氟取代基效應對蒽-五苯荑衍生物之晶體結構及光致機械力放光變色之探討

Abstract

刺激響應材料是具有智能行為的材料，它能夠感知外界環境如外力、溫度、蒸氣、光等刺激而產生可被偵測的變化量。以光作為刺激源的響應材料近年來備受關注。本實驗室近年發展了不同碳鏈長度修飾的五苯荑，並以蒽作為螢光團的化合物P(Cn)，其於固態下展現同質多晶形性，分別為Y型、G型、B型。在光刺激下Y型與G型皆會進行二聚合，並展現放光變色的現象；B型則沒有二聚合的發生。二聚合與晶格剛硬度的交互作用造成光機械應力，進而影響蒽蒽間的交互作用，使得晶體展現獨特的光色變化。此為文獻中前所未見的光致機械力放光變色 (photomechanofluorochromism, PMFC) 現象。 本論文根據本實驗室近年研究成果及文獻資料，分別在五苯荑的長碳鏈上或蒽上進行氟取代，設計出化合物P(F)、An(F)、An(F)P(F)。前兩種化合物展現同質多晶形性，為G型及B型，而後者化合物只具有G型。在光刺激下，三種化合物晶體呈現不盡相同的光色變化，其中P(F)的G型晶體形狀更隨著光刺激而有顯著變化，經紫外光照射後晶體彎離光源。對此進行晶體結構分析，來探討氟取代基在分子排列及晶體放光顏色上、形狀上所造成的影響。再進一步結合晶體結構、光物理參數、二聚合程度等數據，探討PMFC和光機械效應的現象，並進而提出在光刺激下晶體變化機制。以期氟取代基對固態刺激響應材料性質的影響對日後科學家在分子設計上有所幫助。

Stimuli-responsive materials are materials with intelligent behavior. They can sense the external stimuli such as external force, temperature, steam, light, and so on, by producing detectable signals. Among those stimuli, light have received much attention in recent years. In our previous work, we have synthesized P(Cn), a monosubstituted anthracene as the chromophore with pentiptycene moiety modified with different length of alkyl chain. They exhibited polymorphism in the solid state, including yellow fluorescence (Y form), green fluorescence (G form) and blue fluorescence (B form). Under light irradiation, the Y form and the G form underwent dimerization along with the change of fluorescence color while B form was unreactive. The fluorescence color change resulted from the interaction between dimerization and lattice rigidity. The interaction caused photomechanical stress, which in turn affected the interaction between anthracene moieties, making the crystal exhibit unique fluorescence color change. We named this “photomechanofluorochromism”, abbreviated as PMFC. Based on our research and the previous observation of others’ research, we designed P(F), An(F), An(F)P(F) derivatives by fluorine substitution on the alkyl chain or on anthracene. P(F) and An(F) exhibited polymorphism including a G form and a B form. An(F)P(F) only exhibited a G form. Under UV light irradiation, their crystals showed different fluorescence color change, and the shape of the P(F) G form crystal deformed significantly. The P(F) G form crystal bent away from the light source after irradiation. Therefore, the crystal structure analysis was carried out to investigate the effects of the fluoro substituents on the molecular arrangement, the fluorescence color, and the crystal shape. We further combined the data of crystal structure, photophysical parameters, and degree of dimerization to propose a mechanism to explain the change of crystal under light irradiation. By studying on these derivatives, we hope that the fluoro-substituent effect on the properties of solid-state fluorescent materials can pave the way for the molecular design toward better understanding of the PMFC properties.