雙胺基取代剛性二苯乙烯系統之光物理性質及扭轉運動之探討

Abstract

在我們實驗室過去的工作中，我們在含有間位 (meta-) 胺基的剛性二苯乙烯衍生物中觀察到了高強度的螢光，其螢光量子產率在正己烷中高達0.73，並且在順式結構中能保有非常強的螢光，是順式二苯乙烯系列分子非常罕見的。而在鄰位 (ortho-) 胺基取代之剛性二苯乙烯衍生物中，我們可以透過胺基上甲基的訊號來分析分子在基態下的螺旋反轉運動，亦是較少可以探討螺旋反轉運動的例子，而由於光異構化反應而使此化合物之螢光被焠熄。 在此工作中，我們將間位胺基引入於鄰位胺基取代剛性二苯乙烯之另一側苯環，設計出含鄰位-間位之omDASS分子，欲使其具有螢光的表現，並探討其在光物理性質與扭轉運動之間的關係，而我們同時合成了雙間位 (mmDASS) 之分子，探討雙胺基系統之光物理現象。在 (E)-mmDASS分子在正己烷中觀察到了較單間位胺基取代化合物來得弱的放光，僅有0.42的螢光量子產率，然而在高極性之乙腈中，則呈現相反的趨勢，擁有高達0.79的螢光量子產率，是由於該化合物中，溶劑效應在1t*及1p*兩能階所造成的效應不同所致。而對於化合物 (E)-omDASS，我們成功地使其有些微螢光表現，並在動力學NMR的實驗中，反式異構物的訊號變化可以用來分析基態下的剛性二苯乙烯之螺旋反轉運動，而順式異構物則可以看到胺基旋轉的運動。透過光異構化量子產率的測量，發現其光異構化無法有效地受到間位胺基的抑制，仍有0.49的異構化量子產率，其原因為鄰位胺基會造成分子有較為扭曲的結構，因此助長了光異構化的反應發生。

In our recent work, we observed strong fluorescence quantum yield up to 0.73 in hexane for stiff-stilbene derivatives bearing meta-amino group. And its cis isomer also had high fluorescence quantum yields in both hexane and acetonitrile. To our best knowledge, it’s the first example of cis-stilbene series that exhibited strong fluorescence. Moreover, ortho-amino substituted stiff-stilbene analyzed helical inversion in the ground state. It is also a rare example of a single small molecule that analyzes helical inversion. Unfortunately, the fluorescence was quenched because of fast photoisomerization. In this work, we synthesized omDASS by introducing a meta-amino group on the other side of phenyl ring of ortho-amino substituted stiff-stilbene. We predicted that the meta-amino group could enhance the fluorescence intensity by lowering the photoisomerization quantum yield. Thus we could discuss the fluorescence behavior and torsional motion in this system. Moreover, we synthesized bis-amino derivatives bearing meta-meta (mm-) amino groups on opposite sites to discuss its photophysical properties. We observed that the fluorescence intensity was weaker than the mono m-amino substituted one in the non-polar solvent. The fluorescence quantum yield of (E)-mmDASS was only 0.42 in hexane. However, the fluorescence quantum yield is up to 0.79 in acetonitrile. As for (E)-omDASS, we can also analyze the ground state motions in VT-NMR experiments. The fluorescence of (E)-omDASS is successfully turned on although the performance is not very well as expected because the photoisomerization of (E)-omDASS could not be inhibited efficiently due to the twisted conformation.