Organic Materials for Electro-Optic and Optoelectronic Applications: Understanding Structure – Property Relationships

• Main Author: Kosilkin, Ilya V
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2012
• Subjects: Chemistry; Materials science; Organic chemistry
• ISBN: 1267285230; 9781267285232

Organic materials are promising candidates for application to electro-optics (EO) due to such advantages as tunable properties, ease of processability and the possibility of chip-scale integration. To achieve EO activity on a bulk level, noncentrosymmetric alignment of chromophores is required. However, modern chromophores with high first-order molecular hyperpolarizability have large ground state dipole moments that oppose acentric order, diminishing EO performance. To address this, a better understanding of the relationship between molecular structure and bulk EO activity is required. In Chapter 2, the effects of functionalization of the benchmark chromophore YLD-124 on poling efficiency were studied. Substituents with different electronic nature and different sizes at the middle six-membered ring were explored. Attachment of a t-butylphenoxy group resulted in a 40% increase of the poling efficiency r33/Ep as well as significantly enhanced photostability. Unexpected optical properties of the functionalized chromophores in media with different polarities are explained in terms of electronic effects and aggregation. In Chapter 3, the synthesis of two chromophores with oblate shape is reported based on computational predictions that oblate spheroids with dipole moments formed short range linear stacks. These chromophores are potential candidates for application to a new type of nanophotonic device in which only several molecular layers of EO active material are required. An alternative approach for creating bulk acentricity upon crystallization is discussed in Chapter 4. A functionalization of two chromophores with acentric structure was performed in order to reduce the melting temperature of the parent materials. It was found that such a molecular arrangement is sensitive to the nature of the functionalization of the parent chromophores. Finally, the performance of novel polymerizable ionic liquids (PIL) as electrolytes for optoelectronic applications in polymeric light emitting electrochemical cells (LEC) is described in Chapter 5. The presented materials are organic salts and have allyl sulfonate as anion and trialkyl allyl/vinyl ammonium cation with varying length of alkyl groups; both anion and cation are capable of forming covalent bonds. LECs fabricated with these PILs demonstrated fixed junctions, improved film morphology and dramatically improved light output compared to the previously reported LEC with fixed junctions.