes dimerization to the [C(CF)] upon single-electron reduction.

Addition of CF group to endohedral fullerene ScN@I-C.

We report the first successful synthesis of a CF derivative of the stable endohedral fullerene ScN@I-C. Reaction with CFClCOONa yields a single C-symmetric ScN@C(CF) adduct where the CF group is inserted into a [6,6]-bond and opens it to 2.3 Å between the bridgehead carbon atoms.

Evaluating the Solvent Stark Effect from Temperature-Dependent Solvatochromic Shifts of Anthracene.

The solvent Stark effect on the spectral shifts of anthracene is studied with temperature-dependent solvatochromic measurements. The Stark contribution Δv to the absorption shift Δv in polar solvents is measured to be Δv =(53±35) cm , in reasonable agreement with dielectric continuum theory estimate of 28 cm , whereas the major shift Δv ∼300 cm presumably originates from the solute quadrupole. We pay attention to the accurate correction of Δv for the nonpolar contribution that is crucial when the shifts are modest in magnitude.

Dissociative Electron Attachment to 2,3,6,7,10,11-Hexabromotriphenylene.

2,3,6,7,10,11-Hexabromotriphenylene (HBTP) and 2,3,6,7,10-pentabromotriphenylene (PBTP) were investigated by means of dissociative electron attachment spectroscopy (DEAS). The dominant decay channel of the transient molecular negative ions consists of elimination of Br with resonances in the low electron energy region. Formation of long-lived parent anions with autodetachment lifetime = 310 μs is observed at thermal electron energies.

Multistate Multiconfiguration Quantum Chemical Computation of the Two-Photon Absorption Spectra of Bovine Rhodopsin.

Recently, progress in IR sources has led to the discovery that humans can detect infrared (IR) light. This is hypothesized to be due to the two-photon absorption (TPA) events promoting the retina dim-light rod photoreceptor rhodopsin to the same excited state populated via one-photon absorption (OPA). Here, we combine quantum mechanics/molecular mechanics and extended multiconfiguration quasi-degenerate perturbation theory calculations to simulate the TPA spectrum of bovine rhodopsin (Rh) as a model for the human photoreceptor.

Chlorination-Promoted Skeletal Transformations of Fullerenes.

Classical fullerenes are built of pentagonal and hexagonal rings, and the conventional syntheses produce only those isomers that obey the isolated-pentagon rule (IPR), where all pentagonal rings are separated from each other by hexagonal rings. Upon exohedral derivatization, the IPR fullerene cages normally retain their connectivity pattern. However, it has been discovered that high-temperature chlorination of fullerenes with SbCl or VCl can induce skeletal transformations that alter the carbon cage topology, as directly evidenced by single crystal X-ray diffraction studies of the chlorinated products of a series of fullerenes in the broad range of C to C.

Time-Resolved Photochemistry of Stiffened Stilbenes.

Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/ Z mixtures of bis(benzocyclobutylidene) (t4, c4) and ( E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S, all evolve to perpendicular molecular conformation P, followed by decay to S, while the spectra and the kinetic behavior crucially depend on the size of the stiffening ring. In 4, contrary to all previously studied stilbenes, the trans and cis absorption and excited-state spectra are nearly indistinguishable, while the corresponding isomerization times are comparable: τ = 166 ps for t4 and τ = 64 ps for c4 in n-hexane, as opposed to 114 and 45 ps in acetonitrile, respectively.

Electronic Communication between S=1/2 Spins in Negatively-charged Double-caged Fullerene C Derivative Bonded by Two Single Bonds and Pyrrolizidine Bridge.

Radical anion salt {cryptand[2.2.2] (K )} (bispheroid) ⋅3.

Rebuilding C: Chlorination-Promoted Transformations of the Buckminsterfullerene into Pentagon-Fused C Derivatives.

In recent years, many higher fullerenes that obey the isolated pentagon rule (IPR) were found capable of rearranging into molecules with adjacent pentagons and even with heptagons via chlorination-promoted skeletal transformations. However, the key fullerene, buckminsterfullerene I -C, long seemed insusceptible to such rearrangements. Now we demonstrate that buckminsterfullerene yet can be transformed by chlorination with SbCl at 420-440 °C and report X-ray structures for the thus-obtained library of non-IPR derivatives.

Facile Separation, Spectroscopic Identification, and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene.

We survey the structure and electronic properties of the family of higher trifluoromethylated C (CF ) molecules with n=14, 16, 18, and 20. Twenty-two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π-system topologies, which enabled us to study the interplay between the CF addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends.

Experimental and Theoretical Approach to Variable Chlorination-Promoted Skeletal Transformations in Fullerenes: The Case of C.

The first example of three alternative chlorination-promoted skeletal transformation pathways in the same fullerene cage is presented. Isolated-pentagon-rule (IPR) C(19) undergoes both Stone-Wales rotations to give non-IPR CCl and C losses to form nonclassical C and non-IPR C. X-ray structural characterization of the transformation products and a theoretical study of their formation pathways are reported.

Tuning Stilbene Photochemistry by Fluorination: State Reordering Leads to Sudden Polarization near the Franck-Condon Region.

Spontaneous polarization of a nonpolar molecule upon photoexcitation (the sudden polarization effect) earlier discussed for 90°-twisted alkenes is observed and calculated for planar ring-fluorinated stilbenes, trans-2,3,5,6,2',3',5',6'-octofluorostilbene (tF2356) and trans-2,3,4,5,6,2',3',4',5',6'-decafluorostilbene (tF23456). Due to the fluorination, Franck-Condon states S and S are dominated by the quasi-degenerate HOMO-1 → LUMO and HOMO-2 → LUMO excitations, while their interaction gives rise to a symmetry-broken zwitterionic S state. After optical excitation of tF2356, one observes an ultrafast (∼0.

Effect of a Tertiary Butyl Group on Polar Solvation Dynamics in Aqueous Solution: Femtosecond Fluorescence Spectroscopy.

We monitor the time-dependent Stokes shift (TDSS) of fluorescence from the zwitterionic probe N-methyl-6-oxyquinolinium betaine in water. A spectral relaxation time τ = 0.57 ps (at 20.

Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells.

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair.