Recent studies have highlighted the potential of organic room-temperature phosphorescence (RTP) materials for applications such as bioimaging, organic light-emitting diodes (OLEDs), dynamic light therapy, data encryption, and anti-counterfeiting [1]. Organic metal-free RTP compounds offer numerous advantages over inorganic or metal-based complexes and nanodot-based RTP systems, including lower cost and toxicity, extended emission lifetimes and tunable emission [2, 3]. The development of organic RTP materials was previously limited by their crystalline nature. Advances in amorphous polymer matrices and intermolecular interactions have overcome these challenges, enabling the development of programmable luminescent tags (PLTs) for flexible information storage [4, 5]. The long emission lifetime of RTP materials makes them unsuitable for OLED displays [6]. However, this characteristic allows their use in electronics-free thin-film information storage systems and wavelength-tracking sensors [7]. One type of such devices are emissive tags, which require long-lived luminescence and can be used for anticounterfeiting, labeling, and data exchange [8].
Phenoxathiin is still scarcely used as an electron donor. It was selected due to its distinctive structure, which includes oxygen and sulfur atoms [9]. This moiety is expected to enhance spin–orbit coupling, promoting intersystem crossing from the singlet to the triplet state, which is essential process for phosphorescence. Additionally, the presence of n orbitals within the phenoxathiin ring system may contribute to triplet state stabilization, while its rigid structure could minimize nonradiative decay, both of which are crucial for efficient RTP [10].
In this study, we report the synthesis, thermal, and photophysical properties, as well as the theoretical study of three new electron-accepting quinoxaline derivatives and three phenoxathiine containing donor–acceptor type compounds, as potential candidates for emissive tag fabrication. This project has received funding from the Research Council of Lithuania (LMTLT), agreement No S-MIP-23-50.