Klymchenko Andrey S, Demchenko Alexander P
TUBITAK Research Institute for Genetic Engineering and Biotechnology, 41470, Gebze-Kocaeli, Turkey.
J Am Chem Soc. 2002 Oct 16;124(41):12372-9. doi: 10.1021/ja027669l.
Internal Stark effect (or internal electrochromy) consists of the shift of light absorption and emission bands under the influence of electric field produced by proximal charges. In the studies of 3-hydroxyflavone (3HF) derivatives exhibiting the excited-state intramolecular proton transfer (ESIPT), we describe a new phenomenon - a very strong internal electrochromic modulation of this reaction. Fluorescence spectra of 3HF derivatives with charged groups attached to the chromophore from the opposite sides without pi-electronic conjugation, N-[(4'-diethylamino)-3-hydroxy-6-flavonyl]methyl-N,N-dimethyloctylammonium bromide and 4-[4-[4'-(3-hydroxyflavonyl)]piperazino]-1-(3-sulfopropyl)pyridinium, were compared with those of their neutral analogues in a series of representative solvents. The introduction of the proximal charge results in shifts of absorption spectrum and of both normal (N) and tautomer (T) emission bands, which correspond to initial and phototautomer states of the ESIPT reaction. The observed shifts are in accordance with the Stark effect theory. The direction of the shift depends on the position of the proximal charge with respect to the chromophore. The magnitude of the shift depends strongly on the solvent dielectric constant and on screening or unscreening produced by addition of the hydrophobic salts. In all of these cases, the spectral shifts are accompanied by extremely strong variations of relative intensities of N and T emission bands. This signifies a strong influence of internal electric field on the ESIPT reaction, which produces a dramatic change of emission color. Thus, the coupling of the initial electrochromic sensory signal with the ESIPT reaction allows for the breaking of the limit in magnitude of response inherent to common electrochromic dyes. This suggests a new principle of designing the ultrasensitive electrochromic two-wavelength fluorescence sensors and probes for analytical chemistry, macromolecular science, and cellular biology.
内斯塔克效应（或内电致变色）是指在近端电荷产生的电场影响下，光吸收和发射带的位移。在对表现出激发态分子内质子转移（ESIPT）的3-羟基黄酮（3HF）衍生物的研究中，我们描述了一种新现象——该反应的一种非常强烈的内电致变色调制。在一系列代表性溶剂中，将发色团两侧带有电荷基团且无π电子共轭的3HF衍生物，即N-[(4'-二乙氨基)-3-羟基-6-黄酮基]甲基-N,N-二甲基辛基溴化铵和4-[4-[4'-(3-羟基黄酮基)]哌嗪基]-1-(3-磺丙基)吡啶鎓，与其中性类似物的荧光光谱进行了比较。近端电荷的引入导致吸收光谱以及对应于ESIPT反应初始态和光互变异构体态的正常（N）发射带和互变异构体（T）发射带都发生位移。观察到的位移符合斯塔克效应理论。位移方向取决于近端电荷相对于发色团的位置。位移幅度强烈取决于溶剂介电常数以及添加疏水盐所产生的屏蔽或去屏蔽作用。在所有这些情况下，光谱位移都伴随着N和T发射带相对强度的极大变化。这表明内电场对ESIPT反应有很强的影响，导致发射颜色发生显著变化。因此，初始电致变色传感信号与ESIPT反应的耦合打破了普通电致变色染料固有响应幅度的限制。这为分析化学、高分子科学和细胞生物学设计超灵敏电致变色双波长荧光传感器和探针提出了一种新原理。
