Photochromic spiroindolium iodide derivatives; synthesis, Molecular geometry DFT assessment and UV–vis photophysical investigation

Abstract

Facile synthesis of photochromic spiroindolium iodide derivatives 3a, 3b and 5 via nucleophilic substitution reaction of 1,2,3,3-tetramethyl-3H-indolium iodide with different o‑hydroxy benzaldehyde or naphthaldehyde derivatives. The structure of the synthesized compounds was confirmed by different spectral analyses such as FT-IR,¹H NMR, ¹³C NMR spectra and elemental analysis. The photochromic properties of synthesized compounds were measured via UV–vis photophysical measurements. The photochromism was investigated using UV-spectrophotometer before and after exposure to direct sunlight. Overall, compounds 3a, 3b and 5 shows a new peak at range 500–600 nm in visible region to confirm that the energy absorbed was sufficient to change them to their open structure forms. Then, we present density functional theory (DFT) calculations on the synthesized photochromic compounds 3a, 3b and 5 and their isomeric open forms, aiming to explore their potential thermodynamic stability, molecular geometry, frontier molecular orbitals energy gap investigation as well as their molecular electrostatic potential mapping. By analyzing the influence of UV–vis energy on molecular interactions and electronic transitions, we aim to elucidate the relationship between molecular structure and photochromic behavior.