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A series of donor–acceptor–acceptor (D–A–A) and donor–acceptor–donor (D–A–D) systems based on a pyrimidine π-spacer with various substituents at the C-2 position has been successfully prepared. The synthesis involved site-selective palladium cross-coupling reactions of chloropyrimidines with triorganoindium reagents and proceed in good yields and with atom economy. 4-(N,N-Diphenylamino)phenyl was chosen as the donor group and thien-2-yl dicyanovinylene as the acceptor one. The optical, vibrational, electrochemical, and density functional theory (DFT) calculations of these molecular systems were analyzed, and experimental values show the important role of the substituents at the C-2 position of the pyrimidine with stronger electron accepting ability, absorption in a wide range of UV/vis, acceptable fluorescence lifetime, and effective intramolecular charge transfer (ICT) properties. The ICT was observed in both series by the bathochromic shift on increasing the polarity of the solvent. In addition, DFT calculations found lower lowest unoccupied molecular orbitals of D–A–A molecules that suggest good electron ejection and transportation, being good properties for their application in various organic optoelectronic devices.

In this paper, experimental and computational investigations are combined to analyze the impact of the diradical character in the photonic and chemical properties of two tetracyano quinodimethane derivatives of phenylene-vinylenes. The photonic properties are evaluated with high-level quantum-chemical calculations and are rationalized in the context of the four-level model typical of diradical molecules, including one triplet and three singlet states, whereas the diradical extent in the ground electronic state is shown to be the driving force for the dimerization reactions. To this end DFT, CASSCF, and CASPT2//CASSCF calculations are carried out and complemented with experimental UV–vis–NIR absorption and emission measurements, as a function of the temperature along with resonance Raman spectroscopy investigations. The study of diradical molecules with enhanced chemical stability in the framework of organic electronics is an important field of research in organic π-conjugated molecules with direct applications in organic electronics.

Three new hexaazatriphenylene (HAT)-based electron-accepting molecules with octupolar disc-like symmetry that combine the HAT core with six branches of electron-donor thiophenes in two modalities have been synthesized: (i) with six donor thiophenes and bithiophenes delineating a six-donor-to-one-acceptor (6–1) profile and (ii) with six donor–acceptor branches configuring a 6–6–1 acceptor–donor–acceptor triad. The 6-fold accumulation of donors and acceptors in the periphery of the HAT core is expected to tune the molecular electronic and optical properties. An exhaustive analysis of these properties as a function of the 6–1 and 6–6–1 stoichiometry of the molecules is described by combining a palette of experimental spectroscopic techniques such as electronic absorption (from the ground electronic and excited states), emission (fluorescence and phosphorescence), ultraviolet photoelectron spectroscopy, spectroelectrochemistry, and vibrational Raman have been implemented, all combined with electrochemistry and molecular theoretical modeling. A particular focus on the charged species and the charge distribution around the 6–1 and 6–6–1 patterns is conducted. Structure–property relationships have been outlined. The complete understanding of all these properties might help to design improved chromophores based on the HAT structure and to anticipate new properties.

The relationships between the chiroptical activity and the vibrational normal modes of epichlorohydrin have been investigated on the basis of a nonredundant internal coordinate definition not reported until now. These coordinates were verified by comparing, for the lower energy conformers, the diagonal quadratic force constants and were found to display similar values among conformers and to be consistent with the molecular structure of epichlorohydrin and its vibrational circular dichroism (VCD) spectrum. Boltzmann population factors were used to calculate the weighted sum of the individual VCD and IR spectra of the three lower energy conformers, which accurately fitted the experimental spectra of (R)-epichlorohydrin. The electric and magnetic transition dipole moments of the 24 vibrational normal modes were calculated for the most stable conformers. The combined analysis of these vectors and the normal mode description, given in terms of the potential energy distribution, allowed us to investigate the role of the functional groups (methylene, chlorine) and the type of internal coordinates (stretching, bending, etc.) in the chiroptical activity of the vibrations.

Here we present the synthesis and optical and structural characterization of a new series of alternating donor–acceptor copolymers based on 3,4-ethylenedioxythiophene (EDOT). The donor consists of phenylene, alkylated fluorene, or diethynyl-1,4-phenylene as the aryl units copolymerized with the EDOT group with and without a 9,10-anthraquinone (AQ) side chain as the acceptor group, namely, as PEX-AQand PEX, respectively. The changes in the electronic absorption/emission spectra and redox properties are analyzed in detail as a function of (i) the composition of the copolymers and (ii) the inclusion of the pendant 9,10-anthraquinone. Density functional theory calculations are used to interpret the experimental results. Special emphasis is placed on the flexibility of the phenylene-based copolymer spine which favors the tendency toward aggregation and confers interesting solvathocromic, thermochromic, and sonochromic properties when applying external stimuli. This is explained by means of an order–disorder conformational transformation (driven by π–π stacking) in solution upon ultrasonication, temperature changes, and the nature of the solvents. A comparison of the transient triplet–triplet absorption spectra of the phenylene-based PEBcopolymer in the unaggregated and aggregated forms reveals the formation of accessible triplet excited states whose nature is discussed in connection with the molecular flexibility of the copolymer backbone. These studies highlight the relevance of the precise control of the polymer architecture (donor–acceptor strategy in PEXversus double-cable concept in PEX-AQ) for suitable tunability of the optical and electronic properties of processable conjugated polymers for organic electronics.

The electronic and photophysical properties of 6,11-dihydro-5H-diindolo[2,3-a:2′,3′-c]carbazole, an asymmetric cyclic dehydrotrimer of indole, have been explored and compared to its symmetric analogue, 10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (triindole), a well-known high hole mobility semiconductor. To this purpose, we use a joint experimental and theoretical approach that combines absorption and emission spectroscopies, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Lowering the symmetry of the triindole platform causes a red-shift of the absorption edge and emission maxima and improved the fluorescence quantum yield. Cyclic voltammetry and spectroelectrochemistry reveal the reversible nature of the two observable oxidation processes in the alkylated asymmetric triindoles together with an increase in the stabillity of their oxidized species. On the other hand, the insertion of alkyl groups on the nitrogen atoms results in a further fluorescence enhancement although larger reorganization energies are found. DFT and time-dependent (TD-DFT) calculations successfully support the experimental data and aid in the understanding of the tuning of the physicochemical properties of the triindole platform upon symmetry lowering toward their incorporation in electronic devices.

By changing the position of the homochiral alkoxy substituents of C3‐symmetric 1,3,5‐trialkynylbenzenes from the center to the periphery, the macroscopic chirality of the resulting aggregates (crystals or fibers), studied by various spectroscopic and microscopic techniques, was inverted, as confirmed by single‐crystal X‐ray diffraction analysis.

First-principles quantum chemical approach has been used to understand the origin of the chiro-optical signal induced by the chiral aggregation of an achiral chromophore. The study was focused in predicting the circular dichroism (CD) spectra of different π-stacked columnar oligomers built with C3star-shape molecular bricks. We studied the influence of the relevant structural self-assembly parameters on the CD spectra (i.e., the number of units, the rotation angle and the intermonomer distance). A detailed analysis was based on the MO topologies and the magnetic and electric transition dipole moments, the vectors which determine the CD intensities, has been conducted. We have rationalized the influence of the various structural factors of supramolecular self-assemblies in connection with the nature of their CD spectroscopic signal, which provides new avenues for structure–spectroscopic relationships.

A new hexaazatriphenylene (HAT) derivative formed by the fusion of three HAT units has been prepared and its electronic and molecular structures have been fully characterized by optical and vibrational Raman spectroscopy, electrochemistry, solid‐state UV and inverse photoemission spectroscopy (UPS and IPES), and by quantum‐chemical calculations. A comparative HAT versus tri‐HAT study was performed. The fusion of three HAT molecules causes modifications in the optical and electrochemical properties consistent with enhanced π‐electron delocalization attained in a bigger planar core. Such combined experimental and theoretical studies are useful to balance chemical design with supramolecular engineering directed to find enhanced characteristics for new organic semiconductor applications.

A series of enantiopure, monodisperse alleno‐acetylenic cyclooligomers were synthesized. The single‐crystal X‐ray structures of the cyclic trimer and hexamer were resolved, providing insights into the symmetry of these molecules. Electronic circular dichroism (ECD), optical rotatory dispersion (ORD), Raman spectroscopy, and vibrational circular dichroism (VCD) data were analyzed with the aid of theoretical calculations. This multidimensional approach ultimately provided general guidelines that are useful for designing carbon‐rich compounds with intense chiroptical properties.

We have prepared a new series of mixed thiophene–pyrrole oligomers to investigate the electronic benefits arising from the combination of these two heterocycles. The oligomers are functionalized with several hexyl and aryl groups to improve both processability and chemical robustness. An analysis of their spectroscopic (absorption and emission), photophysical, electrochemical, solid state, and vibrational properties is performed in combination with quantum‐chemical calculations. This analysis provides relevant information regarding the use of these materials as organic semiconductors. The balance between the high aromatic character of pyrrole and the moderate aromaticity of thiophene allows us to address the impact of the coupling of these heterocycles in conjugated systems. The data are interpreted on the basis of the aromaticity, molecular conformations, ground and excited electronic state structures, frontier orbital topologies and energies, oxidative states, and quinoidal versus aromatic competition.

This work presents an analysis of the structural, electrochemical, and optical properties of a family of triisopropylsilyl end‐capped oligothienoacenes (TIPS‐Tn‐TIPS, n=4–8) by combining cyclic voltammetry, spectroscopic techniques, and quantum‐chemical calculations. TIPS‐Tn‐TIPS compounds form stable radical cations, and dications are only obtained for the longest oligomers (n=7 and 8). Oxidation leads to the quinoidization of the conjugated backbone, from which electrons are mainly extracted. The absorption and fluorescence spectra show partially resolved vibronic structures even at room temperature, due to the rigid molecular geometry. Two well‐resolved vibronic progressions are observed at low temperatures due to the vibronic coupling, with normal modes showing wavenumbers of ≈1525 and ≈480 cm−1. Optical absorption bands display remarkable bathochromic dispersion with the oligomer length, indicative of the extent of π conjugation. The optical properties of the oxidized compounds are characterized by in situ UV/Vis/NIR spectroelectrochemistry. The radical cation species show two intense absorption bands emerging at energies lower than in the neutral compounds. The formation of the dication is only detected for the heptamer and the octamer, and shows a new band at intermediate energies. Optical data are interpreted with the help of density functional theory calculations performed at the B3LYP/6‐31G** level, both for the neutral and the oxidized compounds.

A family of quinoidal oligothiophenes, from the dimer to the hexamer, with fused bis(butoxymethyl)cyclopentane groups has been extensively investigated by means of electronic and vibrational spectroscopy, electrochemical measurements, and density functional calculations. The latter predict that the electronic ground state always corresponds to a singlet state and that, for the longest oligomers, this state has biradical character that increases with increasing oligomer length. The shortest oligomers display closed‐shell quinoidal structures. Calculations also predict the existence of very low energy excited triplet states that can be populated at room temperature. Aromatization of the conjugated carbon backbone is the driving force that determines the increasing biradical character of the ground state and the appearance of low‐lying triplet states. UV/Vis, Raman, IR, and electrochemical experiments support the aromatic biradical structures predicted for the ground state of the longest oligomers and reveal that population of the low‐lying triplet state accounts for the magnetic activity displayed by these compounds.

A detailed investigation of the optical and electrochemical properties of two pentathienoacene derivatives, 2,6‐bis(trimethylsilyl)‐α‐pentathienoacene (TMS‐T5‐TMS) and 2,6‐bis(triisopropylsilyl)‐α‐pentathienoacene (TIPS‐T5‐TIPS), as the neutral and oxidized species was performed in the temperature range of 80–300 K. The experimental solution UV/Vis and solid‐state Raman spectra were interpreted by using time‐dependent DFT and DFT quantum chemical calculations at the B3LYP/6‐31G** level. Bond lengths, HOMO–LUMO positions, and charge distribution were also predicted by computational methods for both the neutral and oxidized states of each thienoacene. As evidenced by ESR and spectroelectrochemical data, upon oxidation the pentathienoacene derivative with the less sterically hindering trimethylsilyl solubilizing groups, TMS‐T5‐TMS, undergoes π dimerization to form [TMS‐T5‐TMS]22+. In contrast, TIPS‐T5‐TIPS, with the more bulky triisopropylsilyl solubilizing groups, was oxidized to the radical cation but dimerization was prevented due to steric interactions. These experimental observations are supported by DFT calculations, which were used to investigate [TMS‐T5‐TMS]22+and [TIPS‐T5‐TIPS]22+π dimers in the solid state and in solution. The redox potentials and absorption peak locations corresponding to the radical cations and π dimer of TMS‐T5‐TMSwere identified experimentally.

We have synthesized three new molecules that have three thienylethynyl arms substituting a central benzene core and different electron donor/acceptor groups in the three remaining phenyl positions. The absorption, fluorescence, phosphorescence, and transient triplet–triplet spectra are analyzed in the light of the electronic structure of the ground and excited states obtained from quantum‐chemical calculations. From the above, the relevant photophysical data (including quantum yields, lifetimes, and rate constants) could be derived. It was found that the major deactivation pathway is internal conversion, which competes with the fluorescence and intersystem crossing processes. For the three investigated compounds, we provide convincing theoretical support corroborating these findings and further conclusions based on the theoretical information obtained. These molecules are one of the very few cases in which the depolarization ratios, obtained from the NLO optical measurements, clearly reflect the octopolar configuration. Molecular hyperpolarizabilities have been measured and display a typical dependence on the donor–acceptor substitution pattern.

What's your role?New oligothiophene–vinylene compounds have been synthesized to study the role of the conjugated chain in two different cases (see scheme; MV=mixed valence). The electronic and molecular structures were analyzed by means of electronic, X‐ray photoelectron, and Raman spectroscopy, together with thermo spectroscopy, electrochemistry, and DFT calculations.

A series of tricyanovinyl (TCV)‐substituted oligothiophenes was synthesized and investigated with a number of physical methods including UV/Vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X‐ray diffraction, and cyclic voltammetry. Mono‐ or disubstituted oligomers were prepared by the reaction of tetracyanoethylene with mono‐ or dilithiated oligomers. The comparative effects of the symmetric and asymmetric substitutions in the electronic and molecular properties have been addressed. These oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison with unsubstituted molecules. The analysis of the electronic properties of the molecules was assisted by density functional theory calculations, which are in excellent agreement with the experimental data. TCV substitution influences the energies of the frontier orbitals, especially with respect to the stabilization of LUMO orbitals. X‐ray structural characterization of a monosubstituted oligomer exhibits π‐stacking with favorable intermolecular interactions. NLO results agree with the role of the intramolecular charge‐transfer feature in the asymmetric samples. These results furthermore exalt the role of conformational flexibility in the disubstituted compounds and reveal an unexpected nonlinear optical activity for symmetric molecules. Regarding the electronic structure, the interpretation of the vibrational data reflects the balanced interplay between aromatic and quinoid forms, finely tuned by the chain length and substitution pattern. The electronic and structural properties are consistent with the semiconducting properties exhibited by these materials in thin film transistors (TFTs).

Herein, a Raman spectroscopic study of a new family of 2,5‐di(2‐thienyl)phospholes and thienyl‐capped 1,1′‐diphospholes is presented. The Raman spectra have been carefully assigned with the help of density functional calculations. For di(2‐thienyl)phospholes, two well‐differentiated groups of Raman bands exist that arise either from the central phosphole ring or from the outer thiophene substituents. These data reveal a segmentation of the electronic structure. This paper reports interesting relationships between geometrical data such as the BLA (bond‐length alternation) parameter and Raman band wavenumbers. These correlations are unprecedented in the chemistry of phospholes and have been used to interpret the evolution of the electronic structure (aromaticity⇄π‐conjugation) upon 1) substitution of the central sulfur atom of terthiophene by phosphorus and 2) P‐functionalization. Increasing the coordination number of the phosphole ring results in intramolecular charge transfer. The best scenario for phosphole aromaticity is found for 1,1′‐diphospholes.

A series of nonlinear optical (NLO) donor–acceptor (D–A) chromophores containing a fused terthiophene, namely dithienothiophene (DTT), as the electron relay, the same donor group, and acceptors of various strengths, has been investigated by means of infrared and Raman spectroscopies, both in the solid state as well as in a variety of solvents, to evaluate the effectiveness of the intramolecular charge transfer from the electron‐donor to the electron‐acceptor end groups. The Raman spectral profiles of these NLO‐phores measured from their dilute solutions have been found to be rather similar to those of the corresponding solids, and thus their intramolecular charge transfer (ICT) shows very little dependence on the solvent polarity. The experimental results obtained for the DTT‐containing NLO‐phore with a 4‐(N,N‐dibutylamino)styryl end group as the donor and a 2,2‐dicyanoethen‐1‐yl end group as the acceptor differ from those previously obtained for two parent “push–pull” chromophores with the same D–A pair but built‐up around either a bis(3,4‐ethylenedioxythienyl) (BEDOT) or a bithienyl (BT) electron relay. Vibrational spectroscopy shows that DTTis significantly more efficient as an electron relay than BT (which has the same number of conjugated CC bonds) or BEDOT (which can be viewed as a rigidified version of BT on account of noncovalent intramolecular interactions between heteroatoms of adjacent rings). Density functional theory (DFT) calculations have also been performed on these NLO‐phores to assign their main electronic and vibrational features and to obtain information about their structures. An additional merit of these molecular materials was revealed by the infrared spectra of the DTT‐based NLO‐phores recorded at different temperatures. Thus, spectra recorded between −170 and 150 °C did not show any substantial change, indicating that the materials have a high thermal stability, which is of significance for their use as active components in optoelectronic devices.

Two types of push–pull chromophores built around thiophene‐based π‐conjugating spacers rigidified by either covalent bonds or noncovalent intramolecular interactions have been analysed by means of IR and Raman spectroscopical measurements in the solid state as well as in a variety of solvents. Comparison of the Raman features of NLO‐phores based on a covalently rigidified dithienylene (DTE) spacer with those of their open chain DTE analogues shows that the bridging of the central double bond of DTE with the nearest β‐positions of the thienyl units through two ethylene bridges significantly improves the intramolecular charge transfer. This also occurs for NLO‐phores based on a 2,2′‐bi(3,4‐ethylenedioxythiophene) (BEDOT) spacer as compared with their corresponding parent compounds based on an unsubstituted bithiophene (BT) spacer. For NLO‐phores based on a BEDOT spacer, noncovalent intramolecular interactions between sulfur and oxygen atoms are responsible for the rigidification of the spacer. The Raman spectra of these NLO‐phores obtained in the form of solutes in dilute solutions reveal two different behaviours: i) chromophores based on covalently bridged or open chain DTE spacers display Raman spectral profiles in solution quite similar to those of the corresponding solids, with a very little dependence on the polarity of the solvent, while ii) larger spectral changes are noticed for NLO‐phores built around BEDOT or BT spacers on going from solids to solutions. In the second case, spectral changes must be ascribed not solely to conformational distortions of the donor and acceptor end groups with respect to the π‐conjugated backbone mean‐square‐plane (as for the DTE‐based NLO‐phores) but also to distortions of the thienyl units of the π‐conjugating spacer from coplanarity. The insertion of vinylenic bridges between the thienyl units of the π‐conjugating spacer and between the spacer and the donor and acceptor end groups is a suitable strategy to reach a fairly large intramolecular charge transfer both in polar and nonpolar solvents. Density functional theory (DFT) calculations have been carried out to assign the relevant electronic and vibrational features and to derive useful information about the molecular structure of these NLO‐phores.

Insulated polythiophenes with a polyrotaxane-like 3D architecture have shown excellent intrawire hole mobility, allowing their use in interesting optoelectronic applications. This is due to the isolation of the π-conjugated backbones that warrants for stabilization of the quasi-planar conformation of the polythiophene core and prevents electronic communication between adjacent chains. Thus, polythiophene-based insulated molecular wires (IMWs) constitute ideal test-beds to evaluate the structural changes within the conjugated polymer chain, such as intrachain conformation and π-electron delocalization. Here, we investigate the structure and spectroscopic response of fully and partially insulated polythiophene-based IMWs. An experimental investigation of Raman spectra supported by density functional theory (DFT) calculations allows us to give a detailed interpretation of intramolecular interactions, highlighting differences in π-electron conjugation revealed by the presence of an intensity transfer between the two main Raman modes associated with the C═C/C–C stretching vibrations. This study proves the sensitivity of Raman spectroscopy as a technique to monitor structural changes in self-encapsulated conjugated polymers.

Enantioselect‐DeFluor: Carbon–fluorine bond cleavage by a chiral zirconium complex allows the synthesis of optically active 1,3‐difluoroallene for the first time. Its absolute configuration was established by gas‐phase vibrational circular dichroism spectroscopy (see picture).

Enantioselect‐DeFluor: Die Spaltung einer Kohlenstoff‐Fluor‐Bindung durch einen chiralen Zirconiumkomplex ermöglichte die erste Synthese von optisch aktivem 1,3‐Difluorallen. Die absolute Konfiguration wurde durch Schwingungs‐Circulardichroismus‐Spektroskopie (VCD) in der Gasphase bestimmt (siehe Diagramm).

The first Diels–Alder cycloaddition of o-quinodimethane to SWNT has been performed under microwave irradiation.