Extension of Conjugation Leading to Bathochromic or Hypsochromic Effects in OPV Series

Abstract

Four OPV series 1-4 (a-d) with a terminal dialkylamino group as electron donor were prepared by Wittig-Horner reactions. To study the influence of the push-pull effect on the long-wavelength absorption, three of the four series contained terminal acceptor groups (CN, CHO, NO(2)). The length of the chromophores strongly affects the intramolecular charge transfer (ICT)-an effect which superimposes upon the extension of the conjugation. Increasing numbers n of repeat units cause an overall bathochromic shift for the purely donor-substituted series 1 a-4 a and the series 1 b-4 b with CN as weak acceptor. The two effects annihilate each other in the series 1 c-4 c with terminal CHO groups, so that the absorption maxima are almost independent of the length of the chromophore. A hypsochromic shift is observed for the series 1 d-4 d, which contains the strong acceptor group NO(2). This anomaly disappears on protonation of the dialkylamino group because the push-pull effect disappears in the ammonium salts. The results can be explained by semiempirical quantum mechanics (AM1, INDO/S). The HOMO-LUMO transition, which is mainly responsible for the ICT, becomes less important in the electron transitions S(0)-->S(1) when the distance between donor and acceptor is increased. The commonly used VB model, which contains an electroneutral and a zwitterionic resonance structure, is contrasted with a MO model with dipole segments at both ends of the OPV chains. The latter model turned out to be more appropriate-at least for donor-acceptor-substituted OPVs with n >/= 2.

Advanced opto-electronics materials by fullerene and acetylene scaffolding

“…Computational studies actually revealed that within this series of constitutional isomers, the variance in the lowest-energy transitions is caused by differences in the HOMO (highest occupied molecular orbital) energy, which is highest in the cross-conjugated system. It became apparent, therefore, in this investigation that the correlation between the position of λ max in the UV/vis spectra and the effectiveness of different conjugation pathways is not always valid; a conclusion also reached by others [51,52]. For compounds with strong donor and acceptor moieties, the λ max in the UV/vis spectrum should only be considered as a measure of the change of the degree of CT in the transition from the ground state to the excited state, and should not be used for the study of conjugation effectiveness.…”

Impact of Donor–Acceptor Functionalization on the Properties of Linearly π-Conjugated Oligomers: Establishing Quantitative Relationships for the Substituent and Substituent Cooperative Effect Based on Quantum Chemical Calculations

“…In this work, we show along with other investigators 3,8,[10][11][12][13][14][15]25 , that the overall response of the properties of π-conjugated compounds to donor-acceptor substitution can be expressed by means of simple analytical expressions. In earlier work 27 , we also showed that part of the response of a given property can be ascribed to substituent cooperative effects, i.e.…”

“…Concepts such as Effective Conjugation Length (ECL) 8 , Confinement Length (CL) 9 or Delocalisation Length (DL) 9 , which address the issues related to the saturation of a particular property with respect to the conjugation length, emerged. At the same time, Quantitative Structure-Property Relationships (QSPR) that model the dependence of molecular properties on chain size and substitution pattern were established 3,8,[10][11][12][13][14][15][16][17][18][19][20][21][22] . In this context, Meier et al were able to express the dependence of the longest wavelength of absorption (λ max ) on chain length for donor-acceptor substituted polyacetylene 3 .…”

“…Brédas et al 3,8,[10][11][12][13][14][15] describing the response of these properties to chain length extension and to the substitution pattern. These expressions will show at what rate the substituent impact will vanish for a given type of backbone, and how rapidly the ECL for that particular property will be reached.…”

Konjugierte Oligomere mit terminaler Donor‐Acceptor‐Substitution

“…Da langkettige Dialkylamino-Reste gute Solubilisierungseigenschaften haben, konnte eine systematische Studie mit den Oligo(1,4-phenylenvinylenen) (OPV) 5 a-e, 6 a-e, 7 a-e und 8 a-e durchgeführt werden. [21,25] Ausgehend von 9 wurde zunächst mithilfe der WittigHorner-Reaktion und einer einfachen Schutzgruppentechnik die Reihe 5 c-8 c aufgebaut (Schema 5), wobei das Phosphonat 10 als "Verlängerungsreagens" fungierte. Nach der basischen Kondensation erfolgte unmittelbar bei der sauren Aufarbeitung die Entschützung der von 10 eingebrachten Abbildung 3.…”