- 學位論文
激發態分子內質子轉移耦合熱活化延遲熒光新興材料的概念進展
Conceptual Advance for Emerging Materials Exhibiting Excited-state Intramolecular Proton Transfer Coupled Thermally Activated Delayed Fluorescence
摘要
激發態分子內電荷轉移(ESICT)耦合質子轉移(ESIPT)已被廣泛研究，其中可以通過微調常態構形(normal form)及互變異構型態(tautomeric form)之間的相對能量以在激發態達到平衡。在本研究中，我們策略性地設計了ESICT/ESIPT分子，其常態構形表現出扭曲型(twisted type)激發態電荷轉移(CT)，因此在電子供體和受體之間具有良好的空間分離，使其在最低單重態(S1(CT))和三重態(T1(CT))之間可達到較小的能隙(ΔES-T)，從而實現它們在室溫下的熱可逆性。該類型分子的電子受體具有分子內氫鍵，在S1(CT)激發時電荷轉移誘導發生ESIPT，其中常態構形(S1(CT))和質子轉移互變異構型態(S'1(PT))之間的能量可通過更換取代基微調以達到平衡。最終預期結果是能在S1(CT)、T1(CT)和S'1(PT)狀態之間建立熱可逆性。因而TADF可由T1(CT)經反向系統間跨越至預平衡的S1(CT)和S'1(PT)能階下形成。該概念的證明是通過合成新的ESICT/ESIPT耦合化合物2-hydroxy-4-(10H-phenoxazin-10-phenylmethanone (OH-PXZ-PM)。其中，放光光譜量測結果顯示，OH-PXZ-PM在環己烷溶液及摻雜薄膜中皆可經ESIPT同時呈現常態構形（530 nm）及質子轉移互變異構體（625 nm）放光帶，且兩種放光帶都顯示出顯著的TADF，這是我們首次觀察到單分子單元中產生雙TADF現象，該研究實現ESIPT/TADF耦合性質極有助於新興材料發展。
並列摘要
Excited-state intramolecular charge transfer (ESICT) coupled proton transfer (ESIPT) has been widely studied, where the relative energy between normal and tautomeric forms can be fine-tuned to reach equilibrium in the excited state. In this study we strategically design the ESICT/ESIPT molecules where the normal species exhibits a twisted type excited state charge transfer (CT) and hence possesses a decent spatial separation between electron donor and acceptor. This makes possible a small energy gap, △ES-T, for the normal species between the lowest lying singlet (S1(CT)) and triplet (T1(CT)) states, achieving their thermal reversibility at room temperature. The electron acceptor is endowed with intramolecular hydrogen bond. Upon S1(CT) excitation, the CT induced ESIPT takes place, where energetics between (S1(CT)) and proton-transfer tautomer (S’1(PT)) states can be fine-tuned to reach equilibrium. The net result is to establish a thermal reversibility among S1 (CT), T1 (CT) and S’1(PT) states. TADF can thus be generated in both S1(CT) and S’1(PT) states modulated by T1(CT). The proof of concept is provided by the synthesis of a new ESICT/ESIPT coupled compound 2-hydroxy-4-(10H-phenoxazin-10-phenylmethanone (OH-PXZ-PM). OH-PXZ-PM undergoes ESIPT and exhibits both normal (530 nm) and proton-transfer tautomer (625 nm) emission bands in cyclohexane and dope film, where both emissions reveal prominent TADF, generating dual TADF in a single molecular unit for the first time, making a conceptual advance for emerging materials to attain ESIPT/TADF properties.