Photophysical properties of substituted intramolecularly hydrogen bonded compounds: A combined experimental and theoretical study

Curcumin is the main constituent of curry. In its ground state it shows chemo-preventive, chemo-therapeutic and anti-inflammatory effects. For its immunostimulating action it has been considered for the development of drugs suitable for treating AIDS and cystic fibrosis. Further biological action is induced in curcumin by photoactivation: in suitable environmental conditions electronically excited curcumin can act as a singlet oxygen generator. Moreover, cytotoxicity is enhanced by light exposure and antibacterial effects are photosensitized. This work is aimed to understand the photobiological action of curcumin by elucidating the deactivation mechanisms of its first excited singlet state. In particular we find evidence of the role of tautomerization in the excited state by measuring fluorescence lifetimes and quantum yields for such compound dissolved in solvents of different polarity and H-bonding capability. Degradation quantum yield and singlet oxygen generation efficiency were also measured in acetonitrile and methanol. The results emphasize the strong dependence of the deactivation processes from the environment. The deactivation phenomenology can be fully explained by postulating intramolecular proton transfer in thecisenol conformer to be the leading non-radiative deactivation pathway.

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“…(3) The ESIPT rate is higher the tighter is the intramolecular H-bond between the enol and the keto moiety [18][19][20][21].…”

Section: Resultsmentioning

confidence: 99%

“…This excited-state intramolecular proton transfer (ESIPT) becomes even faster in the presence of the intramolecular H-bond in Fig. 1C [18][19][20][21], as demonstrated for molecules having chemical structures similar to that of curcumin. Rates as high as 10 11 s −1 were reported [19].…”

Section: Discussionmentioning

confidence: 97%

Role of H-bond formation in the photoreactivity of curcumin

et al. 2008

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“…For example, Mitra and Mukherjee 33 studied the ESIPT photophysical properties of 4-methyl-2,6-diformylphenol and 4-methyl-2,6-diacetylphenol using time-resolved fluorescence spectroscopy and ab initio calculations. This work found that the ultrafast ESIPT process was followed by a rapid intramolecular vibrational relaxation (IVR) with a time constant of few picoseconds before fluorescence emission occurred from their keto tautomer on the excited-state potential energy surface . Cho et al investigated the relaxation processes of the excited-state intramolecular reverse proton transfer (r-ESIPT) in the excited triplet state of 1-hydroxyanthraquinone by using transient Raman spectroscopy and ab initio calculations .…”

Section: Introductionmentioning

confidence: 99%

“…Since Weller discovered the excited-state intramolecular proton-transfer (ESIPT) reaction of methyl salicylate (MS), ESIPT reactions have been observed to play an important role in many chemical and biological systems. − ESIPT reactions have also found many important applications in laser materials, − in information storage devices and optical switching, − in hard-scintillation counters, and as polymer photostabilizers. , A number of experimental and theoretical studies have investigated the types of ESIPT reactions − and the subsequent complicated reaction mechanisms − that may take place for a range of molecular systems. Many aspects of the reaction mechanisms of ESIPT processes in a variety of chemical and biological species have been elucidated by various time-resolved spectroscopic measurements and quantum mechanical studies.…”

Section: Introductionmentioning

confidence: 99%

Resonance Raman Intensity Analysis of the Excited-State Proton-Transfer Dynamics of 2-Hydroxybenzaldehyde in the Charge-Transfer/Proton-Transfer Absorption Band

et al. 2007

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Resonance Raman spectra were obtained for 2-hydroxybenzaldehyde (OHBA) in cyclohexane solution with excitation wavelengths in resonance with the first charge-transfer/proton-transfer (CT/PT) band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion predominantly along the nominal C=CH in-plane bend+ring deformation modes (nu9, nu10, nu14, nu16, nu18, nu19, nu20, nu26, nu30, nu31, and nu35) accompanied by a smaller amount of motion along the nominal C=O stretch mode (nu7), the nominal C=C-C(=O) in-plane bend modes (nu33 and nu37), and the nominal ring C-O-H in-plane bend modes (nu9 and nu14). A preliminary resonance Raman intensity analysis was done, and these results for the OHBA molecule were compared to results previously reported for the 2-hydroxyacetophenone (OHAP) molecule. Several proton-transfer tautomers in the ground and excited states were predicted from the results of B3LYP/cc-PVTZ, UB3LYP/cc-PVTZ, and CASSCF/cc-PVDZ level of theory computations. The differences and similarities between the CT/PT band resonance Raman spectra and the vibrational reorganizational energies for the OHBA molecule relative to those for the OHAP molecule are briefly discussed.

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“…4,5 The formation of an intramolecular hydrogen bond (IHB) in a molecule, such as 4X substituted 2-hydroxybenzaldehydes (4X-2OHBz), plays a crucial role in the determination of its physicochemical behavior. [6][7][8] Although theoretical investigations of the parent molecule have been conducted, no investigations of substituted salicyladehydes have been reported. [9][10][11] With the aim of contributing to clarify the influence of solvents and substituents on the conformational equilibria and the IHB of 4X-2OHBz, in this work we carry out a structural study of these compounds in hydroxylic solvents by means of a B3LYP/ 6-31G(d) method (Becke hybrid three-parameter nonlocal exchange functional combined with the Lee-Yang-Parr dynamic correlation functional) 12,13 that makes use of the SCIPCM (self-consistent isodensity polarizable continuum model) model.…”

Section: Introductionmentioning

confidence: 99%