Thiazolo[5,4-d]Thiazole-Based Emerging Fluorescent Materials

Highly fluorescent molecular materials are of interest in various fields ranging from bioimaging to optoelectronic devices. Among many organic chromophores, the heterobicyclic thiazolo[5,4-d]thiazole (TzTz) chromophore has attracted attention for its planar, rigid molecular structure and high thermal and oxidative stability. The TzTz-based molecules and polymers have been of particular interest as active materials in optoelectronic devices (field-effect transistors and solar cells). However, fluorescent TzTz-based molecular systems have been of recent interest (about a decade or so). The ease of synthesis and tunable emission through subtle changes in molecular structure make TzTz chromophores ideal for applications across different fields. Here, we discuss the photoluminescence properties of TzTz derivatives in the condensed phase (dilute solution, assembled state, and solid-state) and their representative applications in ion sensing, electrochromic devices, organic light-emitting diodes (OLEDs), and cell imaging. Finally, the key photophysical properties of various TzTz derivatives are systematically catalogued, and their structure-property relationships are outlined.