Maurice Gross

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.

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.

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.

LEXICON-GRAMMAR AND THE SYNTACTIC ANALYSIS OF FRENCH

A lexicon-grammar is constituted of the elementary sentences of a language. Instead of considering words as basic syntactic units to which grammatical information is attached, we use simple sentences (subject-verb-objects) as dictionary entries. Hence, a full dictionary item is a simple sentence with a description of the corresponding distributional and transformational properties.The systematic study of French has led to an organization of its lexicon-grammar based on three main components:- the lexicon-grammar of free sentences, that is, of sentences whose verb imposes selectional restrictions on its subject and complements (e.g. to fall, to eat, to watch),- the lexicon-grammar of frozen or idiomatic expressions (e.g. N takes N into account, N raises a question,- the lexicon-grammar of support verbs. These verbs do not have the common selectional restrictions, but more complex dependencies between subject and complement (e.g. to have, to make in N has an impact on N, N makes a certain impression on N)These three components interact in specific ways. We present the structure of the lexicon-grammar built for French and we discuss its algorithmic implications for parsing.The construction of a lexicon-grammar of French has led to an accumulation of linguistic information that should significantly bear on the procedures of automatic analysis of natural languages. We shall present the structure of a lexicon-grammar built for French and will discuss its algorithmic main implications.

Lexicon-grammar: the representation of compound words

The essenti~d feature of a lexicon-grammar is that the elementary unit of computation and storage is the simple sentence: snbleet-verb-complement(s). -this type of representation is obviously needed for verbs: limiting a verb to its shape has no meaning other than typographic, ~ir]ce a verb cannot be separated from its subject and essential coreplemenl(s) 2. We have shown (M, Gross 1975) that given a verb, Or equivalent ly a simple sentence, the set of syntactic propert ies that describes its variations is unique: in general, no ether verb has an identical syntactic paradigm 3. As a consequence, the propert ies of each verbal construction must be represented in a texicon--grammar. The lexicon has no significance taken as an isolated component and the gr~rnmar tempera:at, viewed as independent of the lexicon, will have to be l imi ted to cer ta in complex sentences,

Redox properties of porphycenes and metalloporphycenes. A comparison with porphyrins

An electrochemical analysis of a series of porphycenes and metalloporphycenes in tetrahydrofuran, N,N-dimethylformamide, and dichloromethane is reported. This analysis combined the use of polarographic, steady-state voltammetric, cyclic voltammetric, and spectroelectrochemical methods. The free-base porphycenes studied were porphycene (H 2 Pc), 2,3,6,7,12,13,16,17-octaethylporphycene (H 2 OEPc), 2,7,12,17-tetra-n-propylporphycene (H 2 TPrPc), and its tetrabromo derivative, respectively

A supramolecular cup-and-ball C60-porphyrin conjugate system

In addition to the ammonium-crown ether recognition, pi-stacking interactions between the C60 sphere and the porphyrin moiety have been evidenced in a supramolecular complex obtained from a porphyrin-crown ether conjugate and a fullerene derivative bearing an ammonium unit.