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A DFT study of pyrrole-isoxazole derivatives as chemosensors for fluoride anion.

Jin R, Sun W, Tang S - Int J Mol Sci (2012)

Bottom Line: It turned out that the unique selectivity of AIC derivatives for F(-) is ascribed to their ability of deprotonating the host sensors.Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT).The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.

View Article: PubMed Central - PubMed

Affiliation: College of Chemistry and Chemical Engineering, Chifeng University, Chifeng 024000, China; E-Mail: Cfxyhxx@163.com.

ABSTRACT
The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F(-) Cl(-), Br(-), AcO(-), and H(2)PO(4) (-)) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F(-) is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.

No MeSH data available.


Related in: MedlinePlus

Frontier molecular orbital (FMOs) of AIC and AIC− in S0 at the B3LYP/6- 31+G(d,p) level.
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f1-ijms-13-10986: Frontier molecular orbital (FMOs) of AIC and AIC− in S0 at the B3LYP/6- 31+G(d,p) level.

Mentions: It is useful to examine the frontier molecular orbitals (FMOs) of the compounds under investigation. The origin of the geometric difference introduced by excitation can be explained, at least in qualitative terms, by analyzing the change in the bonding character of the orbitals involved in the electronic transition for each pair of bonded atoms. An electronic excitation results in some electron density redistribution that affects the molecular geometry [49,50]. The qualitative molecular orbital representations of FMOs for AIC and AIC− in S0 are shown in Figure 1. The corresponding qualitative molecular orbital representations of FMOs for AIC and AIC− in S1 are shown in Figure SI, Supporting Information. The major assignments of the lowest electronic transitions for AIC and AIC− are mainly as HOMO→LUMO, which corresponds to a π–π* excited singlet state. From Figure 1, one can see that both the HOMO and LUMO of AIC and AIC− are spread over the whole conjugated molecule. A careful inspection of the results displayed in Figure 1 reveals that the vertical S0→S1 transition of AIC and AIC− shows the intramolecular charge transfer (ICT) in nature. Analysis of the FMOs for AIC and AIC− indicates that the excitation of the electron from the HOMO to LUMO makes the electronic density flow mainly from the 4,5,6,7-tetrahydro-1H-indole moiety (part A) to 3-aminoisoxazole-4-carboxamide moiety (part B). The HOMO of AIC has contributions of 69.2% and 30.8% on parts A and B, while the corresponding values of LUMO are 35.5% and 64.5%, respectively. The HOMO of AIC− has contributions of 68.9% and 31.1% on parts A and B, while the corresponding values of LUMO are 29.0% and 71.0%, respectively. Hence, the percentage of charge transfer from Parts A to B is 38.9% in AIC−, which is greater than that of 5.2% in AIC. It is obvious that deprotonation strengthens the electron-donating ability of part A, suggesting a stronger coupling between parts A and B. The molecular p-conjugation in AIC− becomes higher than that of AIC. As a consequence, the electron can move more fluently from parts A to B. This suggests that the charge-transfer character of AIC− is stronger than that of AIC. The ICT transition in the chemosensor system becomes much easier after deprotonation, resulting in a red shift between their UV-vis spectra. Similar phenomena are also found for S1 (see Figure SI). However, the intensity of fluorescence may be weak because the AIC− has a worse conjugation due to large twist angles between Parts A and B. The dihedral values of between Parts A and B for AIC and AIC− are 179.0 and 78.7° respectively, suggesting that the molecular p-conjugation in AIC− becomes lower than that of AIC. These results reveal that the deprotonation by F− has obvious effects on the distribution of FMOs, resulting in a red shift between their fluorescence spectra and decreasing the intensity of fluorescence.


A DFT study of pyrrole-isoxazole derivatives as chemosensors for fluoride anion.

Jin R, Sun W, Tang S - Int J Mol Sci (2012)

Frontier molecular orbital (FMOs) of AIC and AIC− in S0 at the B3LYP/6- 31+G(d,p) level.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3472725&req=5

f1-ijms-13-10986: Frontier molecular orbital (FMOs) of AIC and AIC− in S0 at the B3LYP/6- 31+G(d,p) level.
Mentions: It is useful to examine the frontier molecular orbitals (FMOs) of the compounds under investigation. The origin of the geometric difference introduced by excitation can be explained, at least in qualitative terms, by analyzing the change in the bonding character of the orbitals involved in the electronic transition for each pair of bonded atoms. An electronic excitation results in some electron density redistribution that affects the molecular geometry [49,50]. The qualitative molecular orbital representations of FMOs for AIC and AIC− in S0 are shown in Figure 1. The corresponding qualitative molecular orbital representations of FMOs for AIC and AIC− in S1 are shown in Figure SI, Supporting Information. The major assignments of the lowest electronic transitions for AIC and AIC− are mainly as HOMO→LUMO, which corresponds to a π–π* excited singlet state. From Figure 1, one can see that both the HOMO and LUMO of AIC and AIC− are spread over the whole conjugated molecule. A careful inspection of the results displayed in Figure 1 reveals that the vertical S0→S1 transition of AIC and AIC− shows the intramolecular charge transfer (ICT) in nature. Analysis of the FMOs for AIC and AIC− indicates that the excitation of the electron from the HOMO to LUMO makes the electronic density flow mainly from the 4,5,6,7-tetrahydro-1H-indole moiety (part A) to 3-aminoisoxazole-4-carboxamide moiety (part B). The HOMO of AIC has contributions of 69.2% and 30.8% on parts A and B, while the corresponding values of LUMO are 35.5% and 64.5%, respectively. The HOMO of AIC− has contributions of 68.9% and 31.1% on parts A and B, while the corresponding values of LUMO are 29.0% and 71.0%, respectively. Hence, the percentage of charge transfer from Parts A to B is 38.9% in AIC−, which is greater than that of 5.2% in AIC. It is obvious that deprotonation strengthens the electron-donating ability of part A, suggesting a stronger coupling between parts A and B. The molecular p-conjugation in AIC− becomes higher than that of AIC. As a consequence, the electron can move more fluently from parts A to B. This suggests that the charge-transfer character of AIC− is stronger than that of AIC. The ICT transition in the chemosensor system becomes much easier after deprotonation, resulting in a red shift between their UV-vis spectra. Similar phenomena are also found for S1 (see Figure SI). However, the intensity of fluorescence may be weak because the AIC− has a worse conjugation due to large twist angles between Parts A and B. The dihedral values of between Parts A and B for AIC and AIC− are 179.0 and 78.7° respectively, suggesting that the molecular p-conjugation in AIC− becomes lower than that of AIC. These results reveal that the deprotonation by F− has obvious effects on the distribution of FMOs, resulting in a red shift between their fluorescence spectra and decreasing the intensity of fluorescence.

Bottom Line: It turned out that the unique selectivity of AIC derivatives for F(-) is ascribed to their ability of deprotonating the host sensors.Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT).The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.

View Article: PubMed Central - PubMed

Affiliation: College of Chemistry and Chemical Engineering, Chifeng University, Chifeng 024000, China; E-Mail: Cfxyhxx@163.com.

ABSTRACT
The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F(-) Cl(-), Br(-), AcO(-), and H(2)PO(4) (-)) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F(-) is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.

No MeSH data available.


Related in: MedlinePlus