| Summary: | 碩士 === 國立臺灣師範大學 === 化學研究所 === 91 === Abstract
The triaryethene synthesis adopt helical shapes（ie helicenes）, due to the steric overlap of symmetrical upper-part (dibenzosuberane) and the unsymmetrical lower part(β-naphtholflavone,α-tetralone etc). The chirality of these helicenes are defined as P or M for right- or left-hand helical handness.We synthesized a series of MOM (Methoxy-methyl) -substituted helicenes, and designed different structure and conjugation of lower part to evaluate these effects on their photophysical properties and photochemistry behavior.
By irradiation, the central double bond of the helicenes loose its’ double bond character and exhibits diradical character. It has been documented that the relaxation of the excited state to the ground state procceds through two pathways. First, planarization around the diradical unit with increasing ring strainand with concomitant rotation leading to the perpendecular excited state enroute to another photostationary ground state. Therefore, upon receiving irradiation energy, the helicenes consume the energy by double-bond photoisomerization. In this thesis, we have synthesized (10R,11R,P) MOM-7-Br helicene as the target optical-switching material. It was irradiated in toluene at 310nm,the opposite, pseudoenantiomeric helicene(10R,11R, M)isomer was furnished almost exclusively. The switching process was found reversible. The original (10R,11R,P) isomer may be enriched by irradiating (10R,11R,M)-isomer at 254nmas evidenced by HPLC and CD analyses. As mentioned above, we can use this reversible progress to apply the helicenes as LC-optical switch. Secon, an alternative way to release energy was by fluorescent emission.By selection of a different kinds of lower part, we can tune the irradiation wavelength and MOM-substituted upper part help to increase the energy barrier to photoisomerization and thus increase the fluorescence quantum yield. We used these photophysical properties to apply in organic light emitting materials.
Based on photochemical behaviors of chiral MOM-substituted hlicene. We added 1 equivalent V-complex to bind bothmethoxymethye oxygens. We can effect reversal of photoisomerization selectivities.
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