Indian Institute of Science Education and Research, Bhopal , Bhopal By-Pass Road , Bhauri, Bhopal 462066 , Madhya Pradesh , India.
ACS Appl Mater Interfaces. 2018 Dec 26;10(51):44696-44705. doi: 10.1021/acsami.8b14215. Epub 2018 Dec 17.
The excited-state intramolecular proton transfer (ESIPT)-based molecular probes have drawn significant attention owing to their environment-sensitive fluorescence properties, large Stokes shift, and emerged as building blocks for the development of molecular sensors and switches. However, most of the ESIPT-based fluorophores exhibit weak emission in the solid state limiting the scope of real-time applications. Addressing such issues, herein, we presented a C symmetric-like molecular architecture employing a simple one-step Schiff base condensation between triaminoguanidinium chloride and 3,5-di- tert-butyl-2-hydroxybenzaldehyde (TGHB). The temperature-dependent fluorescence studies including at 77 K indicated the strong emission from the keto tautomer compared to that of the enol tautomer. The facile ESIPT in TGHB in the solid-state led to a remarkable enhancement of fluorescence quantum yield of 1600 times compared to that of the solution (λ = 545 nm) by restricting the intramolecular rotation and subsequently suppressing the nonradiative deactivation. The excited-state processes were further elucidated through time-resolved fluorescence measurements. TGHB exhibited turn on-off fluorescence upon exposure to acid/base vapor in the form of a powder as well as a transparent, free-standing thin film. A rewritable and erasable fluorescent platform was demonstrated using TGHB as molecular ink, which offers a potential testbed for performing "write-erase-write" cycles multiple times. In addition, TGHB, possessing multiple binding sites (O and N donors) involving the central core of the triaminoguanidinium cation displayed selective turn-on fluorescence with Zn. The structure-property relationship revealed in the present study provides insight into the development of novel cost-effective multifunctional materials, which are promising for stimuli-responsive molecular switches.
基于激发态分子内质子转移（ESIPT）的分子探针由于其环境敏感的荧光性质、大斯托克斯位移以及在分子传感器和开关的发展中作为构建块而受到了极大的关注。然而，大多数基于 ESIPT 的荧光团在固态下表现出较弱的发射，限制了实时应用的范围。针对这些问题，本文提出了一种 C 对称类似的分子结构，采用三氨基胍盐酸盐和 3,5-二叔丁基-2-羟基苯甲醛（TGHB）之间的简单一步席夫碱缩合反应。包括在 77 K 下的温度依赖性荧光研究表明，与烯醇互变异构体相比，酮互变异构体具有较强的发射。在固态下，TGHB 中易于发生 ESIPT，通过限制分子内旋转，从而抑制非辐射失活，导致荧光量子产率与溶液相比提高了 1600 倍（λ = 545nm）。通过时间分辨荧光测量进一步阐明了激发态过程。TGHB 在暴露于酸/碱蒸气时以粉末和透明、独立的薄膜形式表现出开-关荧光。使用 TGHB 作为分子墨水展示了可重写和可擦除的荧光平台，这为进行多次“写-擦-写”循环提供了一个潜在的测试平台。此外，TGHB 具有多个结合位点（O 和 N 供体），涉及三氨基胍阳离子的中心核心，显示出与 Zn 的选择性开-关荧光。本研究中的结构-性质关系为开发新型经济高效的多功能材料提供了深入的了解，这些材料有望成为对刺激响应分子开关。
