Photophysics of 3-hydroxyflavone in supercritical CO2: a probe to study the microenvironment of SCF

Abstract

The excitation of 3-hydroxyflavone (3HF) to its second excited singlet state (S 2 ) gives rise to dual fluorescence in supercritical carbon dioxide. The ultraviolet fluorescence originated from the S 2 state of 3HF is well separated from the green emission emanating from the tautomeric form, produced via the excited state intramolecular proton transfer. The relative intensity of the S 2 to the tautomer fluorescence (S 2 /T) has been studied as a function of pressure and temperature. It is shown that this ratio reflects the microheterogeneity of the supercritical CO 2 , and confirms the value of fluorometric probes in disclosing the microscopic properties of supercritical fluids.

Dramatic Pressure-Dependent Quenching Effects in Supercritical CO2 Assessed by the Fluorescence of 4‘-Dimethylamino-3-hydroxyflavone. Thermodynamic versus Kinetics Control of Excited-State Intramolecular Proton Transfer

“…DMA3HF in scCO 2 gives rise to dual fluorescence when photoexcited to the S 1 state, as observed before in liquid solutions 18 and in phospholipid membranes for this dye 11 and its derivatives. ,,− , It is pertinent to point out here that, unlike in common fluid solvents, in scCO 2 this probe also gives rise to fluorescence from the S 2 state. This observation is very similar to our previous observation with the parent compound 3HF in scCO 2 , , and with some other similar compounds in the vapor phase as shown previously by Nagaoka et al In the present article, we focus only on the S 1 emissions from the normal and the tautomeric species.…”

“…The extension of the π-electronic system and the introduction of electron-donor substituents lead to an enhanced sensitivity of the positions of these bands (λ N* , λ T* ) and, especially, their intensity ratios ( I N* / I T* ), to the properties of molecular environment. The strong influence that the microenvironment exerts on the spectroscopic parameters of this family of compounds motivated their widespread use as fluorescent probes for various purposes. ,− …”

“…The strong influence that the microenvironment exerts on the spectroscopic parameters of this family of compounds motivated their widespread use as fluorescent probes for various purposes. 11,[13][14][15][16][17] The present work focuses on the fluorescence properties of 4′-dimethylamino-3-hydroxyflavone (DMA3HF), a remarkably sensitive fluorophore, as a function of the pressure and temperature of scCO 2 . The evaluation of polarity and H-bonding in scCO 2 is facilitated by the large amount of experimental data available for DMA3HF and for the closely related 4′-diethylamino-3-hydroxyflavone (DEA3HF) fluorescent probe in different liquid solvents.…”

Fluorescence from the second excited singlet state of 3-hydroxyflavone in supercritical CO2

“…In the present Letter, we report, for the first time, a fluorescence from the second excited singlet state of 3HF in supercritical CO 2 environment. In the following Letter, we have exploited the relative intensity of the S 2 to the tautomer fluorescence (S 2 /T) to probe the microenvironments available in the supercritical fluids [24].…”

Proton Transfer Reactions in the Excited Electronic State

“…S 0 conversion. Recent publications on 3HF behaviour in supercritical CO 2 demonstrate this possibility [76]. Observations of anti-Kasha fluorescence are reported for different dyes.…”