{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/138798"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/138798","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"The Role of Charge Transfer Induced Spin Crossover Complexes on Charge-Separated State Lifetime in Photoelectrochemical Devices","abstract":"In sustainable fuel production, the conversion of solar energy into chemical energy is one of the great interests of storing high-density energy. The relatively low observed quantum yields (~19%) for such process compared to theoretical efficiencies (in the range of 30-40%, depending on target reaction) result in part from the prevalent short-lived photo-induced charge-separated states. In our previous studies, manganese (II/III) poly(pyrazolyl)borate (Mn(pzb)2) complexes demonstrated exceptional charge-separated-state lifetimes in the dye-sensitized photoanode constructs. Mn(pzb)2 undergoes a spin transition from a high-spin, sextet state for Mn(II), to a low-spin, triplet state for Mn(III). The spin change is induced upon a pseudo-octahedral-to-octahedral structural change that modifies the orbital overlap between the pyrazolyl lone pair and central Mn. The large reorganization energy associated with the structural and spin transitions increased the lifetime of charge-separated states. Inspired from the results, we sought to determine the degree of molecular reorganization/spin transition that results in the greatest modulation in back electron transfer rates. Two methods were explored 1) the use of zwitterionic ligands, 2) the formation of a multi-component molecularly sensitized interface with [M(pzb)2] (M= Mn, Fe, and Co). In the first approach, the Lewis base of the zwitterion ligand affects redox potential and the magnetic properties. By tuning the pKa of the Lewis base and the functional group on pyrazole, the extent of the spin transition can be modified. Moreover, the zwitterion ligand is charge-neutral and a counterion is needed to balance the Mn positive charge. Thus, the overall charge neutral zwitterionic [Mn(pzb)2] complex has improved its solubility in organic solvents, a downfall of our first public [M(pzb)2] complex derivation in quantum dot solar cell. The second approach is to decorate the [M(pzb)2] (M= Mn, Fe and Co) with phosphoric acid group (-PO3H2) to form a self-assembly layer with a cognizant chromophore. [M(pzb)2] (M= Mn, Fe and Co) exhibit charge transfer induced spin crossover (CTISC) but the change of spin multiplicity is different depending on the central metal. The spin multiplicity difference were hypothesized to manipulate the extent spin transition/reorganization. Furthermore, the self-assembled layer forms the molecular layer in the photoanode construct, which bypasses the aforementioned solubility issue.","abstract_html":"In sustainable fuel production, the conversion of solar energy into chemical energy is one of the great interests of storing high-density energy. The relatively low observed quantum yields (~19%) for such process compared to theoretical efficiencies (in the range of 30-40%, depending on target reaction) result in part from the prevalent short-lived photo-induced charge-separated states. In our previous studies, manganese (II/III) poly(pyrazolyl)borate (Mn(pzb)2) complexes demonstrated exceptional charge-separated-state lifetimes in the dye-sensitized photoanode constructs. Mn(pzb)2 undergoes a spin transition from a high-spin, sextet state for Mn(II), to a low-spin, triplet state for Mn(III). The spin change is induced upon a pseudo-octahedral-to-octahedral structural change that modifies the orbital overlap between the pyrazolyl lone pair and central Mn. The large reorganization energy associated with the structural and spin transitions increased the lifetime of charge-separated states. Inspired from the results, we sought to determine the degree of molecular reorganization/spin transition that results in the greatest modulation in back electron transfer rates. Two methods were explored 1) the use of zwitterionic ligands, 2) the formation of a multi-component molecularly sensitized interface with [M(pzb)2] (M= Mn, Fe, and Co). In the first approach, the Lewis base of the zwitterion ligand affects redox potential and the magnetic properties. By tuning the pKa of the Lewis base and the functional group on pyrazole, the extent of the spin transition can be modified. Moreover, the zwitterion ligand is charge-neutral and a counterion is needed to balance the Mn positive charge. Thus, the overall charge neutral zwitterionic [Mn(pzb)2] complex has improved its solubility in organic solvents, a downfall of our first public [M(pzb)2] complex derivation in quantum dot solar cell. The second approach is to decorate the [M(pzb)2] (M= Mn, Fe and Co) with phosphoric acid group (-PO3H2) to form a self-assembly layer with a cognizant chromophore. [M(pzb)2] (M= Mn, Fe and Co) exhibit charge transfer induced spin crossover (CTISC) but the change of spin multiplicity is different depending on the central metal. The spin multiplicity difference were hypothesized to manipulate the extent spin transition/reorganization. Furthermore, the self-assembled layer forms the molecular layer in the photoanode construct, which bypasses the aforementioned solubility issue.","abstract_has_math":false,"creators":["Cheng, Tzu-Ching"],"institution":"Virginia Tech","degree_name":"Doctor of Philosophy","degree_level":"doctoral","degree_discipline":"Materials Science and Engineering","degree_department":"Materials Science and Engineering","school":null,"contributors":[],"advisors":[],"committee_chairs":["Morris, Amanda"],"committee_members":["Saouma, Caroline Thalia Abdunnur","Slebodnick, Carla","Tallon Galdeano, Carolina"],"year":2025,"date_issued":"2025-10-28","date_published":"2025-10-28","updated_at":"2026-07-22T22:19:07Z","subjects":["Photovoltaics","Spin-Crossover","Self-assembly Layers","Electron Transfer Dynamic","Recombination Dynamic"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:44831"],"render_values":[{"text":"vt_gsexam:44831","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/138798","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Morris, Amanda"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Saouma, Caroline Thalia Abdunnur","Slebodnick, Carla","Tallon Galdeano, Carolina"]},{"key":"dc:contributor.department","label":"Department","values":["Materials Science and Engineering"]},{"key":"dc:creator","label":"Author","values":["Cheng, Tzu-Ching"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-10-29T08:00:22Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-10-29T08:00:22Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-10-28"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science and Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Photovoltaics","Spin-Crossover","Self-assembly Layers","Electron Transfer Dynamic","Recombination Dynamic"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:44831"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/138798"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["In sustainable fuel production, the conversion of solar energy into chemical energy is one of the great interests of storing high-density energy. The relatively low observed quantum yields (~19%) for such process compared to theoretical efficiencies (in the range of 30-40%, depending on target reaction) result in part from the prevalent short-lived photo-induced charge-separated states. In our previous studies, manganese (II/III) poly(pyrazolyl)borate (Mn(pzb)2) complexes demonstrated exceptional charge-separated-state lifetimes in the dye-sensitized photoanode constructs. Mn(pzb)2 undergoes a spin transition from a high-spin, sextet state for Mn(II), to a low-spin, triplet state for Mn(III). The spin change is induced upon a pseudo-octahedral-to-octahedral structural change that modifies the orbital overlap between the pyrazolyl lone pair and central Mn. The large reorganization energy associated with the structural and spin transitions increased the lifetime of charge-separated states. Inspired from the results, we sought to determine the degree of molecular reorganization/spin transition that results in the greatest modulation in back electron transfer rates. Two methods were explored 1) the use of zwitterionic ligands, 2) the formation of a multi-component molecularly sensitized interface with [M(pzb)2] (M= Mn, Fe, and Co). In the first approach, the Lewis base of the zwitterion ligand affects redox potential and the magnetic properties. By tuning the pKa of the Lewis base and the functional group on pyrazole, the extent of the spin transition can be modified. Moreover, the zwitterion ligand is charge-neutral and a counterion is needed to balance the Mn positive charge. Thus, the overall charge neutral zwitterionic [Mn(pzb)2] complex has improved its solubility in organic solvents, a downfall of our first public [M(pzb)2] complex derivation in quantum dot solar cell. The second approach is to decorate the [M(pzb)2] (M= Mn, Fe and Co) with phosphoric acid group (-PO3H2) to form a self-assembly layer with a cognizant chromophore. [M(pzb)2] (M= Mn, Fe and Co) exhibit charge transfer induced spin crossover (CTISC) but the change of spin multiplicity is different depending on the central metal. The spin multiplicity difference were hypothesized to manipulate the extent spin transition/reorganization. Furthermore, the self-assembled layer forms the molecular layer in the photoanode construct, which bypasses the aforementioned solubility issue."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["To advance next-generation renewable fuels, it is essential to understand how electron transfer across interfaces is governed. Presented herein are strategies for generating chemically relevant, long-lived charge-separated states. The charge-separated state is critical for transforming fleeting light excitation into storable, usable chemical/electrical energy. Such states arise through electronic reorganization at a metal center following electron transfer. The dissertation details the synthesis and characterization of novel metal complexes that undergo this reorganization, providing deeper insight into how it promotes the stabilization of long-lived charge-separated states. The findings aim to inspire new approaches in the design of catalytic materials for light-driven chemical transformations."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Doctor of Philosophy"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["The Role of Charge Transfer Induced Spin Crossover Complexes on Charge-Separated State Lifetime in Photoelectrochemical Devices"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Morris, Amanda"],"dc:contributor.committeemember":["Saouma, Caroline Thalia Abdunnur","Slebodnick, Carla","Tallon Galdeano, Carolina"],"dc:contributor.department":["Materials Science and Engineering"],"dc:creator":["Cheng, Tzu-Ching"],"dc:date.accessioned":["2025-10-29T08:00:22Z"],"dc:date.available":["2025-10-29T08:00:22Z"],"dc:date.issued":["2025-10-28"],"dc:description.abstract":["In sustainable fuel production, the conversion of solar energy into chemical energy is one of the great interests of storing high-density energy. The relatively low observed quantum yields (~19%) for such process compared to theoretical efficiencies (in the range of 30-40%, depending on target reaction) result in part from the prevalent short-lived photo-induced charge-separated states. In our previous studies, manganese (II/III) poly(pyrazolyl)borate (Mn(pzb)2) complexes demonstrated exceptional charge-separated-state lifetimes in the dye-sensitized photoanode constructs. Mn(pzb)2 undergoes a spin transition from a high-spin, sextet state for Mn(II), to a low-spin, triplet state for Mn(III). The spin change is induced upon a pseudo-octahedral-to-octahedral structural change that modifies the orbital overlap between the pyrazolyl lone pair and central Mn. The large reorganization energy associated with the structural and spin transitions increased the lifetime of charge-separated states. Inspired from the results, we sought to determine the degree of molecular reorganization/spin transition that results in the greatest modulation in back electron transfer rates. Two methods were explored 1) the use of zwitterionic ligands, 2) the formation of a multi-component molecularly sensitized interface with [M(pzb)2] (M= Mn, Fe, and Co). In the first approach, the Lewis base of the zwitterion ligand affects redox potential and the magnetic properties. By tuning the pKa of the Lewis base and the functional group on pyrazole, the extent of the spin transition can be modified. Moreover, the zwitterion ligand is charge-neutral and a counterion is needed to balance the Mn positive charge. Thus, the overall charge neutral zwitterionic [Mn(pzb)2] complex has improved its solubility in organic solvents, a downfall of our first public [M(pzb)2] complex derivation in quantum dot solar cell. The second approach is to decorate the [M(pzb)2] (M= Mn, Fe and Co) with phosphoric acid group (-PO3H2) to form a self-assembly layer with a cognizant chromophore. [M(pzb)2] (M= Mn, Fe and Co) exhibit charge transfer induced spin crossover (CTISC) but the change of spin multiplicity is different depending on the central metal. The spin multiplicity difference were hypothesized to manipulate the extent spin transition/reorganization. Furthermore, the self-assembled layer forms the molecular layer in the photoanode construct, which bypasses the aforementioned solubility issue."],"dc:description.abstractgeneral":["To advance next-generation renewable fuels, it is essential to understand how electron transfer across interfaces is governed. Presented herein are strategies for generating chemically relevant, long-lived charge-separated states. The charge-separated state is critical for transforming fleeting light excitation into storable, usable chemical/electrical energy. Such states arise through electronic reorganization at a metal center following electron transfer. The dissertation details the synthesis and characterization of novel metal complexes that undergo this reorganization, providing deeper insight into how it promotes the stabilization of long-lived charge-separated states. The findings aim to inspire new approaches in the design of catalytic materials for light-driven chemical transformations."],"dc:description.degree":["Doctor of Philosophy"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:44831"],"dc:identifier.uri":["https://hdl.handle.net/10919/138798"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Photovoltaics","Spin-Crossover","Self-assembly Layers","Electron Transfer Dynamic","Recombination Dynamic"],"dc:title":["The Role of Charge Transfer Induced Spin Crossover Complexes on Charge-Separated State Lifetime in Photoelectrochemical Devices"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Materials Science and Engineering"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:07Z"}