Structure and Optical Absorption of Oligo(p- and m-phenylenevinylenes) and Their Radical Anions: A Comparative Theoretical Study

Abstract

We report on a comparative quantum-chemical study of oligo@-and m-phenyleneviny1ene)s (OPPV and OMPV, respectively) isomers and their radical anions in order to explain their optical absorption spectra. The AM1 semiempirical approach is employed to assess the structural changes from neutral to monocharged states.The optimized geometries are further used in PPP-CI calculations of the optical transitions for the closed and open shell n-systems. With increasing number of repeat units, OPPV exhibits significant splitting of the frontier n-states, which remain almost degenerate for OMPV. As a consequence, reduction is found to result in an extended charged defect for the former oligomers. In contrast, self-trapping of the excess charge into a single stilbene unit is predicted for OMPV. This result serves further as a basis to reproduce and interpret in detail the several characteristic absorptions of the title compounds.

Transient absorption spectra of triplet states and charge carriers of conjugated polymers

“…The absorption maximum is in good agreement with theoretical predictions [55]. In agreement with this assignment, the transient decays fairly rapidly in the presence of oxygen due to a chemical reaction, as expected for a typical organic radical anion [56].…”

Spirobifluorene Regioisomerism: A Structure–Property Relationship Study

“…[30] Indeed, it is admitted that there is a better delocalisation of π-electrons following the para/ortho/meta sequence and numbers of studies have tried to elucidate the origin of the restricted π-conjugation between para, ortho and meta substituted oligophenylenes. [30][31][32][33][34][35][36] In our case, it is clear that 3 displays a different behaviour compared to its building block meta terphenyl as it presents a relatively intense degree of conjugation between the phenyl and the fluorene. Thus, the 'linkage' effect cannot explain by itself this feature and other parameters should be invoked.…”

Optical Bandgaps of π‐Conjugated Organic Materials at the Polymer Limit: Experiment and Theory

“…In quantum-chemical approaches, such as the "free electron gas model" (H. Kuhn, 1958), [63] the Hückel model, [50,64] and the Peierls-Hubbard model, [54,65] the correct evolution of the transition energies with respect to 1/N is obtained by accounting for electron interaction through the introduction of bond alternation parameters in the expression of the resonance or transfer integrals. [66] The correct chainlength dependence is also found with more sophisticated quantum-chemical methods (where electron interaction is explicitly considered), such as the semiempirical Hartree-Fock intermediate neglect of differential overlap (ZINDO) method, as parameterized by Zerner and co-workers, [67,68] PPP (Pariser-Parr-Pople) [69,70] methods, or with ab initio HartreeFock approaches coupled to a CIS scheme. [71] Density functional theory (DFT) calculations generally tend to overestimate long-range electron correlation effects, [72] leading to a deviation from the linear behavior only for n > 10, [73] as also described in Section 4.2.…”