Synthesis, Photophysical Characterization, and DFT Analysis of (E)-1-(4-aminophenyl)-3-(1-benzyl-pyrrol-2-yl) Prop-2-en-1-one, a Novel Aminochalcone that can be Used as a Fluorescent Probe for Protein Labeling.

A novel aminochalcone, (E)-1-(4-aminophenyl)-3-(1-benzyl-pyrrol-2-yl)prop-2-en-1-one, was synthesized via Claisen-Schmidt condensation and fully characterized using FT-IR, NMR spectroscopy, and GC-MS analysis. The compound's photophysical properties were studied using UV-Vis absorption and fluorescence spectroscopy in solvents of varying polarity. These studies revealed marked solvatochromic and solvatofluorochromic behavior, which is consistent with an intramolecular charge-transfer process. In polar media, the compound exhibited strong bathochromic shifts and a solvent-dependent fluorescence quantum yield of 0.012 ± 0.001, 0.061 ± 0.004 and 0.098 ± 0.007 in methanol, acetonitrile and chloroform, respectively. Ground- and excited-state dipole moments calculated from Lippert-Mataga and Bakhshiev correlations confirmed an increase upon excitation. DFT calculations at the B3LYP/6-311G(d, p) level corroborated the experimental results, indicating a minimal HOMO-LUMO gap and a planar conjugated system exhibiting donor-acceptor properties. Furthermore, the compound effectively functioned as a fluorescent probe for protein labeling under mildly acidic conditions (pH = 4.0) via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-mediated coupling, yielding consistent emission across proteins of different molecular weights. Altogether, these results indicate that this new aminochalcone possesses structural tunability, stable fluorescence, and bioconjugation capability, positioning it as a promising scaffold for fluorescence-based biochemical applications.