Jean-Paul Gisselbrecht

End-cap stabilized oligoynes: model compounds for the linear sp carbon allotrope carbyne.

Three series of differently 3,5-disubstituted alpha,omega-diphenylpolyynes Ar-(C[triple bond]C)n-Ar (n=2, 4, 6, 8, 10) were synthesized under optimized Cadiot-Chodkiewicz conditions, isolated and completely characterized. These compounds can be considered as model substances for the hypothetical one-dimensional carbon allotrope carbyne Cx. The longest sp-carbon chain contains 20 atoms and is therefore the longest, purely organic polyyne studied with NMR techniques. Extinction coefficients over 600,000 M(-1) cm(-1) represent the highest measured quantitative values for that compound class so far. Comparisons with previous investigations and electrochemical studies allow the assignment of absorption for both wavelength regions structuring the UV/Vis spectra. Based on the trends in the spectroscopic behaviour of those molecules with increasing chain length, electronic as well as the NMR properties of carbyne are predicted, in line with our previously reported results. The observed stability properties promise the synthesis of even longer polyynes.

A new class of organic donor-acceptor molecules with large third-order optical nonlinearities

Donor-acceptor molecules with 4-(dimethylamino)phenyl donor and 1,1,4,4-tetracyanobuta-1,3-diene acceptor moieties are readily prepared by short, high-yielding routes. The quite small chromophores are characterised by X-ray crystallography and feature intense intramolecular charge-transfer bands, substantial quinoid character in the donor rings, reversible electrochemical reductions and oxidations and powerful third-order optical nonlinearities.

Organic super-acceptors with efficient intramolecular charge-transfer interactions by [2+2] cycloadditions of TCNE, TCNQ, and F4-TCNQ to donor-substituted cyanoalkynes.

Rivaling the best one: Thermal [2+2] cycloadditions of TCNE, TCNQ, and F(4)-TCNQ to N,N-dimethylanilino-substituted cyanoalkynes afforded a new class of organic super-acceptors featuring efficient intramolecular charge-transfer interactions. These acceptors rival the acceptor F(4)-TCNQ in the propensity for reversible electron uptake as well as in electron affinity (see figure), which makes them interesting as p-type dopants for potential application in optoelectronic devices.Thermal [2+2] cycloadditions of tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)-TCNQ) to N,N-dimethylanilino-substituted (DMA-substituted) alkynes bearing either nitrile, dicyanovinyl (DCV; -CH==C(CN)(2)), or tricyanovinyl (TCV; -C(CN)==C(CN)(2)) functionalities, followed by retro-electrocyclization, afforded a new class of stable organic super-acceptors. Despite the nonplanarity of these acceptors, as revealed by X-ray crystallographic analysis and theoretical calculations, efficient intramolecular charge-transfer (CT) interactions between the DMA donors and the CN-containing acceptor moieties are established. The corresponding CT bands appear strongly bathochromically shifted with maxima up to 1120 nm (1.11 eV) accompanied by an end-absorption in the near infrared around 1600 nm (0.78 eV) for F(4)-TCNQ adducts. Electronic absorption spectra of selected acceptors were nicely reproduced by applying the spectroscopy oriented configuration interaction (SORCI) procedure. The electrochemical investigations of these acceptors by cyclic voltammetry (CV) and rotating disc voltammetry (RDV) in CH(2)Cl(2) identified their remarkable propensity for reversible electron uptake rivaling the benchmark compounds TCNQ (E(red,1)=-0.25 V in CH(2)Cl(2) vs. Fc(+)/Fc) and F(4)-TCNQ (E(red,1)=+0.16 V in CH(2)Cl(2) vs. Fc(+)/Fc). Furthermore, the electron-accepting power of these new compounds expressed as adiabatic electron affinity (EA) has been estimated by theoretical calculations and compared to the reference acceptor F(4)-TCNQ, which is used as a p-type dopant in the fabrication of organic light-emitting diodes (OLEDs) and solar cells. A good linear correlation exists between the calculated EAs and the first reduction potentials E(red,1). Despite the substitution with strong DMA donors, the predicted EAs reach the value calculated for F(4)-TCNQ (4.96 eV) in many cases, which makes the new acceptors interesting for potential applications as dopants in organic optoelectronic devices. The first example of a charge-transfer salt between the DMA-substituted TCNQ adduct (E(red,1)=-0.27 V vs. Fc(+)/Fc) and the strong electron donor decamethylferrocene ([FeCp*(2)]; Cp*=pentamethylcyclopentadienide; E(ox,1)=-0.59 V vs. Fc(+)/Fc) is described. Interestingly, the X-ray crystal structure showed that in the solid state the TCNQ moiety in the acceptor underwent reductive sigma-dimerization upon reaction with the donor.

Dendritic Iron Porphyrins with Tethered Axial Ligands: New Model Compounds for Cytochromes.

The quantitative evaluation of the effect of an insulating dendritic shell on the redox properties of an embedded iron porphyrin core has been achieved for the first time using water-soluble dendritic iron porphyrins with tethered axial ligands (shown schematically). Thus, these complexes, whose redox properties have been determined by chemical and electrochemical methods in solvents of different polarity (CH(2)Cl(2), MeCN, H(2)O), are valid mimics for cytochromes.

Origin of intense intramolecular charge-transfer interactions in nonplanar push-pull chromophores.

Planar push–pull chromophores featuring intense intramolecular charge-transfer (CT) interactions have been extensively studied in view of their potential applications in molecular electronics and optoelectronics. In contrast, only a limited number of nonplanar low-molecular-weight donor– acceptor chromophores has been reported and the impact of nonplanarity on their p-conjugative and optoelectronic properties not been systematically investigated. Nonplanar CT chromophores tend to feature some desirable physical properties compared to their planar counterparts: they are usually more soluble, less aggregating, and more readily sublimable, forming amorphous, rather than crystalline films for potential use in optoelectronic devices. We showed recently that donor-substituted alkynes undergo a formal [2+ 2] cycloaddition with electron-accepting olefins, such as tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethanes (TCNQs), as well as dicyanovinyl (DCV) and tricyanovinyl derivatives, followed by retroelectrocyclization, under formation of nonplanar push–pull chromophores featuring intense intramolecular CT and high third-order optical nonlinearities. Nonplanar, N,N-dimethylanilino (DMA) donor-substituted 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs), obtained by [2+ 2] cycloaddition of TCNE, produce high-optical quality amorphous films by vapor-phase deposition which in the meanwhile have found first application in silicon-organic-hybrid (SOH) waveguides. A key question raised was the origin of the intense intramolecular CT interactions in these push–pull chromophores, in view of their pronounced nonplanarity which is expected to lead to disruption of donor–acceptor p-conjugation and concomitant reduction in CT efficiency and optical nonlinearity. To investigate the effects of sterically enforced deconjugation on optoelectronic properties, we prepared two new series of push–pull chromophores (1 and 2, and 3–8), by adding TCNE or TCNQ to tetrathiafulvalene (TTF)or ferrocenyl (Fc)-substituted alkynes, respectively. These strong electron donors have found numerous applications in intermolecular and intramolecular CT systems, but have not seen much use for activating alkynes electronically for the cycloaddition of TCNE or TCNQ. TTF-appended TCBD 1 was obtained in 41 % yield as a deep blue solid by reaction of TCNE with TTF-substituted alkyne 9 in 1,2-dichloroethane at 80 8C (Scheme 1). The electronically more activated alkyne 10, with both TTF and DMA donor groups, reacted at room temperature to give 2 in 79 % yield. The ferrocene-substituted expanded TCNQs 3–8 were formed as black metallic-like solids in 41–81 % yield by regioselective cycloaddition between TCNQ and the acetylenic precursors 11–16. With the exception of 3 and 8, these push–pull chromophores are thermally stable up to 300 8C, as revealed by thermal gravimetric analysis (TGA); compound 6 can actually be sublimed without decomposition at about 250 8C/1 10 6 Torr. Single crystals of 1 and 3–5 suitable for X-ray analysis were grown from CH2Cl2/hexane at 15 8C (Figure 1 and Figure S1–S4 in the Supporting Information). Considerable nonplanarity is observed in the TCBD and expanded TCNQ acceptor moieties. Thus, the dihedral angle q (C1-C2-C17C18) between the two DCV planes in 1 (with two independent molecules) is 92.7(2)8. In the expanded TCNQ chromophores 3–5, the dihedral angle q between the DCV and the cyclohexa-2,5-diene-1,4-diylidene moiety changes from 51.9(4)8 (3, torsional angle C1-C2-C3-C4, Figure S2) to 68.6(2)8 (5, C5-C8-C9-C16, Figure S4), and to 94.0(2)8 (4, C1-C12-C13-C14). Sterically enforced p-deconjugation is [a] Dr. S.-i. Kato, Dr. M. Kivala, Dr. W. B. Schweizer, Prof. Dr. F. Diederich Laboratorium f r Organische Chemie, ETH Z rich Hçnggerberg, HCI, 8093 Z rich (Switzerland) Fax: (+41) 44-632-1109 E-mail : diederich@org.chem.ethz.ch [b] Prof. Dr. C. Boudon, Dr. J.-P. Gisselbrecht Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide Intstitut de Chimie-UMR 7177, C.N.R.S. Universit de Strasbourg 4, rue Blaise Pascal, 67000 Strasbourg (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200901630.

Property Tuning in Charge‐Transfer Chromophores by Systematic Modulation of the Spacer between Donor and Acceptor

A series of donor-acceptor chromophores was prepared in which the spacer separating 4-dimethylanilino (DMA) donor and C(CN)(2) acceptor moieties is systematically varied. All of the new push-pull systems, except 4 b, are thermally stable molecules. In series a, the DMA rings are directly attached to the central spacer, whereas in series b additional acetylene moieties are inserted. X-ray crystal structures were obtained for seven of the new, intensely colored target compounds. In series a, the DMA rings are sterically forced out of the mean plane of the residual pi system, whereas the entire conjugated pi system in series b is nearly planar. Support for strong donor-acceptor interactions was obtained through evaluation of the quinoid character of the DMA ring and by NMR and IR spectroscopy. The UV/Vis spectra feature bathochromically shifted, intense charge-transfer bands, with the lowest energy transitions and the smallest optical gap being measured for the two-dimensionally extended chromophores 6 a and 6 b. The redox behavior of the push-pull molecules was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In the series 1 b, 2 b, 4 b, 5 b, in which the spacer between donor and acceptor moieties is systematically enlarged, the electrochemical gap decreases steadily from 1.94 V (1 b) to 1.53 V (5 b). This decrease is shown to be a consequence of a reduction in the D-A conjugation with increasing spacer length. Degenerate four-wave mixing experiments reveal high third-order optical nonlinearities, pointing to potentially interesting applications of some of the new chromophores in optoelectronic devices.

Photoinduced processes in fullerenopyrrolidine and fullerenopyrazoline derivatives substituted with an oligophenylenevinylene moietyElectronic supplementary information (ESI) available: synthetic procedures and full characterization of all new compounds. See http://www.rsc.org/suppdata/jm/b2/b200432a/

Fullerene derivatives A-3PV and B-3PV in which an oligophenylenevinylene trimeric subunit (3PV) is attached to C60 through, respectively, a pyrrolidine or a pyrazoline ring have been prepared. The electrochemical and excited-state properties of the multicomponent arrays A-3PV and B-3PV have been investigated in solution using the related oligophenylenevinylene derivative 3PV, fullerenopyrrolidine A and fullerenopyrazoline B as reference compounds. In A-3PV quantitative OPV → C60 photoinduced singlet–singlet energy transfer has been observed. Population of the lowest fullerene singlet excited state is followed by nearly quantitative intersystem crossing to the lowest fullerene triplet excited state in CH2Cl2 and toluene, whereas OPV → C60 electron transfer is able to compete significantly in the more polar solvent benzonitrile. In the case of B-3PV, the excited-state properties are more complex due to the electron donating ability of the pyrazoline ring. As observed for A-3PV, quantitative OPV → C60 photoinduced singlet–singlet energy transfer occurs in B-3PV. However, in this case, the population of the lowest fullerene singlet excited state is followed by an efficient electron transfer from the pyrazoline ring in CH2Cl2 and benzonitrile. In B-3PV, studies of the dependence of photoinduced processes on solvent polarity, addition of acid, and temperature also reveal that this compound can be considered as a fullerene-based molecular switch, the switchable parameters being the photoinduced processes. Finally, A-3PV and B-3PV have been tested as active materials in photovoltaic devices and the differences of light to energy conversion efficiencies found for the two compounds have been rationalised on the basis of their photophysical properties.

A Copper(I) Bis‐phenanthroline Complex Buried in Fullerene‐Functionalized Dendritic Black Boxes

Virtual inaccessibility to external contact was revealed by electrochemical investigations for a bis(1,10-phenanthroline)copper(I) core embedded in dendrimers with up to 16 peripheral fullerene units (shown schematically). With increasing numbers of fullerene units, less and less light is available to the core, and the small quantity of light energy that reaches the central Cu(I) complex is returned to the external fullerenes by energy transfer-the central core is buried in a dendritic black box.

Dramatically Enhanced Fluorescence of Heteroaromatic Chromophores upon Insertion as Spacers into Oligo(triacetylene)s

In continuation of a previous study on the modulation of π-electron conjugation of oligo(triacetylene)s by insertion of central hetero-spacer fragments between two (E)-hex-3-ene-1,5-diyne ((E)-1,2-diethynylethene, DEE) moieties (Fig. 1), a new series of trimeric hybrid oligomers (14–18 and 22–24, Fig. 2) were prepared (Schemes 1–3). Spacers used were both electron-deficient (quinoxaline-based heterocycles, pyridazine) and electron-rich (2,2′-bithiophene, 9,9-dioctyl-9H-fluorene) chromophores. With 19–21 (Scheme 4), a series of transition metal complexes was synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramolecular assembly. The UV/VIS spectra (Fig. 3) revealed that the majority of spacers provided hetero-trimers featuring extended π-electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer 13 and homo-trimer 12 (Fig. 5). This increase in emission intensity appears as a general feature of these systems: even if the spacer molecule is non-fluorescent, the corresponding hetero-trimer may show a strong emission (Table 2). The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV) (Table 3 and Fig. 5). In each case, the first one-electron reduction step in the hetero-trimers appeared anodically shifted compared with DEE dimer 13 and homo-trimer 12. With larger spacer chromophore extending into two dimensions (as in 14–18, Fig. 2), the anodic shift (by 240–490 mV, Table 3) seems to originate from inductive effects of the two strongly electron-accepting DEE substituents rather than from extended π-electron conjugation along the oligomeric backbone, as had previously been observed for DEE-substituted porphyrins.

Electrospray mass spectrometry of electrochemically ionized molecules : Application to the study of fullerenes

Abstract We describe the characterization, by Electrospray Ionization Mass Spectrometry (ESI-MS), of neutral species using their redox properties. These molecules were ionized by oxidation-reduction reactions either off-line, in a classical electrochemical cell, or on-line using the fact that the ES source behaves like an electrolysis cell. This study has been performed both oxidation (positive ions) and reduction (negative ions) reactions. Limitations as to the ability of compounds to be analyzed on-line have been examined as have limitations of off-line reduction in the case of fullerenes. This study offers a new approach for the ESI-MS analysis of compounds difficult to ionize.