2-(4′-Diethylamino-2′-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine (DHP) has two mutually independent reaction paths, excited state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT). To uncover the effect of acidity and basicity on the reaction coordinate, the molecule was studied in the complete range, from higher acidity H₀ (Hammett’s acidity scale) – 10 to high basicity H_ (Yagil’s basicity scale) 16.4 using UV–visible and fluorescence techniques, along with quantum mechanical calculations. The molecule possesses complicated prototropic equibrium with multiple cations and anions in addition to the neutral species. The emission maximum changes from 375 nm to 560 nm depending on the acidity and basicity of the solution. All the prototropic species were identified experimentally and comprehensively entrenched with the help of computational calculations. The methoxy derivative was studied to substantiate the assignment. The neutral species predominantly emits the tautomer emission. Upon deprotonation one red shifted emission and one blue shifted emission are observed due to formation of two different monoanions. Even at higher basicity H_ 16.2, the dianion formation was not completed. Three monocations are formed, one emits normal emission, one emits tautomer emission and the third one emits highly Stokes shifted ICT emission. Among the dications, one dication undergoes biprotonic phototautomersism to produce tautomer of other dication in the excited state. Unlike dianion, the trication formation is completed at higher acidity H₀ − 10.

2-(4'-Diethylamino-2'-hydroxyphenyl)-1 H -imidazo-[4,5-b]pyridine (DHP) 有两条相互独立的反应路径，激发态分子内质子转移 (ESIPT) 和扭曲分子内电荷转移(TICT)。为了揭示酸度和碱度对反应坐标的影响，在整个范围内研究了分子，从较高酸度 H ₀（哈米特酸度标度） – 10 到高碱度 H_（Yagil 碱度标度） 16.4 使用紫外-可见光和荧光技术，以及量子力学计算。除了中性物质外，该分子还具有多个阳离子和阴离子的复杂质子平衡。根据溶液的酸度和碱度，发射最大值从 375 nm 变为 560 nm。在计算计算的帮助下，通过实验和全面地确定了所有原热带物种。研究甲氧基衍生物以证实该分配。中性物质主要发射互变异构体发射。在去质子化时，由于形成了两种不同的单阴离子，观察到一种红移发射和一种蓝移发射。即使在更高的碱度 H_ 16.2，二价阴离子的形成没有完成。形成三个单阳离子，一个发射正常发射，一个发射互变异构体发射，第三个发射高度斯托克斯位移的 ICT 发射。在这些指示中，一个指示经历双质子光互变异构以产生处于激发态的其他指示的互变异构体。与二价阴离子不同，三阳离子的形成是在较高的酸度 H 下完成的₀  - 10。