Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Dr. Uwe H. F. Bunz, Committee Chair ; Dr. Laren M. Tolbert, Committee Member ; Dr. Joseph Perry, Committee Member ; Dr. David M. Collard, Committee Member ; Dr. Anselm C. Griffin, Committee Member.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

Two new series of organic soluble indigoids 7-7-dialkoxyindigoids (4a, 4b) and 4,4-dibromo-7,7-dialkoxyindigoids (5a, 5b) (alkoxy = n-butoxy and n-octyloxy) have been synthesized starting from the inexpensive 3-hydroxybenzaldehyde for OFET applications. The indigoids were soluble in common organic solvents such as chloroform, dichloromethane, toluene, ethyl acetate and ethers. The enhanced solubility was suggested to be a lack of intermolecular hydrogen-bonds as confirmed by single crystal X-ray diffraction analyses. It was found that intramolecular hydrogen-bonds in indigoids were crucial to the exhibition of field-effect in OFETs, while intermolecular hydrogen-bonds only caused insolubility of the indigoids. Compared to the pristine insoluble indigo (LUMO = -3.55 eV and Eg = 1.91 eV), the soluble indigoids containing electron donating alkoxy side chains at the indigoid 7 and 7 positions were shown to have LUMO decreased by -0.13 to -0.26 eV as well as a lower bandgap energy from Eg = 1.66 to 1.94 eV. A bottom-gate-top-contact OFET employing polystyrene as the dielectric layer was used to demonstrate the field-effect properties. The indigoid 4,4-dibromo-7,7-dioctyloxyindigoid (5b) was found to exhibit the highest electron mobility at 2.20 ₉ 10-5 cm2V-1s-1. In addition, 4,4-dibromo-7,7-dioctyloxyindigoids (5) can be further derivatized by organometallic catalyzed aryl-aryl coupling reactions to create functional organic electronic materials.

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This diploma thesis describes study and onward synthesis of advanced organic structures with potential application in the field of organic electronics and, in particular, molecular photoswitches. In the theoretical part of the thesis are closely described most commonly used conventional molecular photoswitches with special attention to the influence of the structural modifications on properties and applications of the given derivatives. Next passage is dedicated to study of donor-acceptor systems, as fundamental building blocks for synthesis of advanced derivatives. The possibilities of derivatization with a goal of improving the physicochemical properties of these compounds are also discussed. In the final chapter are proposed modern synthetic methods for preparation of novel materials for organic electronics. This section is connected with an experimental part, where are designed and consequently synthesised 4 novel imine derivatives with dodecyl and adamantyl-ethyl side chain.

Traps are ubiquitously present in semiconductors. Their presence results in ineffective charge transport and thus limited the device performance. For organic semiconductors, traps can present intrinsically via structural disorder or extrinsically during synthesis or device fabrication. A thorough understanding of traps is important to optimize the device performance and material design. This thesis employs two trap measurement techniques, photothermal deflection spectroscopy (PDS) and thermal admittance spectroscopy (TAS), to investigate the trap density in the materials. The subgap optical absorptions of several high performance bulk-heterojunction (BHJ) systems for organic solar cells have been studied by PDS. The charge transfer (CT) states are, in particular, looked into detail. CT states are intermediate bound electron-hole pairs at the donor/acceptor (D/A) interface of an organic solar cell. The dynamics and energetics of CT states are crucial to free charge generation and recombination processes. With the help of PDS and external quantum efficiency (EQE) measurements, the CT states the delocalized CT states (hot) from the localized CT states (cold) are observed and differentiated directly. It is discovered that the localized CT states are more pronounced when the acceptor concentration reaches its percolation limit. As the acceptor concentration reaches its optimized composition, the intensity of these CT states is significantly reduced due to the reduced recombination. Using the CT energies measured from PDS, the open-circuit voltage losses from the BHJs are determined. Besides PDS, thermal admittance spectroscopy (TAS) is employed as an alternative method to measure the trap densities. TAS measures the frequency dependent capacitance response of a semiconductor under a small ac signal excitation. This technique is useful to measure the trap depth and trap density of a semiconductor. The defect profiles in two classes of materials are investigated, they are perovskite compounds and an organic hole transporter with an intentional dopant. The trap density are determined by TAS is compared with that obtained by PDS.

This thesis presents studies of organic semiconductor lasers, including their operation when pumped by a light-emitting diode (LED), and their application as explosive sensors. The photophysics and amplified spontaneous emission (ASE) of star-shaped oligofluorene truxene molecules were investigated. These materials exhibit high gain and low optical loss in thin-film waveguides. Low ASE thresholds were achieved with the truxene T3 and T4. Second-order distributed feedback (DFB) lasers were fabricated, with pump threshold intensities below 0.5 kW/cm² and broad tunability of the emission. DFB lasers were demonstrated with a novel polymer BBEHP-PPV, pumped by a pulsed commercial InGaN LED. The laser emission occurred at 533 nm for peak drive current above 15 A. The output beams and pulse-dynamics of the lasers were investigated for the first time, along with a 'double-threshold' phenomenon that was observed in this long-pulse pumping regime. BBEHP-PPV lasers based on various types of diffractive resonators were also fabricated by UV nanoimprint-lithography (NIL). By optimising the resonator design and the fabrication, and the pump-beam geometry, polymer laser thresholds of ~60 W/cm², the lowest recorded for NIL lasers, were demonstrated, enabling them to be pumped by pulsed commercial LEDs and custom micro-LED arrays. One promising application of organic lasers is in explosive sensing. A polymer of intrinsic microporosity (PIM-1) was used to detect nitroaromatic vapours. Rapid detection of dinitrobenzene (DNB) of low vapour pressure was achieved by monitoring the photoluminescence and laser emission during exposure. In addition, a CMOS time-resolved fluorescence lifetime microsystem with a commercial green-emitting copolymer was used as a novel, portable sensor to detect DNB vapour. An InGaN LED pumped BBEHP-PPV laser was also used as a miniature sensor to detect 10 ppb of DNB. These highly sensitive hybrid sensors could be used in humanitarian demining, complementing existing technologies leading to improvement in the detection of hazardous objects.