Related Experiment Video
Updated: Aug 6, 2026
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Positional isomerism-driven solvatochromism and excited-state behavior in ortho- and para-hydroxy bromobenzylidene
Yadigar Gülseven Sıdır1, Halil Berber2, İsa Sıdır1
1Bitlis Eren University, Faculty of Sciences and Letters, Department of Physics, 13000 Bitlis, Türkiye. ygsidir@beu.edu.tr.
Abstract:
This study presents a comprehensive investigation of how hydroxyl positional isomerism governs the solvatochromic response and excited-state behavior of bromobenzylidene Schiff base derivatives. Two structurally related isomers, SB-oOH and SB-pOH, were synthesized and systematically analyzed using combined spectroscopic and quantum chemical approaches. The results reveal a striking contrast in photophysical behavior arising solely from the substituent position. SB-oOH exhibits weak solvent-dependent spectral shifts, attributed to intramolecular O-H⋯N hydrogen bonding that restricts π-electron delocalization and stabilizes a localized excitation (LE) state. In contrast, SB-pOH displays pronounced positive solvatochromism, large Stokes shifts, and strong solvent sensitivity, consistent with increased polarizability and stronger light-matter interaction, whereas SB-oOH maintains a more rigid and less responsive electronic structure. Quantitative solvatochromic analysis using linear solvation energy relationship (LSER) models demonstrates that SB-oOH is primarily influenced by nonspecific dielectric interactions, while SB-pOH is strongly governed by both solvent polarity and hydrogen-bonding effects. Theoretical calculations based on density functional theory (DFT) and time-dependent DFT (TD-DFT) support these findings, revealing enhanced HOMO-LUMO separation, a reduced energy gap, and increased electronic delocalization in the para-substituted system. Furthermore, optical band gap and refractive index analyses confirm that the enhanced ICT characteristic of SB-pOH, as supported by the combined experimental and theoretical results, is consistent with increased polarizability and stronger light-matter interactions, whereas SB-oOH maintains a more rigid and less responsive electronic structure. Thus, this study demonstrates that subtle structural variation through hydroxyl positional isomerism can induce profound changes in electronic structure and excited-state dynamics. These findings provide a clear structure-property relationship and offer a rational strategy for designing Schiff base-based functional materials with tunable optoelectronic properties. This study highlights positional isomerism as an effective molecular design tool for controlling excited-state processes.
Related Concept Videos
02:52Stereoisomerism
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
01:37NMR Spectroscopy of Benzene Derivatives
01:14Directing Effect of Substituents: ortho–para-Directing Groups
01:11Nomenclature of Aromatic Compounds with Multiple Substituents
For disubstituted benzene derivatives, with two groups attached to the benzene ring, three constitutional isomers are possible. For example, consider dimethyl benzene, often called xylene, where the second methyl group can be substituted at the second, third, or fourth carbon. The relative position of the substituents is represented by prefixes ortho, meta, or...
00:58¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...