兩性共軛奈米分子與其光捕捉微胞

Abstract

兩性奈米分子(MNP)在溶液中存在著各種不同的自組裝結構，本研究在奈米分子引入具光捕捉性質的基團藉此賦予MNP吸光特性並使分子成為具有兩親性的雅努斯粒子，藉此讓分子能隨溶液極性變化改變自組裝結構，調整吸光單元的排列模式。 本研究成功的合成了兩種不同的光捕捉兩性分子(LHA)，分別是具10個光捕捉單元2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)pyrrolo [3,4-c] pyrrole-1,4(2H,5H)-dione (DPP)、2個羧酸基的低極性分子LHA1，以及具有2個DPP單元、10個羧酸基的高極性分子LHA2，並使用NMR光譜確定了LHA的結構，在分子的自組裝方面，運用動態光散射光譜與原子力顯微鏡的結果架構出分子的自組裝結果，發現隨溶液極性改變(water/THF=1/1 to hexane/THF =1/1)影響了自組裝結構及吸光單元的排列模式。 本研究透過紫外光/可見光吸收光譜儀測量薄膜態的LHA1和LHA2分子，確認分子Eg 約為1.93 eV，是吸收綠光的吸光單元。以循環伏安儀測定分子的最高占據軌域能階(EHOMO)及最低未占軌域能階(ELUMO)，得到分子的EHOMO及ELUMO分別為-5.46 eV 及-3.53 eV (LHA1)，以及-5.35 eV及-3.41 eV (LHA2)，證實了LHA的能階滿足光催化水裂解反應的需求。在光催化水裂解實驗中，雖然LHA1和LHA2在單獨存在時並沒有顯示出顯著的產氫效果，但是在LHA與二氧化鈦的混合樣品中透過LHA吸收可見光的能力補足了二氧化鈦在可見光波段貧弱的吸收，進而成功的提升了二氧化鈦的產氫效率。

Amphiphilic molecular nanoparticles (MNP) exhibited versatile self-assembled micellar morphologies in solutions. Adding light harvesting(LH) units to the MNPs turns the conventional amphiphilic MNPs into LH MNPs, and the interplay between the solvent polarity and the amphiphilicity of the LH MNPs provides the possibility to adjust the arrangment of the conjugated units in solutions. In this work, two green light-harvesting amphiphiles (LHA), LHA1 and LHA2, were synthesized. The more hydrophobic LHA1 contains 10 hydrophobic LH units-2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole -1,4(2H,5H)-dione (DPP) and 2 hydrophilic -COOH groups, while the more hydrophilic LHA2 contains 2 hydrophobic DPP units and 10 hydrophilic -COOH groups. NMR spectra confirmed the chemical identity of the LHAs. Their micellar morphologies were investigated through dynamic light scattering (DLS) and atomic force microscope(AFM). The changes of the solvent polarity (water/THF=1/1 to hexane/THF=1/1) results in the changes of the micellar structure and the spatial arrangements of the LH units. LHA1 and LHA2 are green LH molecule, since their Eg are ~ 1.93 eV as determined from the thin-film UV-Vis (UV-Vis) absorption spetra. The cyclic voltammetry (CV) results indicated that the highest occupied energy level (EHOMO), and the lowest unoccupied energy level (ELUMO) are -5.46 eV and -3.53 eV for LHA1; and -5.35 eV, -3.41 eV for LHA2. These energy levels are suitable for the photocatalytic water splitting reaction. In the hydrogen generation experiments, although the LHAs didn't show much effect on their own, they enhanced the hydrogen-generation efficiency of TiO2 by compensating the poor absorption of TiO2 in visible light region.