Photoinduced trans-to-cis Isomerization of Cyclocurcumin

Abstract

The photophysical properties of cyclocurcumin in various solvents are studied for the first time to shed light on the nonradiative processes of the parent compound, curcumin, which has a range of medicinal properties. Steady-state fluorescence and fluorescence-excitation spectra of cyclocurcumin in polar aprotic solvents are strongly dependent on excitation (λ(ex)) and emission (λ(em)) wavelength, respectively. The fluorescence quantum yield also depends on λ(ex) and increases with the viscosity of the medium. Time-resolved studies show nonexponential fluorescence decay in all solvents studied. The two fluorescence decay components of cyclocurcumin in alcohols exhibit a strong dependence on viscosity and temperature. NMR spectroscopy indicates that cyclocurcumin is entirely in the trans form with respect to the C6-C7 double bond in methanol, chloroform, and acetone. It is suggested that at least two conformational isomers about another single bond (C5-C6 or C7-C1″ or both) and that trans-to-cis isomerization about the C6-C7 double bond of these isomers provide the most likely means of rationalizing the steady-state spectra and the nonradiative decay mechanisms in both protic and aprotic polar solvents.

Curcumin‐free turmeric exhibits anti‐inflammatory and anticancer activities: Identification of novel components of turmeric

“…Cyclocurcumin was also found to inhibit the proliferation of human breast cancer MCF‐7 cells . More recently light‐induced trans ‐to‐ cis isomerization of cyclocurcumin was reported .…”

Dynamics and Mechanism of Intercalation/De-Intercalation of Rhodamine B during the Polymorphic Transformation of the CdAl Layered Double Hydroxide to the Brucite-like Cadmium Hydroxide

“…This phenomenon was explained by Drexhage 35 , who studied the lifetime dependence of the xanthene dyes on the amino group's flexibility. Thus, upon excitation and due to the rotation ability along the C-N bonds, these dyes show a distortion in their excited state to form a twisted intramolecular charge transfer state (TICT) [36][37][38] . This charge transfer results in a non-radiative decay leading to smaller values of the fluorescence lifetime 33 .…”

Kinetics of intercalation of fluorescent probes in magnesium–aluminium layered double hydroxide within a multiscale reaction–diffusion framework

“…Theoretical explanations of this phenomenon were given by Drexhage [28], who studied the dependence of the lifetime of RhB on the amino group's flexibility. Thus, upon excitation and due to the ability of rotation along the C-N bond, this probe displays a distortion in its excited state to form a twisted intra-molecular charge transfer (TICT) state [29][30][31]. This internal rotation results in a non-radiative decay; consequently, fewer lifetime values are exhibited [32].…”