Syntheses of New Polycyclic Aromatics via Double Oxidative Photocyclization or Oxidative Heck Cyclization
Date Issued
2014
Date
2014
Author(s)
Li, Wan-Cin
Abstract
π-Conjugated polycyclic aromatic compounds have the great potential to act as superior semiconductors due to their unique structure and property, making them good candidates for the applications in optoelectronic devices such as organic field effect transistors (OFETs), organic light-emitting diodes (OLEDs), and organic photovoltaic cells. Recently, polycyclic aromatic compounds have received great attention, numerous synthetic strategies were used to construct novel structures with planarity and π-conjugation. One of the classic synthetic methodologies for large aromatic systems is the oxidative photocyclization. In addition, the well-explored palladium(Ⅱ)-mediated oxidative Heck reaction is also profitable.
In this thesis, we report the synthesis of novel thiophene-fused polycyclic aromatics from tailor-made precursors, utilizing either a double oxidative photocyclization reaction under UV-light irradiation in the presence of iodine; or palladium(Ⅱ) acetate-mediated oxidative Heck cyclization. Various aromatic rings including pyridine, benzene, and naphthalene were incorporated as the central linkage, giving various bent arenedithiophenes. Structural identifications of heteroacenes 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. We found that there are bathochromic effects in absorption as well as emission spectra of cyclized products compared to those of precursors. Simultaneously the band gaps narrows after cyclization, while the different bending mode of angular, spiral, and kinked products leads them to have distinctive spectral and electrochemical properties, as well as crystal packing pattern, depending on the effect of bending mode of aromatic skeleton to aromaticity and coplanarity of bent arenedithiophenes. This gives us opportunity for tailoring the HOMO/LUMO energy levels of the cyclized products via varying the fusing form of polycyclic aromatic compounds. The characteristic heterodimer formation in crystal phase of helical compounds also furnishes the potential for self-assembly application, where aggregation by pure nonplanar π-π stacking is expected. In addition, ring closure products via oxidative Heck cyclization shows significant regioselectivity comparing to that from oxidative photocyclization. Product selectivity of photocyclization mainly depends on the stability of dihydro intermediates which is further oxidized to cyclized products, while that of oxidative Heck cyclization is the combination of C-H bond activity and steric effect.
Subjects
光環化
多環芳香族
赫克反應
SDGs
Type
thesis
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