| dc.identifier.uri | http://hdl.handle.net/11401/76288 | |
| dc.description.sponsorship | This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree. | en_US |
| dc.format | Monograph | |
| dc.format.medium | Electronic Resource | en_US |
| dc.language.iso | en_US | |
| dc.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dc.type | Dissertation | |
| dcterms.abstract | This dissertation consists of three projects: (1) Escape of Anions from Geminate Recombination due to Charge Delocalization. (2) Charge Separation of Electron-Hole Pairs (Exciplexes) Enhanced by Charge Delocalization. (3) Energies of Radical Anions Measured by Bimolecular Electron Transfer Equilibria Method. The first project studies geminate recombination of 23 radical anions (M*− ) with solvated protons (RH<sub>2</sub><super>+</super>) in tetrahydrofuran (THF). The recombination has two steps: (1) Diffusion of M<super>*− </super> and RH<sub>2</sub><super>+</super> together to form intimate (contact and solvent separated) ion pairs, driven by Coulomb attraction; (2) Annihilation of anions due to proton transfer (PT) from RH<sub>2</sub><super>+<super> to M<super>*− </super>. The kinetic analyses find that intimate ion pairs are formed in ~8 ns while the subsequent PT step can range from much faster (<0.5 ns) to as slow as 50 ns. A free ion yield Gfi = 0.69±0.06 per 100 eV, comprising ~29% of the total, was formed. This yield of " Type I" free ions is independent of the PT rate because it arises entirely by escape from the initial distribution of ion pair distances without forming intimate ion pairs. For 20 of the 23 molecules studied this is the only measurable source of free ions: once these anions enter intimate ion pairs the PT process annihilates all of them within detection limits. The three exceptions were anions of oligo(9,9-dihexyl)fluorenes, F<sub>n</sub><super>*− </super> (n=2-4). These three have PT rates similar to the slowest of the other 20 molecules, and have increased free ion yields. For these charge-delocalized anions, intimate ion-pairs are able to escape to form an additional yield of free ions, which may be termed " Type II" free ions. Protons attach to C and O atoms with a wide variety of PT rates providing opportunities to examine PT models, which discuss PT rate in terms of ∆ G<super>0</super>, PT coupling and the reorganization energy. While the Coulomb-bound ion pairs seem to offer an excellent vehicle for study of PT rates, the free energy correlation is scattered because different factors affect the rates and because knowledge of ∆ G<super>0</super> is inaccurate. An important observation is that no reaction transferring a proton to a C atom of M<super>*− </super> is diffusion controlled. The most important finding is the effect of low charge densities in highly charge-delocalized anions on PT rates and free ion yields. Based on the above findings, the influence of the charge delocalization on charge separation and potential energy of electron-hole pairs were studied with F<sub>n</sub>(n=1-6). Because charge delocalization of ions results in weak Coulomb attraction between opposite ions, potential energy of electron-hole pair increases with decreasing charge density. This weak Coulomb attraction also results in preference of solvent separated radical ion pair for electron-hole pairs. The recombination of electron-hole pair is an electron transfer (ET) reaction. In a simple two-state ET model, the rate of ET exponentially decreases with increasing separation distance <italic>r</italic> so the lifetime of electron-hole pair is increased. Due to the weak Coulomb attraction and long lifetime of electron-hole pair, the charge separation of electron-hole pair (the free ion yield) is enhanced. Reduction potentials (E<sub>red</sub>) of molecules were measured by combination of the bimolecular ET equilibria method and pulse radiolysis, which is capable of measuring E<sub>red</sub> for high reduction potential molecules and molecules with unstable anions. Pulse radiolysis is capable of rapidly reducing molecules in many solvent. The bimolecular ET method provides a window to estimate the equilibrium constant (K<sub>eq</sub>) of ET reactions. With K<sub>eq</sub> and E<sub>red</sub> of the reference molecule, E<sub>red</sub> of the subject molecule can be estimated. | |
| dcterms.abstract | This dissertation consists of three projects: (1) Escape of Anions from Geminate Recombination due to Charge Delocalization. (2) Charge Separation of Electron-Hole Pairs (Exciplexes) Enhanced by Charge Delocalization. (3) Energies of Radical Anions Measured by Bimolecular Electron Transfer Equilibria Method. The first project studies geminate recombination of 23 radical anions (M*− ) with solvated protons (RH<sub>2</sub><super>+</super>) in tetrahydrofuran (THF). The recombination has two steps: (1) Diffusion of M<super>*− </super> and RH<sub>2</sub><super>+</super> together to form intimate (contact and solvent separated) ion pairs, driven by Coulomb attraction; (2) Annihilation of anions due to proton transfer (PT) from RH<sub>2</sub><super>+<super> to M<super>*− </super>. The kinetic analyses find that intimate ion pairs are formed in ~8 ns while the subsequent PT step can range from much faster (<0.5 ns) to as slow as 50 ns. A free ion yield Gfi = 0.69±0.06 per 100 eV, comprising ~29% of the total, was formed. This yield of " Type I" free ions is independent of the PT rate because it arises entirely by escape from the initial distribution of ion pair distances without forming intimate ion pairs. For 20 of the 23 molecules studied this is the only measurable source of free ions: once these anions enter intimate ion pairs the PT process annihilates all of them within detection limits. The three exceptions were anions of oligo(9,9-dihexyl)fluorenes, F<sub>n</sub><super>*− </super> (n=2-4). These three have PT rates similar to the slowest of the other 20 molecules, and have increased free ion yields. For these charge-delocalized anions, intimate ion-pairs are able to escape to form an additional yield of free ions, which may be termed " Type II" free ions. Protons attach to C and O atoms with a wide variety of PT rates providing opportunities to examine PT models, which discuss PT rate in terms of ∆ G<super>0</super>, PT coupling and the reorganization energy. While the Coulomb-bound ion pairs seem to offer an excellent vehicle for study of PT rates, the free energy correlation is scattered because different factors affect the rates and because knowledge of ∆ G<super>0</super> is inaccurate. An important observation is that no reaction transferring a proton to a C atom of M<super>*− </super> is diffusion controlled. The most important finding is the effect of low charge densities in highly charge-delocalized anions on PT rates and free ion yields. Based on the above findings, the influence of the charge delocalization on charge separation and potential energy of electron-hole pairs were studied with F<sub>n</sub>(n=1-6). Because charge delocalization of ions results in weak Coulomb attraction between opposite ions, potential energy of electron-hole pair increases with decreasing charge density. This weak Coulomb attraction also results in preference of solvent separated radical ion pair for electron-hole pairs. The recombination of electron-hole pair is an electron transfer (ET) reaction. In a simple two-state ET model, the rate of ET exponentially decreases with increasing separation distance <italic>r</italic> so the lifetime of electron-hole pair is increased. Due to the weak Coulomb attraction and long lifetime of electron-hole pair, the charge separation of electron-hole pair (the free ion yield) is enhanced. Reduction potentials (E<sub>red</sub>) of molecules were measured by combination of the bimolecular ET equilibria method and pulse radiolysis, which is capable of measuring E<sub>red</sub> for high reduction potential molecules and molecules with unstable anions. Pulse radiolysis is capable of rapidly reducing molecules in many solvent. The bimolecular ET method provides a window to estimate the equilibrium constant (K<sub>eq</sub>) of ET reactions. With K<sub>eq</sub> and E<sub>red</sub> of the reference molecule, E<sub>red</sub> of the subject molecule can be estimated. | |
| dcterms.available | 2017-09-20T16:49:57Z | |
| dcterms.contributor | Miller, John R. | en_US |
| dcterms.contributor | Rafailovich, Miriam | en_US |
| dcterms.contributor | Welch, David | en_US |
| dcterms.contributor | Wishart, James. | en_US |
| dcterms.creator | Chen, Hung Cheng | |
| dcterms.dateAccepted | 2017-09-20T16:49:57Z | |
| dcterms.dateSubmitted | 2017-09-20T16:49:57Z | |
| dcterms.description | Department of Materials Science and Engineering. | en_US |
| dcterms.extent | 144 pg. | en_US |
| dcterms.format | Application/PDF | en_US |
| dcterms.format | Monograph | |
| dcterms.identifier | http://hdl.handle.net/11401/76288 | |
| dcterms.issued | 2014-12-01 | |
| dcterms.language | en_US | |
| dcterms.provenance | Made available in DSpace on 2017-09-20T16:49:57Z (GMT). No. of bitstreams: 1
Chen_grad.sunysb_0771E_12092.pdf: 4794126 bytes, checksum: 6a56d401345e8b8566e16e8e3bb421ba (MD5)
Previous issue date: 1 | en |
| dcterms.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dcterms.subject | Electron Transfer, Oligofluorene, Proton Transfer, Pulse Radiolysis, Radiation Chemistry, Recombination | |
| dcterms.subject | Physical chemistry | |
| dcterms.title | Recombination of Charge Carriers in Low Dielectric Constant Organic Solvent | |
| dcterms.type | Dissertation | |
