Synthesis, Structural Characterization and In Silico ADME Analysis of a Rhodamine B-Based Schiff Base

A new rhodamine B-based Schiff base (RSB) derivative was successfully synthesized via condensation of rhodamine B hydrazide with 5-bromo-2-hydroxybenzaldehyde and characterized using FT-IR spectroscopy, NMR, single-crystal X-ray diffraction, photophysical studies and in silico ADME analysis. FT-IR data confirmed the formation of the azomethine (C=N) functionality together with the preservation of the spirolactam ring structure. Single-crystal X-ray analysis revealed that the compound crystallizes in the triclinic crystal system with the centrosymmetric space group P-1. Structural analysis confirmed the closed spirolactam form and showed the presence of an intramolecular O–H···N hydrogen bond stabilizing the molecular conformation, while weak intermolecular C–H···O interactions contribute to the supramolecular architecture. Photophysical investigations in DMF solution demonstrated absorption bands at 307 and 348 nm, attributed to π→π* and n→π* transitions, respectively. Upon excitation at 498 nm, the compound exhibited green fluorescence emission centered at 513 nm. The observed optical behavior originates from the extended conjugated xanthene–hydrazone framework. Furthermore, the physicochemical and pharmacokinetic properties of the compound were evaluated using the SwissADME platform. The results indicated high lipophilicity, low gastrointestinal absorption, absence of blood–brain barrier permeability, and favorable intracellular retention characteristics. Although the compound does not fully satisfy conventional drug-likeness criteria due to its high molecular weight and lipophilicity, its strong fluorescence properties and predicted membrane affinity suggest that the synthesized RSB derivative may represent as a promising candidate for fluorescent imaging and sensing applications.