Reduced fluorescence quenching of coumarin 102 at higher phenol mole fractions in cyclohexane–phenol and anisole–phenol solvent mixtures: role of competitive hydrogen bonding

Barman, Nabajeet; Sahu, Kalyanasis

doi:10.1039/c4ra11251b

Cited by 16 publications

(17 citation statements)

References 37 publications

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“…25 Recently, we have also observed similar anomalous fluorescence quenching Paper PCCP of C102 in a cyclohexane-phenol mixture. 30 Like AN, phenol can also drive H-assisted PET to C102 and may also form higher order complexes at high mole fractions. Similarity of the trend of fluorescence quenching of the C102-AN and C102-phenol pairs reinforces our claim of the H-bond guided modulation of PET.…”

Section: Introductionmentioning

confidence: 99%

Anomalous modulation of photoinduced electron transfer of coumarin 102 in aniline–dimethylaniline mixture: dominant role of hydrogen bonding

Barman

Sahu

2014

Phys. Chem. Chem. Phys.

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In a previous study, we reported a striking observation that photoinduced electron transfer (PET) from aniline (AN) to photoexcited coumarin 102 (C102) can be accelerated by adding an inert component (cyclohexane or toluene) to the neat electron donor solvent AN (Phys. Chem. Chem. Phys., 2014, 16, 6159-6166). The H-bond linking the electron donor (D, AN) and the acceptor (A, C102) was proposed to dictate the PET process. To account for the unusual variation of quenching pattern with AN mole fraction, two possible reasons were cited - (1) the D-A (AN-C102) H-bonding may be modulated due to change in polarity of the medium or (2) the additional D-D (AN-AN) H-bonding may restrain the D-A H-bonding to adjust optimally for the PET. Here, we investigate the PET of C102 in an AN-dimethylaniline (DMA) mixture to negate the polarity variation. Since, both AN and DMA have similar polarities, the polarity of the mixture should remain invariant at all compositions. Nevertheless, we found that the fluorescence quantum yield and lifetime of C102 in the mixtures follows a similar unusual trend as observed earlier in the AN-toluene or AN-cyclohexane mixtures; it first decreases up to a particular mole fraction (XD) of the H-bond donor AN and, thereafter, increases on further enrichment of the donor. The observed PET modulation may be rationalized by considering efficient PET in the 1 : 1 H-bonded C102-AN complex but less efficient PET in higher order C102-(AN)n≥2 complexes, where additional D-D (AN-AN) H-bonding may influence the key C102-AN H-bonding and thus inhibit the PET process.

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Section: Introductionmentioning

confidence: 99%

Anomalous modulation of photoinduced electron transfer of coumarin 102 in aniline–dimethylaniline mixture: dominant role of hydrogen bonding

Barman

Sahu

2014

Phys. Chem. Chem. Phys.

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“…6 and Table 2). Although we have speculated that D-A H-bonding becomes favourable at some intermediate mole fraction in the presence of a non-interacting co-solvent in our previous studies 5,18 but it is for the first time, we explicitly show this here by MD simulation. The simulation indicates that cyclohexane reduces D-D H-bonding and enhances D-A H-bonding at an intermediate mole fraction compared to neat aniline.…”

Section: Molecular Dynamics (Md) Simulationmentioning

confidence: 63%

“…Thus, the closest donor-acceptor approach may be similar in both cases (AN and DMA) and, hence, PET rate variation in the two systems may possibly hint at any other effect of H-bonding on PET rather than just controlling the donor-acceptor proximity. 5,6 Yoshihara and co-workers studied PET of a series of coumarin fluorophores in neat AN and DMA solvents. 7 They found faster PET in DMA than in AN for all coumarins, which they attributed to the better electron donating ability of DMA compared to AN (oxidation potentials of AN and DMA in acetonitrile are 0.93 V and 0.76 V vs. SCE, respectively 7 ).…”

Section: Introductionmentioning

confidence: 99%

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Modulation of ultrafast photoinduced electron transfer in H-bonding environment: PET from aniline to coumarin 153 in the presence of an inert co-solvent cyclohexane

Barman

Hossen

Mondal

et al. 2015

Phys. Chem. Chem. Phys.

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Despite intensive research, the role of the H-bonding environment on ultrafast PET remains illusive. For example, coumarin 153 (C153) undergoes ultrafast photoinduced electron transfer (PET) in electron-donating solvents, in both aniline (AN) and N,N-dimethylaniline (DMA), despite their very different H-bonding abilities. Thus, donor-acceptor (AN-C153) H-bonding may have only a minor role in PET (Yoshihara and co-workers, J. Phys. Chem. A, 1998, 102, 3089). However, donor-acceptor H-bonding may be somehow less effective in the neat H-bonding environment but could become dominant in the presence of an inert solvent (Phys. Chem. Chem. Phys., 2014, 16, 6159). We successfully applied and tested the proposal here. The nature of PET modulation of C153 in the presence of a passive component cyclohexane is found to be very different for aniline and DMA. Upon addition of cyclohexane to DMA, the PET process gradually becomes retarded but in the case of AN, the PET rate was indeed found to be accelerated at some intermediate composition (mole fraction of aniline, XAN∼ 0.74) compared to that of neat aniline. It is intuitive that cyclohexane may replace some of the donors (AN or DMA) from the vicinity of the acceptor and, thus, should disfavour PET. However, in the hydrogen bonding environment using molecular dynamics simulation, for the first time, we show that the average number of aniline molecules orienting their N-H group in the proximity of the C=O group of C153 is actually higher at the intermediate mole fraction (0.74) of aniline in a mixture rather than in neat aniline. This small but finite excess of C153-AN H-bonding already present in the ground state may possibly account for the anomalous effect. The TD-DFT calculations presented here showed that the intermolecular H-bonding between C153 and AN strengthens from 21.1 kJ mol(-1) in the ground state to 33.0 kJ mol(-1) in the excited state and, consequently, H-bonding may assist PET according to the Zhao and Han model. Thus, we not only justified both the theoretical prediction (efficient H-bond assisted PET within the C153-AN pair) and experimental observation (minor H-bond assisted PET in neat solvent) but also established our previous hypothesis that an inert co-solvent can enhance the effect of H-bonding from molecular insights.

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“…In STED microscopy, the duration of pulses is an important factor affecting the depletion efficiency (Leutenegger et al ., ). Here, the durations of the pulses (

t_{p}

) of both excitation and depletion beams were larger than 2 ms. Because

t_{p}

was much larger than the fluorescence lifetime (∼3 ns) of Coumarin 102 dye (Barman & Sahu, ), our STED system could be considered as CW STED;

t_{p}

has insignificant influence on the depletion process of our STED system.…”

Section: Methodsmentioning

confidence: 99%

Parametric investigations on the saturation intensity of Coumarin 102 for stimulated emission depletion application

Qin

Zhao

Zhang

et al. 2018

Journal of Microscopy

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Stimulated emission depletion (STED) microscopy performed using continuous-wave (CW) lasers has been investigated and developed by Willig et al. (Nature Methods, 2007, 4(11):915) for nearly a decade. Kuang et al. (Review of Scientific Instruments, 2010, 81:053709) developed the CW STED microscopy technique with 405 nm excitation and 532 nm depletion beams. In their research, Coumarin 102 dye was adopted and was found to be depletable. In this study, a parametric investigation of the depletion of Coumarin 102 dye is carried out experimentally. The influence of the excitation and depletion beam intensities and dye concentrations on the depletion efficiency are studied in detail. The results indicate the following: (1) The highest depletion occurs for the 100 μM Coumarin 102 solution, with a 1.4 μW excitation beam and a 115.3 mW depletion beam. (2) The minimum saturation intensity (Is) of STED, that is 13 MW cm , is observed when the Coumarin 102 solution concentration is 10 μM. (3) Is values calculated directly from the depletion power derived with the cross-sectional area due to the full-width-at-half-maximum (FWHM) of the depletion beam show poor accuracy, where Is may be overestimated. Thus, a correction factor for the cross-sectional area is proposed. We also find that Is is not exactly constant for a fixed excitation beam power and dye concentration. This trend indicates that the conventional suppression function η(x)=e- ln (2)ISTED(x)/Is derived from picosecond STED may cause errors in evaluating the depletion process in CW STED microscopy.

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Reduced fluorescence quenching of coumarin 102 at higher phenol mole fractions in cyclohexane–phenol and anisole–phenol solvent mixtures: role of competitive hydrogen bonding

Cited by 16 publications

References 37 publications

Anomalous modulation of photoinduced electron transfer of coumarin 102 in aniline–dimethylaniline mixture: dominant role of hydrogen bonding

Anomalous modulation of photoinduced electron transfer of coumarin 102 in aniline–dimethylaniline mixture: dominant role of hydrogen bonding

Modulation of ultrafast photoinduced electron transfer in H-bonding environment: PET from aniline to coumarin 153 in the presence of an inert co-solvent cyclohexane

Parametric investigations on the saturation intensity of Coumarin 102 for stimulated emission depletion application

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