1.香豆素衍生物之合成及其在有機電致發光二極體及熱致變色材料物理性質之探討2.激發態電荷/質子轉移競爭平衡反應與分子偶極矩的關係
1.Synthesis and Physical Property Studies of Coumarin Derivatives on OLED and Thermochromic Materials 2.Tuning Excited–State Charge/ Proton Transfer Coupled Reaction via the Dipolar Functionality
Date Issued
2005
Date
2005
Author(s)
Huang, Chien-Huang
DOI
zh-TW
Abstract
One of the objectives of this dissertation is to develop coumarin-based derivatives suitable for the application of OLED. Accordingly, three series of coumarin-based derivatives bearing diarylamino groups have been synthesized and their photophysical and electrical properties are evaluated. Their structures are showed in Fig.1 and they should emit red, green, and blue fluorescenct light, respectively. To address the structure-photophysical properties relationship, substituents with e--donating (i.e. methyl (-Me), (-OMe)) or e--withdrawing groups (i.e. cyano (-CN), trifluoromethyl (-CF3), chloro (-Cl)) are introduced at either para- or meta-positions. These substituents can tune the conjugation length, fluorescent wavelength, quantum yield, as well as oxidative potentials (ionization potential) of the molecules. As a result, the e--withdrawing groups exert effects on the raising ionization potential of e- donor and the energy level of TICT state. Thus, ICT radiation pathway becomes the dominant one. Good linear correlations were evidenced between substituents’ electronic effects and ionization potentials/quantum yields. Furthermore, these coumarin-based derivatives exhibit amorphous behaviors and hole-transporting materials, which are critical for effective emitting properties in the application of OLED.
Development of novel reversible thermochromic materials is also the aim of my research endeavors. The coumarin-based molecules and the mechanism of reversible thermochromic behaviors are shown in Fig. 2. The bulky ortho-brominated aryl groups are implanted to create nonplanarity around amino center. Thus, the effective conjugation length to the protonation site is shortened and the energy gap between neutral and protonated forms is narrowed. The protonation can only occur at the nitrogen atom of the benzothiazole and the temperature variation disturbs the equilibrium between the neutral and monocation and the reverible thermochromic effect can thus be achieved. As evidenced by VT-UV-vis spectroscopy, unique “yellow-to-orange” colorimetric transitions of 3Br in various solvents were observed in the presence of 6N HCl (1 μL). In CH2Cl2 or CHCl3, the color of solution gradually changed from orange to yellow between r.t. and 0 oC The backward “yellow-to-orange” transition did occur when the stimulus is removed afterwards from the system. In CH3CN, it requires heating to 80 oC to observe the color changes. Both of VT-Fluorescence and VT-1H NMR spectra confirm the acid-base equilibrium in the heating-and-cooling cycles. The system showed excellent thermo-stability.
Different e--donors and e--acceptors are incorporated at the phenyl ring of the benzothiazole to decipher the relationship between basicity of nitrogen atom and thermochromic phenomenon. In collaboration with Dr. Ito Chao et al. at Academic Sinica, different bridges with distinct conjugation features and lengths are evaluated for their roles on the thermochromic phenomenon.
The last part of the dissertation is to study excited state intramolecular charge transfer (ESICT) and proton transfer (ESIPT) coupled reactions exemplified by a series of 3-hydroxyflavone derivatives. The difference in solvent polarity environment between excited state intramolecular charge transfer (ESICT) and proton transfer (ESIPT) states leads to a remarkable ESICT/ ESIPT coupled reaction. In polar, aprotic solvents, in contrast to a unique PT tautomer emission observed in 3-hydroxyflavone (3HF), dual emissions are resolved, consisting of ESICT and ESIPT bands. Based on the chemical synthetic design, we demonstrate an approach to modify the positions of functional groups and e-donating (or withdrawing) abilities, which can fine-tune the ESICT/ ESIPT coupled reaction via the dipolar orientation of the molecular framework. Dialkylamine, which is an e-donor, was introduced at the C(4’) or C(7) positions in 3HF resulting in similar ESICT/ESIPT dual emission. Even the net dipole moment, the orientation of which is affected by the CT effect, is expected different. Dialkylamine attached at both C(4’) and C(7) positions in 3HF, of which the net dipole moment may be associated with the interplay between two charge-transfer systems, displayed different photo behaviors. As a consequence, switching the dipolar property of the CT state can greatly tune the ESICT/ESIPT coupling behavior among them. This makes feasible further rational design of ESICT/ESIPT systems by altering the net dipolar vector.
Subjects
有機電致發光二極體
熱致變色
香豆素
OLED
Thermochromic
Coumarin
Type
thesis
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