Bis(thio)carbohydrazone Luminogens with AIEE and ACQ Features and Their In Silico Investigations with SARS-CoV-2

Herein, we report two novel multidentate luminogen proligands bis(3,5-diiodosalicylidene) carbohydrazone (H₄L¹) and bis(3,5-diiodosalicylidene) thiocarbohydrazone (H₄L²), which are suitable candidates for biomedical applications. Though the thiocarbohydrazone H₄L² shows aggregation caused quenching (ACQ), the carbohydrazone H₄L¹ exhibits stronger fluorescence due to aggregation induced emission enhancement (AIEE). Molecular docking studies of H₄L¹ and H₄L² along with four similar (thio)carbohydrazones with the active sites of SARS-CoV-2 main protease 3CL^pro reveals that the thiocarbohydrazones, in general, are showing better propensity compared to their oxygen analogues. Both the thiocarbohydrazones and the carbohydrazones, however, exhibit better binding potential at the active sites than that of some of the repurposed drugs such as chloroquine, hydroxychloroquine, lopinavir, ritonavir, darunavir and remdesivir. Also, the carbohydrazone H₄L¹ can be a better bioprobe compared to H₄L² as the former is found to have better binding potential with SARS-CoV-2 spike glycoprotein along with AIEE feature.