Vincent Liégeois

An analytical derivative procedure for the calculation of vibrational Raman optical activity spectra

We present an analytical time-dependent Hartree-Fock algorithm for the calculation of the derivatives of the electric dipole-magnetic dipole polarizability with respect to atomic Cartesian coordinates. Combined with analogous procedures to determine the derivatives of the electric dipole-electric dipole and electric dipole-electric quadrupole polarizabilities, it enables a fully analytical evaluation of the three frequency-dependent vibrational Raman optical activity (VROA) invariants within the harmonic approximation. The procedure employs traditional non-London atomic orbitals, and the gauge-origin dependence of the VROA intensities has, therefore, been assessed for the commonly used aug-cc-pVDZ and rDPS:3-21G basis sets.

TDHF Evaluation of the Dipole-Quadrupole Polarizability and Its Geometrical Derivatives.

Analytical procedures based on the time-dependent Hartree-Fock (TDHF) scheme are elaborated to evaluate the frequency-dependent electric dipole-electric quadrupole polarizability and its derivatives with respect to atomic Cartesian coordinates. On one hand, the mixed second-order TDHF equations are solved iteratively to obtain the second-order derivatives of the linear combination of atomic orbitals coefficients, once with respect to atomic Cartesian coordinates and once with respect to external dynamic electric fields or electric field gradients. On the other hand, taking advantage of the 2n + 1 rule, the first-order derivatives of A are expressed with respect to atomic Cartesian coordinates in terms of lower-order derivatives. These procedures have been implemented in the GAMESS quantum chemistry package and have been illustrated in the case of several small molecules as well as adamantane.

Enhanced open-circuit voltage in polymer solar cells by dithieno[3,2-b:2′,3′-d]pyrrole N-acylation

A series of low bandgap copolymers composed of N-acyl-substituted dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) as the electron rich donor constituents (with various alkyl side chain patterns) combined with different electron deficient acceptor building blocks are developed for polymer solar cell applications. Due to the introduction of the N-acyl substituents, the HOMO energy levels of the push–pull copolymers decrease as compared to the N-alkyl-DTP analogues, resulting in an increased open-circuit voltage (Voc) and hence solar cell performance. For an N-acyl-DTP-alt-thieno[3,4-c]pyrrole-4,6-dione (PDTP-TPD) copolymer a bulk heterojunction device with a Voc up to 0.80 V and a power conversion efficiency of 4.0% is obtained, the highest value for DTP-based polymer materials to date. Moreover, by implementation of a conjugated polyelectrolyte cathode interlayer the short-circuit current noticeably increases, enhancing the solar cell efficiency to 5.8%.

Vibrational Raman optical activity of pi-conjugated helical systems: Hexahelicene and heterohelicenes.

Helicenes constitute a special class of molecules combining helical conformation with π‐electron delocalization. These confer to helicenes specific chirooptical properties. In this article, we investigate the vibrational signatures thanks to the simulation of vibrational Raman optical activity (VROA) spectra. For that, four representative helicenes: hexahelicene, tetrathia‐[7]‐helicene, and its pyrrole and furan analogs have been simulated and interpreted using a recently implemented analytical scheme. Helicenes show intense VROA peaks attributed to their π‐conjugated structure and associated with collective vibrational modes. In hexahelicene, the dominant VROA features are due to vibrational modes involving motions of the carbon skeleton and H‐wagging, but the intensity finds its source almost exclusively in the former. In the case of the three heterohelicenes, the previous statement is also verified, and on changing the heteroatoms, similar modes presenting comparable atomic contribution patterns have been highlighted, though the vibrational and electronic properties are modified. Some fingerprints could therefore be associated with the helicity of the system. In particular, in forward spectra, most of the VROA bands are positive for left‐handed helicenes. Nevertheless, the spectral patterns are quite complex, and no easy rule‐of‐thumb could distinguish between the different heterohelicenes. Then, considering the fact that most of the contributions originate from the C atoms (group coupling matrices decomposition), it can be concluded that the major role of the heteroatom is restricted to modifying the geometry and the normal modes. At last, the small impact of the gauge‐origin on the calculated spectra using a relatively modest basis set (rDPS:3‐21G) is demonstrated here in the case of the tetrathia‐[7]‐helicene molecule presenting a C2 symmetry. This further demonstrates the adequacy of this basis set for VROA calculations.

Implementation in the Pyvib2 program of the localized mode method and application to a helicene

In this paper, after reviewing key elements for simulating and interpreting IR, Raman, VCD, and ROA spectra, as well as after describing the localized mode procedure, we present a graphical user interface to carry out the normal mode localizations and we illustrate its application on the ROA spectra of the [19]helicene molecule. The overall procedure consists of four steps, and therefore, a specific interface has been designed for each of them. The first and most important part of the procedure is the selection of the mode ensemble under which the localization procedure is performed. Then, during our step-by-step guided tour of the localized mode procedure in Pyvib2, we highlight the importance of the ordering of the localized modes and the importance to set correctly the phase factor between the localized modes. Finally, the vibrational coupling matrix (

Analysis of Vibrational Raman Optical Activity Signatures of the (TG)N and (GG)N Conformations of Isotactic Polypropylene Chains in Terms of Localized Modes

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Beta Sheets with a Twist: The Conformation of Helical Polyisocyanopeptides Determined by Using Vibrational Circular Dichroism

), the intensity coupling matrix (