Conjugated exciton model

D McBranch, MB Sinclair. Ultrafast photoinduced absorption in nondegenerate ground-state conjugated polymers Signatures of excited states. In NS Sariciftci, ed. Nature of the Photoexcitations in Conjugated Polymers Semiconductor Band vs. Exciton Model, New York World Scientific, 1997. 

Whether conjugated polymers are best described by a band model, such as the SSH model, or an exciton model, will depend crucially on the relative strengths of the electron-phonon and electron-electron interactions. After the discovery of highly conductive polymers, the band model was widely accepted and applied to the interpretation of experimental data. Gradually since that time, evidence that suggests that an exciton picture is more appropriate has been accumulating. Comparison of experimental results with the models described above has been used to estimate the relative importance of the two types of interaction. This will be discussed in the following sections. 

These fits, although excellent, do not mle out the alternative exciton model. To judge which better describes the data, one needs a similar critical comparison between theory and experiment based on the exciton model. When such a quantitative comparison is made, one finds a fundamental discrepancy between the exciton model and the experimental results The exciton model predicts a symmetric absorption lineshape for oriented materials in which the conjugated polymer is chain aligned and chain extended. 

Beljonne, D., J. Cornil, R. Silbey, P. Millie, and J.L. Bredas. 2000. Interchain interactions in conjugated materials The exciton model versus the supermolecular approach. / Chem Phys 112 4749. 

We evaluate this matrix element using the effective-particle exciton model introduced in Chapter 6. We briefly review this theory here. In the weak-couphng limit (namely, the limit that the Coulomb interactions are less than or equal to the band width) the intramolecular excited states of semiconducting conjugated polymers are Mott-Wannier excitons described by,... 

Primary Photoexcitations in Conjugated Polymers Molecular Exciton versus Semiconductor Band Model (Ed. N.S. Sariciftci) World Scientific, Singapore 1997. 

The role of disorder in the photophysics of conjugated polymers has been extensively described by the work carried out in Marburg by H. Bassler and coworkers. Based on ultrafast photoluminescence (PL) (15], field-induced luminescence quenching [16J and site-selective PL excitation [17], a model for excited state thermalizalion was proposed, which considers interchain exciton migration within the inhomogenously broadened density of states. We will base part of the interpretation of our results in m-LPPP on this model, which will be discussed in some detail in Sections 8.4 and 8.6. 

Yaron, D., Moore, E.E., Shuai, Z., Bredas, J.L. Comparison of density matrix renormalization group calculations with electron-hole models of exciton binding in conjugated polymers. J. Chem. Phys. 1998, 108(17), 7451. 

Sariciftci NS (1997) Primary photoexcitations in conjugated polymers molecular exciton versus semiconductor band model. Word Scientific, Singapore... 

In thin films of electroluminescent conjugated polymers, Kanner et al. [12] and Yan et al. [13] explained the quenching of PL by invoking an exciton migration mechanism to nonradiative traps based on the Balagurov-Vaks model [14], The survival probability of an exciton on a 1-D lattice (fi- = 1/3) is characterized by a diffusion time t(i. For times t t,i. the PL intensity follows... 

B. Mennucci, J. Tomasi and R. Cammi, Excitonic splitting in conjugated molecular materials A quantum mechanical model including interchain interactions and dielectric effects, Phys. Rev. B, 70 (2004) 205212. 

The perturbative IEFPCM-LR model has been applied to study EET between molecules in liquid solutions [26-28] and at liquid/gas interfaces [29], and to the exciton splitting in conjugated molecular materials [30],... 

These results, and also the failure of the exciton coupling model in reproducing the CD spectra of (R)-(+)-56, were consistent with weak, but still significant, conjugation between naphthalene moieties. Notably, dihedral angles of 70° were found between naphthalene moieties in the X-ray structure of enantiopure (R)-(+)-56. Carbodianion (R)-562. 2M+ (M = Li, Na) was prepared via reduction of (R)-(+)-56 with alkali metals gave carbodianion (R)-562. 2M+ (M = Li, Na) no intermediate radical anion could be detected or isolated, in agreement with the cyclic voltammetric data [101]. 

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