The role of the oxime group in the excited state deactivation processes of indirubin

Abstract

The introduction of an oxime group into indirubin derivatives, including INROx, MINROx, and 6-BrINROx, and its impact on the spectral and photophysical properties of INR was investigated using a combination...

Excited-State Intramolecular Proton Transfer toward Conical Intersections in Indigo, Epindolidione, and Indirubin

“…For indigo, CI with a planar molecular structure was also located in previous quantum chemical calculations. 23,25,28,32 To the best of our knowledge, the planar CI of indirubin has been located for the first time in the present work, although Nobre et al 54 proposed a CI of indirubin which exhibits the twisting of the central C� C bond based on TDDFT calculations.…”

“…The TDDFT emission energies of indigo and indirubin calculated in the present work are similar to those in previous TDDFT studies. 25,26,54 For the Min(KE) structure of indigo, the emission energies calculated with the TDDFT and XMS-CASPT2 methods are substantially higher than the emission energy of conformer Y (∼1.0 eV) calculated with the ADC(2) method, 27,32 probably because of the different reference wave function: Kohn−Sham, CASSCF, and Hartree−Fock for TDDFT, XMS-CASPT2, and ADC(2), respectively.…”

“…The π and π* orbitals exhibit bonding and antibonding character at the central C�C bond, respectively, as reported in previous calculations. 23,50,54 For the XMS-CASPT2(10,10) calculation of indirubin, however, the π orbital deviates from the central C�C bond in the reference CASSCF wave function. The irreducible representation of the S 1 (ππ*) state is B u for indigo and epindolidione while A′ for indirubin.…”

“…18 For indirubin, in contrast, it has been shown that the quantum yield and lifetime of fluorescence are exceptionally small as in the case of indigo. 19,54 In dimethylformamide (DMF) solution, the fluorescence quantum yield and lifetime are reported as 0.0003 and 14 ps, respectively, for indirubin, while 0.0023 and 135 ps for indigo. 19,54 Theoretical investigations of photochemical reactions are necessary to understand the origin of the differences and similarities in the photophysics and photochemistry of the three isomers indigo, epindolidione, and indirubin at the molecular level.…”

Keto-enol tautomerism in the development of new drugs

“…Indirubin itself has 26 possible E/Z isomers and tautomers, some of which are more stable than others (Alkorta et al, 2020). A recent publication reports a very rapid keto-enol tautomerization (<1 ps) when an oxime group is introduced in an indirubin derivative, promoting an excited-state proton transfer process and additionally improving the photostability of the compound compared to the precursor (Nobre et al, 2024).…”