Syntheses, Structures, and Property Studies of Polycyclic Heteroarenes via Oxidative Photocyclization
Date Issued
2011
Date
2011
Author(s)
Yang, Shang-Jung
Abstract
Polycyclic π-conjugated organic compounds have thrived over the past few decades because of their strong potential as superior semiconductors and versatile application in electronic devices, such as organic field-effect transistors (OTETs), organic light-emitting diodes (OLEDs), and photovoltaic cell. One of the classic synthetic methodologies for large aromatic systems is the oxidative photocyclization. In this regard, numerous successful cases based on using diarylethene or 2-vinylbiphenyl derivatives as the precursors have been reported. In this thesis, we accomplished an alternative synthetic route of novel thiophene-fused polycyclic structures utilizing vinyl groups substituted thiophene derivatives as the starting materials. Accordingly, we have prepared a new series of C2- and C3-symmetric polycyclic heteroacenes by UV-light irradiation in the presence of iodine. Delicate molecular designs conducted on the starting materials make specific sites available for subsequent ring closures. Structural identifications of heteroacenes and their precursors are based on X-ray crystal diffraction analysis. The photophysical and electrochemical properties are characterized by studying their UV-Vis/photoluminescence (PL) and cyclic voltammetry (CV), respectively. Various aromatic rings including thiophene, 2,1,3-benzothiadiazole, and quinoxaline were incorporated as the central linkage, giving the opportunities for tailoring the HOMO/LUMO energy levels of the cyclized products. Interestingly, we found that different symmetry of molecules gives rise to distinct characters. There is a bathochromic effect in absorption as well as emission spectra of C3-symmetric compounds featuring with lower LUMO energy levels after ring closure. On the other hand, in the case of C2-symmetric system, the absorption and emission bands blue-shift, where the HOMO energy levels of cyclized compounds become much lower, whereas the LUMO energy level remains intact or slightly shifts to higher levels. In addition, we reported the solvent effects of photocyclization reaction and the photochromism-like property of C3 symmetric compound in this thesis.
Subjects
photocyclization
thiophene
photoreaction
heteroacene
polycyclic heteroarene
SDGs
Type
thesis
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