Photophysical properties of 1-(2-Hydroxy-5-Chloro-phenyl)-3, 5-dioxo-1H-thiazo-[3, 4-b] isoindole (HCHT) have been investigated thoroughly. Steady state and time resolved absorption and emission measurements in combination with theoretical calculation reveal that the synthesized molecule HCHT shows excited state thiolactim-thiolactum tautomerism through intramolecular hydrogen bonding between donor sulphur atom (-S-H) and acceptor nitrogen (N) atom. This is by far the first example where a sulfur atom is present as donor in an excited state proton transfer (ESIPT) process. Choice of sulfur atom in HCHT decelerates the irreversible ESIPT process compared to its oxygen atom donor analogue as evidenced from excited state lifetime experiments.

对1-（2-羟基-5-氯苯基）-3、5-二氧代-1H-噻唑-[3,4-b]异吲哚（HCHT）的光物理性质进行了彻底的研究。稳态和时间分辨吸收和发射测量结果以及理论计算表明，合成的HCHT分子通过供体硫原子（-SH）与受体氮（N）原子之间的氢键键合显示出激发态的硫代内酯-硫代托莱姆互变异构现象。这是迄今为止第一个例子，其中硫原子在激发态质子转移（ESIPT）过程中作为给体存在。从激发态寿命实验中可以看出，与氢氧供体类似物相比，HCHT中硫原子的选择降低了不可逆的ESIPT过程。