M. C. Ruiz Delgado

Vibrational study of push–pull chromophores for second-order non-linear optics derived from rigidified thiophene π-conjugating spacers

Abstract The solid-state infrared absorption and Raman scattering spectra of 5-(2,2-dicyanoethenyl)-5′-[(E)- N , N ′-dimethylaminobenzylidene)methyl] bithiophene which can be viewed as a π-conjugated bridge (bithiophene) substituted with an electron-donor group ((E)- N , N ′-dimethylaminobenzylidene)methyl), and with an electron-acceptor group (2,2-dicyanoethenyl), are reported. The main infrared and Raman features have been analyzed and assigned to precise normal modes with the help of accurate Density Functional Theory calculations. Vibrational bands associated with the donor, with the acceptor and with the oligothienyl bridge have been identified. The peak position of the IR-active stretching vibration associated with the dicyano groups has been related to the degree of charge transfer from the donor to the acceptor in the molecule. The great ressemblance between the infrared and Raman spectra reveals that this molecule behaves as an effective push–pull system. Theory full accounts for the vibrational properties of this type of push–pull system in relationship with its electronic structure.

Efficiency of the π conjugation in a novel family of α,α′-bisphenyl end-capped oligothiophenes by means of Raman spectroscopy

The degree of π conjugation in a novel series of molecular materials containing a central oligothiophene moiety of variable length, with its end α positions capped by phenyl groups (PnTP; n=1–4) is closely inspected by means of Fourier-transform infrared and Fourier-transform Raman spectroscopies in the neutral state as solids. Density functional theory quantum chemical calculations were performed for each co-oligomer, at the B3LYP/6-31G** level, to obtain the optimized molecular geometry and force field. The thermal stability of these oligothiophenes has been also investigated, at the molecular level, by recording infrared and Raman spectra at different temperatures between −170 °C and 160 °C.

Infrared and Raman features of a series of α,ω-bis(arylthio)oligothiophenes as molecular wires. A π-electron delocalization efficiency study

Fourier transform infrared and Raman spectra of a novel series of neutral α,ω-bis(mesitylthio)oligothiophenes and some α,ω-bis(mesitylthio)oligothiophenes containing ethylenedioxy groups at the β positions, with various chain lengths have been investigated. Because these compounds contain carbon-sulfur linkages they can be viewed as models for prototypical surface-bound molecular wires in which the oligomer is linked to the surface by a thiol-metal bond. Thus, interactions between the conjugated moiety and the metallic surface or cluster can be simulated. These studies are very important in order to apply molecular systems in micro and optoelectronic devices. The statements of effective conjugation coordinate theory and density functional theory calculations let us describe the specific electronic interactions between the mesitylthio groups and the oligothiophene backbone. An increased π-electron delocalization or conjugation length with respect to the α,ω-bis(alkyl)oligothiophenes of the same length has ...

UV - Vis, IR, Raman and theoretical characterization of a novel quinoid oligothiophene molecular material

A quinoid-type oligothiophene, 3 0 ,4 0 -dibutyl-5,5 00 -bis(dicyanomethylene)-5,5 00 -dihidro-2,2 0 :5 0 ,2 00 -terthiophene, which can be viewed as an analog of TCNQ, has been investigated by spectroelectrochemistry and density functional theory calculations, in its neutral and dianionic states. Electrochemical data show that the molecule can be both reduced and oxidized at relatively low potentials. Upon reduction, both experiments and theory agree well with the generation of a dianionic charged species. The model shows that the electronic structure of the dianion is consistent with two anionic dicyanomethylene groups attached to a central terthienyl spine having an aromatic structure. The two negatively charged dicyanomethylene groups conjugate with the terthiophene allowing for the extension of the p-delocalized system over the whole molecule. The stability of the dianionic species, due to its aromatic character, gives support to the low value for the electrochemical two-electron reduction process. Infrared spectra of the neutral and of the dianion species have been assigned and correlated. q 2003 Elsevier Science B.V. All rights reserved.

Solution-processed N-trialkylated triindoles for organic field effect transistors

Three crystalline N-trialkyltriindoles in which the length of the alkyl chains attached to the nitrogen has been enlarged from a methyl to a butyl and to a hexyl group have been investigated in the search for semiconducting triindole easy to process from solution. We have found that the number of carbon atoms of the N-alkyl chains has a significant impact on how these molecules interact with each other in the bulk materials and it strongly influences the final morphology of the crystals, which grow as long crystalline wires, cubes or microbelts. Single crystal analysis allows us to recognize the contribution of several cooperative CH–π interactions to guide the self-assembly of these types of molecules. In addition, alkyl chain engineering allows triindole derivatives processable for solution, which render OFETs showing field effect mobilities of 0.03 cm2 V−1 s−1 and 6 × 10−3 cm2 V−1 s−1 when vapor deposited and drop casted, respectively. The results of this study represent a step forward towards the rational control of the supramolecular arrangement of this high performance semiconducting platform, this being a key fact for designing efficient solution-processed organic semiconductors.

A combined MD/QM and experimental exploration of conformational richness in branched oligothiophenes

Infrared (IR) absorption and vibrational Raman spectra of a family of branched oligothiophenes have been determined experimentally as well as theoretically. The molecular spectra have been compared to those of the linear analogues, with identification made of spectral features due to structural properties that are valued in organic solar cell applications. The theoretical spectra have been obtained through a newly developed method in which individual conformer spectra, calculated at the time-dependent DFT level in this work, are weighted by statistics extracted from classical molecular dynamics trajectories. The agreement with experiment for the resulting averaged spectra is at least as good as, and often better than, what is observed for Boltzmann-weighted spectra. As the weights are available before the costly step of spectrum calculation, the method has the additional advantage of enabling efficient approximations. For simulating the molecular dynamics of the studied α,β-linked thiophenes and 2-methylthiophenes, high quality parameters have been derived for the CHARMM force field. Furthermore, the temperature dependence of the IR and Raman spectra has been investigated, both experimentally and theoretically.