New Insights into the Dual Fluorescence of Methyl Salicylate: Effects of Intermolecular Hydrogen Bonding and Solvation

Zhou, Panwang; Hoffmann, Mark R.; Han, Keli; He, Guo‐Zhong

doi:10.1021/jp501881j

Cited by 172 publications

(136 citation statements)

References 43 publications

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“…Letter Because the previous FDIRS study 24 showed no sign of II, there could be some reservations about the newly proposed mechanism 22 for the dual fluorescence of MS in protic solvents. If II does not exist in sufficient abundance, the ESIPT process cannot occur to produce sufficient intensity in the 440 nm band.…”

Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 97%

Rotational Spectra of Two Hydrogen-Bonded Methyl Salicylate Monohydrates: Relative Stability and Tunneling Motions

Ghosh

Thomas

Huang

et al. 2015

J. Phys. Chem. Lett.

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The mechanism for the dual fluorescence of methyl salicylate (MS) is a longstanding research topic. Two distinctly different hydrogen-bonded MS−water complexes, one with the carbonyl O and the other with the hydroxy O serving as the hydrogen-bond acceptor, were detected using chirped pulse and cavity-based Fourier transform microwave spectroscopy and found to be of comparable stability. This observation provides direct experimental evidence for the previously undetected hydroxy O-bonded isomer, supporting the recently proposed new mechanism for the dual fluorescence of MS in protic solvents. An interesting interplay between the methyl internal rotation and water tunneling motions was also investigated. The existence of an unconventional O···H−C hydrogen-bond was verified using the atoms-in-molecules theory. Thorough searches for the elusive ketoA, a higher energy form of MS, were unsuccessful. This result supports recent theoretical reports that only one MS species exists in the ground state.

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Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 97%

Rotational Spectra of Two Hydrogen-Bonded Methyl Salicylate Monohydrates: Relative Stability and Tunneling Motions

Ghosh

Thomas

Huang

et al. 2015

J. Phys. Chem. Lett.

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“…Although time‐dependent density functional theory (TDDFT) has become the most wide‐spread ab initio model to explore the electronically excited state properties of medium and large molecules due to its balance between computational efficiency and accuracy of results, using this model to deal with biradicals and conical intersections where double excitations play significant roles is difficult . TDDFT with certain conventional approximate functional typically underestimates the excitation energies of charge transfer (CT) states, and range‐separated (RS) functionals can be used as alternatives .…”

Section: Introductionmentioning

confidence: 99%

Why the lowest electronic excitations of rhodamines are overestimated by time‐dependent density functional theory

Zhou

2018

Int J of Quantum Chemistry

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Rhodamines are widely used as laser dyes and fluorescent probes due to their excellent photophysical and photochemical properties. Previous theoretical studies have shown that the lowest excitation energies of rhodamines are overestimated systematically by time‐dependent density functional theory (TDDFT). In this study, we first perform a TDDFT benchmark study with 21 exchange‐correlation functionals (XCFs) on a series of rhodamines and assess the performance of different types of functional in predicting the lowest excitation energies of rhodamines. Statistical results reveal that the fraction of Hartree–Fock exchange (HFX) included in the XCF is a key parameter. Pure functionals without HFX offer the best performance, with the mean absolute error (MAE) of approximately 0.1 eV. However, they provide a wrong order of the lowest nπ* and ππ* states and suffer from charge‐transfer contamination problem for rhodamine dyes (RDs) in zwitterionic form. Among the other tested functionals, popular global hybrid functional B3LYP delivers the smallest MAE of 0.36 eV. We then perform calculations with second‐order algebraic diagrammatic construction and extended multiconfiguration quasi‐degenerate perturbation theory at second‐order of PT expansion methods. Remarkably accurate results are obtained. We confirm that the reason for the overestimation of the lowest excitation energies of RDs by TDDFT method should be similar to that of cyanine dyes, and that double excitations contribute to this systematic deviation.

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“…Using spectroscopic approaches, such as the electron absorption spectroscopic technique, fluorescence methods combined with the RLS technique, and mainly measurements of fluorescence lifetimes, we have shown the complexity of physical processes that exert an impact on the observed effects. The dual fluorescence effects can be induced in different molecules by changes in medium polarity, pH of the solution, temperature, or the concentration of the sample [29–33]. According to theories attempting at elucidation of the observed fluorescence effects, they can be related to appearance of intramolecular CT states [34] and the so-called TICT states (Twisted Intramolecular Charge Transfer) [35, 36].…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Studies of Fluorescence Effects in Bioactive 4-(5-Heptyl-1,3,4-Thiadiazol-2-yl)Benzene-1,3-Diol and 4-(5-Methyl-1,3,4-Thiadiazol-2-yl)Benzene-1,3-Diol Molecules Induced by pH Changes in Aqueous Solutions

et al. 2017

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This paper presents the results of stationary fluorescence spectroscopy and time-resolved spectroscopy analyses of two 1,3,4-thiadiazole analogues, i.e. 4-(5-methyl-1,3,4-thiadiazol-2-yl)benzene-1,3-diol (C1) and 4-(5-heptyl-1,3,4-thiadiazol-2-yl)benzene-1,3-diol (C7) in an aqueous medium containing different concentrations of hydrogen ions. An interesting dual florescence effect was observed when both compounds were dissolved in aqueous solutions at pH below 7 for C1 and 7.5 for C7. In turn, for C1 and C7 dissolved in water at pH higher than the physiological value (mentioned above), single fluorescence was only noted. Based on previous results of investigations of the selected 1,3,4-thiadiazole compounds, it was noted that the presented effects were associated with both conformational changes in the analysed molecules and charge transfer (CT) effects, which were influenced by the aggregation factor. However, in the case of C1 and C7, the dual fluorescence effects were visible in a higher energetic region (different than that observed in the 1,3,4-thiadiazoles studied previously). Measurements of the fluorescence lifetimes in a medium characterised by different concentrations of hydrogen ions revealed clear lengthening of the excited-state lifetime in a pH range at which dual fluorescence effects can be observed. An important finding of the investigations presented in this article is the fact that the spectroscopic effects observed not only are interesting from the cognitive point of view but also can help in development of an appropriate theoretical model of molecular interactions responsible for the dual fluorescence effects in the analysed 1,3,4-thiadiazoles. Furthermore, the study will clarify a broad range of biological and pharmaceutical applications of these compounds, which are more frequently used in clinical therapies. Graphical AbstractUpper left corner – C7 molecule at high pH, right upper corner - fluorescence emission spectrum for C7 dissolved in H2O at high pH (7–12) - single fluorescence. Bottom left corner – C7 molecule at low pH (1–7), lower right corner - fluorescence emission spectrum for C7 dissolved in water at low pH – two fluorescence emissions. The circles indicate the group related to dissociation of molecules at low and high pH and the additional long circles indicate C1 or a molecule with a shorter acyl chain. Electronic supplementary materialThe online version of this article (doi:10.1007/s10895-017-2053-y) contains supplementary material, which is available to authorized users.

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New Insights into the Dual Fluorescence of Methyl Salicylate: Effects of Intermolecular Hydrogen Bonding and Solvation

Cited by 172 publications

References 43 publications

Rotational Spectra of Two Hydrogen-Bonded Methyl Salicylate Monohydrates: Relative Stability and Tunneling Motions

Rotational Spectra of Two Hydrogen-Bonded Methyl Salicylate Monohydrates: Relative Stability and Tunneling Motions

Why the lowest electronic excitations of rhodamines are overestimated by time‐dependent density functional theory

Spectroscopic Studies of Fluorescence Effects in Bioactive 4-(5-Heptyl-1,3,4-Thiadiazol-2-yl)Benzene-1,3-Diol and 4-(5-Methyl-1,3,4-Thiadiazol-2-yl)Benzene-1,3-Diol Molecules Induced by pH Changes in Aqueous Solutions

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