Premium
Effect of Solvent on the Excited‐state Photophysical Properties of Curcumin ¶
Author(s) -
Khopde Sujata M.,
Indira Priyadarsini K.,
Palit* Dipak K.,
Mukherjee Tulsi
Publication year - 2000
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2000)0720625eosote2.0.co2
Subject(s) - photochemistry , flash photolysis , chemistry , quantum yield , excited state , absorption (acoustics) , fluorescence , ultrafast laser spectroscopy , quenching (fluorescence) , absorption spectroscopy , materials science , spectroscopy , kinetics , atomic physics , reaction rate constant , physics , quantum mechanics , composite material
Photophysical properties of curcumin, 1,7‐bis‐(4‐hydroxy‐3‐methoxy phenyl)‐1,6‐heptadiene‐2,5‐dione, a pigment found in the rhizomes of Curcuma longa (turmeric) have been studied in different kinds of organic solvent and also in Triton X‐100 aqueous micellar media using time‐resolved fluorescence and transient absorption techniques having pico and nanosecond time resolution, in addition to steady‐state absorption and fluorescence spectroscopic techniques. Steady‐state absorption and fluorescence characteristics of curcumin have been found to be sensitive to the solvent characteristics. Large change (Δμ= 6.1 Debye) in dipole moments due to photoexcitation to the excited singlet state (S 1 ) indicates strong intramolecular charge transfer character of the latter. Curcumin is a weakly fluorescent molecule and the fluorescence decay properties in most of the solvents could be fitted well to a double‐exponential decay function. The shorter component having lifetime in the range 50–350 ps and percent contribution of amplitude more than 90% in different solvents may be assigned to the enol form, whereas the longer component, having lifetime in the range 500–1180 ps with less than 10% contribution may be assigned to the di‐keto form of curcumin. Our nuclear magnetic resonance study in CDCl 3 and dimethyl sulfoxide‐D 6 also supports the fact that the enol form is present in the solution by more than about 95% in these solvents. Excited singlet (S 1 ) and triplet (T 1 ) absorption spectrum and decay kinetics have been characterized by pico and nanosecond laser flash photolysis. Quantum yield of the triplet is low (φ T ≤ 0.12). Both the fluorescence and triplet quantum yields being low (φ f +φ T < 0.18), the photophysics of curcumin is dominated by the energy relaxation mechanism via the internal conversion process.