激發態質子轉移與平面化分子之基礎研究與應用

Abstract

近來我們策略性合成一系列有關於激發態分子內質子轉移(ESIPT)以及激發態平面化化合物。首先在激發態分子內質子轉移系統中，我們合成一系列Amino (NRH)類型的激發態分子內質子轉移(ESIPT)化合物，我們簡單藉由修飾NRH的官能基的推拉電子效應，來探討其推拉電子效應對於化合物的光譜特性。其結果顯示藉由只修飾NRH的官能基的推拉電子效應，其放光特性以及光譜動力學性質會有相當大的改變。對照OH類型的激發態分子內質子轉移化合物，在不過多改變化合物的結構下，我們只改變NRH的官能基的推拉電子效應，便可以得到完全不同的性質，這些是OH類型的激發態分子內質子轉移化合物所無法達到的。此外我們也更進一步探討2-(2’-tosylaminophenyl)benzothiazole這分子受激發後的光物理現象。當激發2-(2’-tosylaminophenyl)benzothiazole分子時，會先進行分子內激發態質子轉移，接著進行順反異構化產生trans-tautomer。我們利用了nanosecond transient absorption (TA)、two-step laser-induced fluorescence (TSLIF)、pico-femtosecond photoluminescence up-conversion以及理論計算來證明整個光物理反應的機制。另一部分，在平面化分子體系下，我們實驗室發展了一系列有關N,N’-disubstituted-dihydrodibenzo[a,c]phenazines衍生物，這系列化合物在基態時呈現彎曲的構型，而在激發態會先產生馬鞍構型的分子間電子轉移中間態，接著進行平面化到最終平面構型，然而最終平面化構型會因為π電子非定域化(π-delocalization)放出紅光。因此為了進一步瞭解激發態平面化之結構變化，我們利用烷酯鏈將9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) 結構進行限制，有策略的合成一系列化合物DPAC-n (n=1~8)，其烷酯鏈不影響其衍生物的共軛性質。我們可以觀察到經由烷酯鏈長度的不同，可以有效的限制分子的激發態平面化行為，烷酯鏈長度與放光波長有著相對應的關係。更進一步的研究平面化系統，我們有策略的將DPAC結構中N上苯環接上不同數量的甲基藉此產生不同程度的立體障礙，形成一系列化合物Mx-My-DPAC (x = 0, 1 or 2, y = 1 or 2)，我們觀察到在基態時呈現的馬鞍構型會因立體障礙過大而直接產生平面構型。光譜動力學實驗以及理論計算可以解釋整個光物理反應的機制。

We have strategically designed and synthesized several new classes of excited-state proton transfer and planarization molecules In the cases of excited-state proton intramolecular proton transfer compounds, we have synthesized a series amino (NH)-type intramolecular hydrogen-bonding compounds via replacing one of the N–H hydrogen atoms by various substituents. It makes feasible comprehensive spectroscopy and dynamics studies of excited-state intramolecular proton transfer (ESIPT) as a function of N–H acidity. Another cases is excited-state planarization molecules, we deeply investigate the coupling of electronic processes with conformational motions, we exploit a tailored strategy to harness the excited-state planarization of 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) by halting the structural evolution via macrocyclization process, in which the para sites of 9,14-diphenyl are systematically enclosed by a dialkoxybenzene-alkyl-ester or -ether linkage with different chain lengths, imposing various degrees of constraint to impede the structural deformation. Accordingly, a series of DPAC-n (n = 1~8) derivatives were synthesized, in which n correlates with the alkyl length, such that the strength of the spatial constraint decreases as n increases. Furthermore we have thus strategically designed and synthesized a series of methylation structures based on DPAC as a core, where ortho sites of the 9,14-diphenyl moieties are chemically methylation by methyl group with different methylation , forming a series of new DPAC, Mx-My-DAPC (x = 0, 1 or 2, y = 1 or 2). Our aim was to impose various degrees of steric hindrance to distort the V-shape conformation of ground state structure so that we would be able to investigate the near planar structure in ground state. Comprehensive spectroscopic and dynamic studies, together with a computational approach, rationalized the associated excited-state structure responding to emission origin. For all of these cases, which are suitable for fundamental research and applications.