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Experimental absorption (l abs ) and fluorescence maxima (l fluo ), extinction coefficient 3 and fluorescence quantum yield F F for 6-H, 6-Cl and 6-Br dissolved in acetonitrile
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The photophysical properties of three 3-diethylphosphonocoumarin derivatives are studied by transient absorption spectroscopy and DFT calculations. The measured lifetime of the first excited singlet state changes upon halogen substitution at the 6-position from 40 ps for the unsubstituted compound to 100 ps for Cl and 24 ps for Br. This observation...
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... Fig . 1B shows the molar absorption coefficients, 3, and the corresponding uorescence intensities, which represent each an average over several individually prepared solutions (see also Table 1). The molar absorption coefficients are retrieved from the absorption maxima in the wavelength range above 300 nm, shown in Fig. 1C. ...Context 2
... increases the uorescence signal threefold and fourfold with respect to 6-H and 6-Br, respectively. The uorescence quantum yield F F (see Table 1) also has a larger value for 6-Cl (1.01%) than for 6-H (0.34%) and 6-Br (0. ...Context 3
... lifetime increases from 40 ps for 6-H to 100 ps for 6-Cl, and then decreases to 24 ps for 6-Br. This observation agrees with the extracted uorescence QY (see Table 1), however, seems to be in contradiction to the HAE, where a shorter singlet lifetime would be expected for molecules including heavier halogen atoms. The overall low lifetimes and uorescence QY can be related to a strong contribution of internal conversion as nonradiative relaxation process. ...Context 4
... qualitative comparison of the S 1 -lifetimes with the uo-rescence QYs (Table 1) reveals a strong correlation, i.e. clearly enhanced values for 6-Cl, and thus manifests itself in an anomaly of the HAE. In contrast, the estimated singlet-triplet QY grows according to the atomic number of the 6-substituted atom, reecting exactly the HAE. ...Context 5
... oscillator strengths are calculated according to a vertical transition (molecular structure optimized to the ground state) and shown in Table 2. We emphasize that the scaling of the calculated wavelengths leads to almost perfect matching between calculated and experimentally measured absorption wavelengths for all three compounds (cf . Tables 1 and 2), which additionally validates the DFT ...Context 6
... contrast, the LUMO does not change signicantly upon halogen substitution. The halogen substituent at 6-position reduces the oscillator strengths for excitation by almost 30% (see Table 2) in agreement with the experimentally observed change in the molar extinction coefficients (Table 1). ...Citations
Coumarin-based fluorescent agents play an important role in the manifold fundamental scientific and technological areas and need to be carefully studied. In this research, linear photophysics, photochemistry, fast vibronic relaxations, and two-photon absorption (2PA) of the coumarin derivatives, methyl 4-[2-(7-methoxy-2-oxo-chromen-3-yl)thiazol-4-yl]butanoate (1) and methyl 4-[4-[2-(7-methoxy-2-oxo-chromen-3-yl)thiazol-4-yl]phenoxy]butanoate (2), were comprehensively analyzed using stationary and time-resolved spectroscopic techniques, along with quantum-chemical calculations. The steady-state one-photon absorption, fluorescence emission, and excitation anisotropy spectra, as well as 3D fluorescence maps of 3-hetarylcoumarins 1 and 2 were obtained at room temperature in solvents of different polarities. The nature of relatively large Stokes shifts (∼4000-6000 cm-1), specific solvatochromic behavior, weak electronic π → π* transitions, and adherence to Kasha's rule were revealed. The photochemical stability of 1 and 2 was explored quantitatively, and values of photodecomposition quantum yields, on the order of ∼10-4, were determined. A femtosecond transient absorption pump-probe technique was used for the investigation of fast vibronic relaxation and excited-state absorption processes in 1 and 2, while the possibility of efficient optical gain was shown for 1 in acetonitrile. The degenerate 2PA spectra of 1 and 2 were measured by an open aperture z-scan method, and the maximum 2PA cross-sections of ∼300 GM were obtained. The electronic nature of the hetaryl coumarins was analyzed by quantum-chemical calculations using DFT/TD-DFT level of theory and was found to be in good agreement with experimental data.
Quantum-chemical calculations on the spectral properties of some aryl substituted 3-phosphonocoumarins were performed, and the effect of the substituents in the aryl moiety was evaluated. The structures possessing promising fluorescent properties were successfully synthesized via Suzuki and Sonogashira cross-coupling. The synthetic protocol was also applied for the phosphorous chemoisomer of 3-phosphonocoumarin, 1,2-benzoxaphosphorin, and their carboxylate analogues. The optical properties of the arylated and alkynylated products were experimentally determined. The obtained quantum-chemical and experimental results give the possibility for a fine tuning of the optical properties of phosphorous-containing coumarin systems by altering the substituent at its C-6 position.
The rational design of cyanine dyes for the fine-tuning of their photophysical properties undoubtedly requires theoretical considerations for understanding and predicting their absorption and fluorescence characteristics. The present study aims to assess the applicability and accuracy of several DFT functionals for calculating the absorption and fluorescence maxima of monomethine cyanine dyes. Ten DFT functionals and different basis sets were examined to select the proper theoretical model for calculating the electronic transitions of eight representative molecules from this class of compounds. The self-aggregation of the dyes was also considered. The pure exchange functionals (M06L, HFS, HFB, B97D) combined with the triple-zeta basis set 6-311+G(2d,p) showed the best performance during the theoretical estimation of the absorption and fluorescent characteristics of cyanine dyes.
Since green fluorescent protein (GFP) has revolutionized molecular and cellular biology for about three decades, there has been a keen interest in understanding, designing, and controlling the fluorescence properties of GFP chromophore (i.e., HBDI) derivatives from the protein matrix to solution. Amongst these cross-disciplinary efforts, the elucidation of excited-state dynamics of HBDI derivatives holds the key to correlating the light-induced processes and fluorescence quantum yield (FQY). Herein, we implement steady-state electronic spectroscopy, femtosecond transient absorption (fs-TA), femtosecond stimulated Raman spectroscopy (FSRS), and quantum calculations to study a series of mono- and dihalogenated HBDI derivatives (X = F, Cl, Br, 2F, 2Cl, and 2Br) in basic aqueous solution, gaining new insights into the photophysical reaction coordinates. In the excited state, the halogenated "floppy" chromophores exhibit an anti-heavy atom effect, reflected by strong correlations between FQY vs. Franck-Condon energy (EFC) or Stokes shift, and knr vs. EFC, as well as a swift bifurcation into the I-ring (major) and P-ring (minor) twisting motions. In the ground state, both ring-twisting motions become more susceptible to sterics and exhibit spectral signatures from the halogen-dependent hot ground-state absorption band decay in TA data. We envision this type of systematic analysis of the halogenated HBDI derivatives to provide guiding principles for the site-specific modification of GFP chromophores, and expand design space for brighter and potentially photoswitchable organic chemical probes in aqueous solution with discernible spectral signatures throughout the photocycle.
Owing to the growing interest in the development of novel triplet sensitizers, the introduction of arylselanyl (ArSe) groups at the 2 and 7 positions of bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene) hydrazine (BOPHY) scaffold was investigated for producing dyes1and2. Direct Se-C bond formation was effective in facilitating the intersystem crossing (ISC) channel to the corresponding triplet state, endowing them with triplet sensitization. The quantum yield (ΦΔ) of the singlet oxygen (¹O2) generation was determined using diphenylisobenzofuran (DPBF), resulting in preferableΦΔvalues of 73% and 74% for1and2, respectively, which were significantly higher than those of halogenated BOPHY. This was ascribed to the selenium-based heavy-atom effect on the photophysical properties of BOPHY dye, which was rationalized by estimating the spin-orbit coupling (SOC) values of the S1→Tntransitions. The favorable ability to generate¹O2under photoirradiation motivated us to apply the dye as a sensitizer to triplet-triplet annihilation upconversion (TTA-UC). Photoexcitation of a toluene solution of1and 9,10-diphenylanthracene (DPA) as the triplet energy acceptor with a 524 nm-wavelength laser allowed to detect upconverted emission withλemvalues of 412 nm and 430 nm, which were attributed to the DPA fluorescence. A significant anti-Stokes shift of approximately 94 nm was observed in the UC process with a of 3.9%. This study suggests that a judicious introduction of ArSe units into chromophores provides a facile but effective strategy for designing triplet sensitizers. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2021.
