Electronic Excitations And Alternation Of Conjugated Polymers

The electronic excitations and fluorescence of conjugated polymers are related to large or small alternation δ of the transfer integrals t(1 ± δ) along the backbone. The fluorescence of polysilanes (PSs) and poly (para-phenylenevinylene (PPV) is linked to large δ, which places the one-photon gap Eg below the lowest two-photon gap Ea and reduces distortions due to electron-phonon (e-p) coupling. In contrast to small δ ∼ 0.1 in π-conjugated polymers, such as polyacetylene (PA), para-conjugated phenyls lead to an extended π-system with increased alternation, to states localized on each ring and to charge-transfer excitations between them. Surprisingly good agreement is found between semiempirical parametric method 3 (PM3) bond lengths and exact Pariser-Parr-Pople (PPP) π-bond orders for trans-stilbene, where the PPV bipolarons are confined to two phenyls. Stilbene spectra are consistent with increased alternation and small e-p distortions. © 1993.5401/03/153547DIB; Dirección de Investigación, Universidad Nacional de ColombiaHeeger, Kivelson, Schrieffer, Su, (1988) Rev. Mod. Phys., 60, p. 781Skotheim, (1986) Handbook of Conducting Polymers, 1-2. , Marcel Dekker, New York(1991) Synth. Met., 41-43(1988) Synth. Met., 27-29Baughman, Brédas, Chance, Elsenbaumer, Shacklette, (1982) Chem. Rev., 82, p. 209Soos, Etemad, Galvao, Ramasesha, (1992) Chem. Phys. Lett., 194, p. 341Miller, Michl, (1989) Chem. Rev., 89, p. 1359Zeigler, Fearon, (1990) Silicon-Based Polymer Science: A Comprehensive Resource, ACS Symposium Series 381, , American Chemical Society, Washington, DCSandorfy, LCAO MO CALCULATIONS ON SATURATED HYDROCARBONS AND THEIR SUBSTITUTED DERIVATIVES (1955) Canadian Journal of Chemistry, 33, p. 1337Soos, Hayden, (1990) Chem. Phys., 143, p. 199Soos, Kepler, (1991) Phys. Rev. B, 43, p. 11908Kepler, Seager, Soos, McWilliams, (1992) Synth. Met., 50, p. 387Elschner, Mart, Pautmeier, Bässler, Stolka, McGrane, (1991) Chem. Phys., 150, p. 81Rauscher, Bässler, Bradley, Hennecke, (1990) Phys. Rev. B, 42, p. 9830Walsh, Ambrose, Burland, Miller, Tinto, (1992) Inorg. Organomet. Polym., 2, p. 285Ito, Terazima, Azumi, (1990) J. Am. Chem. Soc., 112, p. 444Kepler, Soos, (1991) Phys. Rev. B, 43, p. 12530Hudson, Kohler, Schulten, (1982) Excited States, 6, p. 1. , E. Lim, Academic Press, Orlando, FLSoos, Hayden, (1988) Electroresponsive Molecular and Polymeric Systems, 1, p. 197. , T.A. Skotheim, Marcel Dekker, New YorkBondeson, Soos, (1979) J. Chem. Phys., 71, p. 3807Bondeson, Soos, (1980) J. Chem. Phys., 73, p. 598Bondeson, Soos, (1979) Chem. Phys., 44, p. 403Ovchinnikov, (1970) Sov. Phys. JETP, 30, p. 1160Hayden, Soos, (1988) Phys. Rev. B, 38, p. 6075Colaneri, Bradley, Friend, Burns, Holmes, Spangler, (1990) Phys. Rev. B, 42, p. 11670Burroughes, Bradley, Brown, Marks, MacKay, Friend, Bruns, Holmes, (1990) Nature (London), 347, p. 539Swanson, Lane, Shinar, Wudl, (1991) Phys. Rev. B, 44, p. 10617Kasha, (1950) Discuss. Faraday Soc., 9, p. 14Soos, Hayden, (1989) Synth. Met., 28, p. D543Patil, Heeger, Wudl, (1988) Chem. Rev., 88, p. 183Periasamy, Danieli, Ruani, Zamboni, Taliani, (1992) Phys. Rev. Lett., 68, p. 919Soos, Ramasesha, Valence-bond theory of linear Hubbard and Pariser-Parr-Pople models (1989) Physical Review B, 29, p. 5410Z. G. Soos, S. Ramasesha and D. S. Galvão, Phys. Rev. B, in pressLhost, Brédas, (1992) J. Chem. Phys., 96, p. 5279Stewart, Optimization of parameters for semiempirical methods I. Method (1989) Journal of Computational Chemistry, 10, p. 209Stewart, Optimization of parameters for semiempirical methods II. Applications (1989) Journal of Computational Chemistry, 10, p. 221Scano, Thompson, Comparison of semiempirical MO methods applied to large molecules (1991) Journal of Computational Chemistry, 12, p. 172Herkstroeter, McClure, (1968) J. Am. Chem. Soc., 90, p. 4522Suzuki, Koyano, Kunii, (1972) Bull. Chem., Jpn., 45, p. 1972Coulson, The Electronic Structure of Some Polyenes and Aromatic Molecules. VII. Bonds of Fractional Order by the Molecular Orbital Method (1939) Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 169, p. 413Dyck, McClure, (1962) J. Chem. Phys., 36, p. 2326Walczak, Stucky, (1976) J. Am. Chem. Soc., 98, p. 553