Non-benzenoid Aromatic Systems: Design, Synthesis, Properties, And Applications

Due to remarkable advantages of organic materials, such as facile synthesis and easy structural modification, small-size, large store, fast response etc., the study of organic materials has become one of the most important research area arising from multidiscipline subjects (Chemistry, Physics, and Material Science) in the 21^st century. In this dissertation, design, synthesis, characterization, and subsequently optoelectronic application of organic compounds with non-benzenoid substructure are systematically presented and discussed.First, dibenzocycloheptatrienylidene-ended non-benzenoid systems and their analogous are synthesized and characterized through the Wittig-Horner, the Suzuki, and the Sonogashira reactions. After taking full investigation of their optical properties in solutions, in nanoparticles, in neat thin films, in doped PMMA, in "glass" solutions, and in powders, enhanced emissions are observed for all of them except one compound. Fluorescence quantum yields in solutions can be stimulated by π-conjugation extension, molecular planarization and rigidization. Enhanced emissions arising from solids may attribute to the cooperation of restricted intramolecular rotations, molecular planarization and rigidization, and the prevented intermolecular interactions in solid states. The magnitude times of quantum yields (Φ_nano/Φ_sol) arising from solution to nano-suspension linearly increases with an increment of differences of energy band gaps (ΔE) between solution and film. Excellent linear correlation (correlation factor r = 0.996) is obtained for all these compounds with varied centers, ends, and side chains. The bigger ΔE a molecule has, the stronger enhanced emission the solid states would be. This linear correlation should exist inherently in organic light emitting materials. Therefore, the establishment of this structure-property relationship would be valuable for researchers to design and optimizeorganic materials with better performance.Second, "green emission tail" (500-600 nm) from fluorene-based oligomers or polymers limits their applications in organic light emitting diodes (OLEDs). Two possible reasons for the "green bands" emission were proposed in the literature. One was the emission from keto defects of the oligo- or poly-fluorenes confirmed experimentally and the other was the emission from face-to-face (//-type) aggregates of the oligo- or poly-fluorenes in solid states. Nevertheless, there are neither the direct nor strong evidences to prove the existence of the "green bands" emission coming from //-type aggregates. A series of 2', 7'-diarylspiro(cyclopropane-l,9'-fluorene)s are thereby synthesized and characterized for focusing the reason of the "green bands" emission. At the meanwhile, the variations of the optical properties of these molecules in the solid states depend on the stacking modes of these compounds with different substituents, which are shown by the crystallographic analysis. CH/rc hydrogen bonds act as the driving forces instead of 71-71 intermolecular interactions between adjacent fluorenes in these cases, although the spirocyclopropane moiety as the smallest dialkyl group is introduced at the C-9 position of the fluorene. Therefore, the crystallographic analysis gives the direct evidence for absence of face to face intermolecular interaction between the fluorenes, that is, the H-type aggregates. In order to reveal the realistic reason for the "green bands" emission, the fluorescence spectra of the films annealed in N2 or in air were recorded. Broad green emission tails were only observed for the films annealed in air. As a result, the postulation that "green" emission tail comes from the //-type aggregates is inconceivable, which might be caused by fluorenone defects generated during handling the materials in air, or by reaction with residual oxygen in the course of photophysical experimentation.Third, a series of 9-(cycloheptatrienylidene)fluorene derivatives as typical non-benzenoid 7t-conjugated systems were synthesized in good yields through the Suzuki or the Sonogashira cross-coupling reactions with full characterization. On the basis of investigation of their acid-triggered UV-vis and fluorescence properties, principle sensors triggered by acid were established. From 9-(cycloheptatrienylidene) fluorene (9-CHF) as an single-mode (absorbant) sensor in high acidic environment, to 2,7-diaryl-9-CHF all astwo-modes (absorbant and fluorescence) sensors in milder acidic environment, to 2,7-bis(/?-dimethylaminophenyl)-9-CHF not only as multi-mode (absorbant, fluorescence, and their wavelength-ratio) sensors in wider pH range, but also as a probe for detecting N-alkylpyridium cation, the applications of these derivatives as sensors are well extended. Moreover, the possible mechanisms for sensing processes are postulated and examined by taking full investigation of their optical properties and theoretical calculation. Further, on the basis of their sensing properties, YES, NOT, and NOR logic gates are established based on these molecules. By integrating different functions, such as emission intensity, absorbance, ratios of emission intensities, and ratios of absorbance as output signals, a two-input/multioutput function has been successfully established.In conclusion, this dissertation presents synthesis, characterization, and applications of new organic compounds with non-benzenoid substructure. On the basis of the systematically investigation of these synthesized compounds, a certain structure-property relationship of fluorescence is well established which is hitherto a mystery for all researchers in photochemistry and photophysics area. Moreover, their potential applications, utilized as sensors, logic gates, light emitting materials, are discussed in detail. We hope these results, with plentifulness and creation, will merit the research on Chemistry, Physics, and Material Science.