Bhattacharyya Arghyadeep, Das Akash, Guchhait Nikhil
Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata, 700009, India.
Phys Chem Chem Phys. 2023 Nov 29;25(46):31702-31713. doi: 10.1039/d3cp03603k.
A novel Schiff base 4-bromo-2-(()-(()-(1-(naphthalen-2-yl)ethylidene)hydrazono)methyl)phenol (BNHMP) was synthesized and characterized by NMR, ESI-MS, FTIR and single crystal X-ray diffraction studies. In the solution phase, BNHMP shows prominent emission from the keto-form, a consequence of excited state intramolecular proton transfer (ESIPT). The quantum yield and excited state lifetime decrease in polar solvent THF compared to relatively non-polar solvent DCM. Interestingly, in aqueous solution (pH 7.0), the quantum yield along with the excited state lifetime undergoes tremendous increment. Dynamic light scattering experiments and FESEM reveal the formation of aggregates in water as reflected by the increased hydrodynamic radius of BNHMP in water. Hence, aqueous phase studies revealed BNHMP to be an AIE active probe. On the other hand, BNHMP shows huge emission intensity in the solid state. Interestingly, the emission decay behavior of BNHMP changes upon excitation, as BNHMP shows very broad absorption in the solid state. Upon excitation at 360 nm, a triexponential decay pattern is found, which changes to a biexponential one upon excitation at 450 nm. Meticulous analysis of the fluorescence lifetimes led to the assignment of J and H aggregates coexisting in the solid state with the former dominating the photodynamics. A judicious comparison of the lifetime behavior in the solid state to that in water leads to the conclusion that BNHMP undergoes AIE by the formation of J and H aggregates to an equal extent, a phenomenon starkly different from the solid-state scenario. The current results hold significance as this is among a few reports where such comprehensive spectrodynamic dissection has been performed for an ESIPT-AIE active Schiff base in solution as well as in the solid phase, thereby giving a holistic vision of the nature and fate of aggregation occurring in such azine based systems and subsequently advancing the understanding of such systems in terms of their photo behavior.
合成了一种新型席夫碱4-溴-2-(((()-((1-(萘-2-基)亚乙基)肼基)甲基)苯酚(BNHMP)，并通过核磁共振、电喷雾电离质谱、傅里叶变换红外光谱和单晶X射线衍射研究对其进行了表征。在溶液相中，BNHMP显示出酮式结构的显著发射，这是激发态分子内质子转移(ESIPT)的结果。与相对非极性溶剂二氯甲烷相比，在极性溶剂四氢呋喃中量子产率和激发态寿命降低。有趣的是，在水溶液(pH 7.0)中，量子产率和激发态寿命都有显著增加。动态光散射实验和场发射扫描电子显微镜显示，水中形成了聚集体，这反映在BNHMP在水中增加的流体力学半径上。因此，水相研究表明BNHMP是一种聚集诱导发光(AIE)活性探针。另一方面，BNHMP在固态下显示出巨大的发射强度。有趣的是，BNHMP的发射衰减行为在激发时会发生变化，因为BNHMP在固态下显示出非常宽的吸收。在360 nm激发时，发现了三指数衰减模式，在450 nm激发时变为双指数衰减模式。对荧光寿命的细致分析导致确定在固态中存在J和H聚集体，前者主导光动力学。将固态下的寿命行为与水中的寿命行为进行明智的比较得出结论，BNHMP通过形成J和H聚集体在同等程度上发生AIE，这一现象与固态情况截然不同。目前的结果具有重要意义，因为这是少数几篇对溶液和固相中的ESIPT-AIE活性席夫碱进行如此全面的光谱动力学剖析的报道之一，从而全面了解了这种基于嗪的体系中聚集的性质和命运，并随后在光行为方面推进了对这类体系的理解。
