Photoenhancement of the C≡N Stretching Vibration Intensity of Aromatic Nitriles

Liu, Jingsong; Feng, Renwei; Zhou, Liang; Gai, Feng; Zhang, Wenkai

doi:10.1021/acs.jpclett.2c02418

Cited by 10 publications

(25 citation statements)

References 51 publications

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“…This large frequency shift (Δν CN ≈ 123–130 cm –1 ) clearly indicates that in both cases, the electronic excited single state(s) accessed via UV excitation has a strong CT character, resulting in an increase in the local charge density on the nitrile group. As observed in a previous study, this charge increase on the nitrile group leads to a significant enhancement in its oscillator strength. Moreover, as shown (Figures S5 and S6), the decay kinetics of the nitrile stretching bands of these two indole derivatives match their respective fluorescence decay kinetics, hence indicating that in both cases, the fluorescence state is L a in DMSO.…”

Section: Resultssupporting

confidence: 83%

C≡N Stretching Frequency as a Convenient Reporter of Charge Separation in Molecular Systems

et al. 2023

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Previously, several studies have shown that, for a set of structurally related nitrile compounds, there could be a linear relationship between the total charge on the nitrile group (q CN) and its stretching frequency (νCN). However, it is unclear whether the corresponding frequency and charge properties of structurally different nitrile compounds can be described by a single linear νCN–q CN relationship. Herein, we compute the q CN magnitudes of a large number of nitrile-containing molecules whose νCN values cover a spectral range of ca. 200 cm–1 and are measured under different experimental conditions. Our results reveal that νCN indeed exhibits a linear dependence on q CN, with a slope of 637 ± 30 cm–1/charge. Because the nitrile moiety is a commonly used building block in electronic donor–acceptor (D–A) molecular systems, we believe that this linear relationship will find utility in a wide range of applications where such D–A constructs are used, such as in organic photovoltaic assemblies. In addition, we apply this linear relationship to characterize the degree of charge transfer upon photoexcitation of two indole derivatives, 5-cyanoindole and 6-cyanoindole, and are able to show that in both cases, the fluorescence emission arises from a charge-transfer or La state.

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Section: Resultssupporting

confidence: 83%

C≡N Stretching Frequency as a Convenient Reporter of Charge Separation in Molecular Systems

et al. 2023

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“…In our study, a significant photoenhancement of the nitrile stretching vibration is observed for the MCLT excited state of 1 formed upon 400 nm excitation (Figure 3). A similar enhancement has been observed for aromatic nitriles 80 and CN substituted bipyridyl complexes of ruthenium(II). 81,82 However, this is the first time that such an effect is reported for an intercalating probe.…”

Section: ■ Discussionsupporting

confidence: 80%

“…The notable enhancement of the molar absorptivity of the ν(C�N) vibration in the excited state is in agreement with recent observations for indole substituted nitriles and linked to the electron density in the aromatic system. 80 The transient band is shifted to a lower wavenumber by ca. 18 cm −1 from the position of the bleach ground state absorption, indicating the presence of a weaker CN bond in the 3 MLCT* excited state relative to the ground state.…”

Section: ■ Resultsmentioning

confidence: 98%

Good Vibrations Report on the DNA Quadruplex Binding of an Excited State Amplified Ruthenium Polypyridyl IR Probe

Stitch,

Avagliano,

Graczyk

et al. 2023

J. Am. Chem. Soc.

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The nitrile containing Ru(II)polypyridyl complex [Ru(phen) 2 (11,] 2+ (1) is shown to act as a sensitive infrared probe of G-quadruplex (G4) structures. UV−visible absorption spectroscopy reveals enantiomer sensitive binding for the hybrid htel(K) and antiparallel htel(Na) G4s formed by the human telomer sequence d[AG 3 (TTAG 3 ) 3 ]. Time-resolved infrared (TRIR) of 1 upon 400 nm excitation indicates dominant interactions with the guanine bases in the case of Λ-1/htel(K), Δ-1/htel(K), and Λ-1/htel(Na) binding, whereas Δ-1/htel(Na) binding is associated with interactions with thymine and adenine bases in the loop. The intense nitrile transient at 2232 cm −1 undergoes a linear shift to lower frequency as the solution hydrogen bonding environment decreases in DMSO/water mixtures. This shift is used as a sensitive reporter of the nitrile environment within the binding pocket. The lifetime of 1 in D 2 O (ca. 100 ps) is found to increase upon DNA binding, and monitoring of the nitrile and ligand transients as well as the diagnostic DNA bleach bands shows that this increase is related to greater protection from the solvent environment. Molecular dynamics simulations together with binding energy calculations identify the most favorable binding site for each system, which are in excellent agreement with the observed TRIR solution study. This study shows the power of combining the environmental sensitivity of an infrared (IR) probe in its excited state with the TRIR DNA "site effect" to gain important information about the binding site of photoactive agents and points to the potential of such amplified IR probes as sensitive reporters of biological environments.

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“…However, unlike in the case of 7AI, we did not observe a detectable “tautomer” emission band for 4CN7AI in alcohols (Figure S5). In addition, a recent time-resolved infrared (IR) study by Liu et al . also indicated that there is no detectable “tautomer” population at the electronically excited state(s) of 4CN7AI.…”

Section: Resultsmentioning

confidence: 99%

“…However, unlike in the case of 7AI, we did not observe a detectable "tautomer" emission band for 4CN7AI in alcohols (Figure S5). In addition, a recent timeresolved infrared (IR) study by Liu et al 39 there is no detectable "tautomer" population at the electronically excited state(s) of 4CN7AI. Taken together, these findings suggest that if a "tautomer" of 4CN7AI is formed via a double proton transfer process in protic solvents at its electronically excited state(s), this "tautomer" species must decay to the ground electronic state on an ultrafast timescale.…”

Section: Methodsmentioning

confidence: 99%

Photophysics of Two Indole-Based Cyan Fluorophores

et al. 2023

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For the purpose of searching for new biological fluorophore, we assess the photophysical properties of two indole derivatives, 4-cyano-7-azaindole (4CN7AI) and 1-methyl-4-cyano-7-azaindole (1M4CN7AI), in a series of solvents. We find that (1) the absorption spectra of both derivatives are insensitive to solvents and are red-shifted from that of indole, having a maximum absorption wavelength of ca. 318 nm and a broad profile that extends beyond 370 nm; (2) both derivatives emit in the blue to green spectral range with a large Stokes shift, for example, in H2O, the maximum emission wavelength of 4CN7AI (1M4CN7AI) is at ca. 455 nm (470 nm); (3) 4CN7AI has a higher fluorescence quantum yield (QY) and a longer fluorescence lifetime (τF) in aprotic solvents than in protic solvents, for example, QY (τF) = 0.72 ± 0.04 (7.6 ± 0.8 ns) in tetrahydrofuran and QY (τF) = 0.29 ± 0.03 (6.2 ± 0.6 ns) in H2O; (4) in all of the solvents used except H2O, the fluorescence QY (τF) of 1M4CN7AI is equal to or higher (longer) than 0.69 ± 0.03 (11.2 ± 0.7 ns). Taken together, these results suggest that the corresponding non-natural amino acids, 4-cyano-7-azatryptophan and 1-methyl-4-cyano-7-azatryptophan, could be useful as biological fluorophores.

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Photoenhancement of the C≡N Stretching Vibration Intensity of Aromatic Nitriles

Cited by 10 publications

References 51 publications

C≡N Stretching Frequency as a Convenient Reporter of Charge Separation in Molecular Systems

C≡N Stretching Frequency as a Convenient Reporter of Charge Separation in Molecular Systems

Good Vibrations Report on the DNA Quadruplex Binding of an Excited State Amplified Ruthenium Polypyridyl IR Probe

Photophysics of Two Indole-Based Cyan Fluorophores

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