Insight into the electronic properties of organic semiconductors: Experimental measures from the isolated-molecule level to the solid-state device limit

Fundamental understanding of the electronic properties, and charge transfer mechanism of organic semiconductors and functionalized oligoacenes in particular, is of great importance for the design and fabrication of organic electronic devices. This work is devoted to the study of the electronic properties of organic semiconductors in the gas, solution, and solid phases, thus providing insights into the intra- and intermolecular electronic interactions of these materials from the isolated-molecule level to the solid-state device limit. The organic semiconductors investigated in this work are bis-triisopropylsilylethynyl-substituted (TIPS) anthracene, TIPS tetracene, TIPS pentacene, bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]-pentacene (TP-5), and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxadicyclopenta[b,m]pentacene (EtTP-5). This research is conducted on the basis of experimental and computational studies. The experimental analysis is based on the combination of closely-related gas-phase and solid-phase photoelectron spectroscopy measurements, along with electrochemical measurements in solution. The electronic structure quantum-mechanical computations are performed at the density functional theory level, and are in good agreement with experimental results.;First, an insight into the intramolecular electronic characteristics of TIPS anthracene, TIPS tetracene, and TIPS pentacene is presented (chapter 3). The main goal of this part of my research is to analyze the valence ionization energies, intramolecular (vibrational) reorganization energies of these molecules, and provide an understanding of the electronic effects associated with the substitution of oligoacenes by the triisopropylsilylethynyl groups and with the acene core size at the isolated-molecule level.;Next, the analysis of the electronic effect of the triisopropylsilylethynyl group is extended to the solution and solid phases. The study of this environment-dependent substitution effect is discussed by comparing the intra- and intermolecular electronic properties of pentacene and TIPS pentacene (chapter 4).;Further, the intermolecular electronic properties, such as ionization energies, charge-injection barriers, energy gaps, and polarization energies, of TIPS anthracene, TIPS tetracene, and TIPS pentacene (chapter 5) are discussed and compared with the intramolecular electronic properties presented earlier in order to gain the complete picture of electronic interactions in these molecules in all three phases (gas, solution, and solid).;Finally, the intra- and intermolecular electronic properties of TIPS, TP-5, and EtTP-5 pentacenes are presented in order to illustrate how different functional groups, when added to the pentacene core, affect the electronic structure and properties of pentacene in the gas, solution, and solid phases (chapter 6).;This dissertation reports important findings on the electronic properties of organic semiconductors and how these properties change between phases. The role of polarization effects on the electronic properties of these materials was demonstrated to be significant and strongly dependent on the molecular structure and electronic interactions at the isolated- (or single-) molecule level as well as on the molecular packing and electronic interactions in the solid state at the device limit.