As reversible fluorescent probes, HTP-1 and HTP-2 have favourable applications for the detection of Zn
and H
S. Herein, the impact of solvent on the excited-state intramolecular proton transfer ...(ESIPT) of HTP-1 and HTP-2 was comprehensively investigated. The obtained geometric parameters and infrared (IR) vibrational analysis associated with the intramolecular hydrogen bond (IHB) indicated that the strength of IHB for HTP-1 was weakened in the excited state. Moreover, structural torsion and almost no ICT behaviour indicated that the ESIPT process did not occur in HTP-1. Nevertheless, when the 7-nitro-1,2,3-benzoxadiazole (NBD) group replaced the H atom, the IHB strength of HTP-2 was enhanced after photoexcitation, which inhibited the twisting of tetraphenylethylene, thereby opening the ESIPT channel. Notably, hole-electron analysis and frontier molecular orbitals revealed that the charge decoupling effect was the reason for the fluorescence quenching of HTP-2. Furthermore, the potential energy curves (PECs) revealed that HTP-2 was more inclined to the ESIPT process in polar solvents than in nonpolar solvents. With a decrease in solvent polarity, it was more conducive to the ESIPT process. Our study systematically presents the ESIPT process and different detection mechanisms of the two reversible probe molecules regulated by solvent polarity, providing new insights into the design and development of novel fluorescent probes.
The mechanism of fluorescence detection of diethyl chlorophosphate (DCP) based on 2-substituted benzothiazole (BZ-DAM) was studied by a theoretical calculation method. It should not be ignored that ...both the BZ-DAM and the detection product BZ-CHO have two excited-state intramolecular proton transfer (ESIPT) channels. Density functional theory (DFT) and time-dependent DFT (TDDFT) theory were used to study the photophysical mechanism of two compounds in two channels in (acetonitrile) ACN solvent, and the temperature dependence of the two channels was given. Channel 1 is more likely to exist at low temperatures and channel 2 is more likely to exist at high temperatures. By theoretical analysis of the constructed potential energy curve, the hydrogen bond energy and electron-hole analysis, we confirmed that both molecules undergo ESIPT and intramolecular charge transfer (ICT) processes in channel 1 and ESIPT and twisted intramolecular charge transfer (TICT) coupling processes in channel 2. The formation of product BZ-CHO molecules led to a significant fluorescence blue-shift phenomenon and inhibited the ICT process, which confirmed that BZ-DAM could be used as a fluorescence probe for fluorescence detection. We sincerely hope that this work will not only help to clarify the excited-state dynamics behavior of the BZ-DAM probe but also provide a new idea for designing and optimizing a new chemical dosimeter.
DFT and TD-DFT were used in this article to investigate the effects of different substitutions at multiple sites on the photophysical mechanism of bis-HBX in the gas phase. Four different ...substitution modes were selected, denoted as A1 (X=Me, Y=S), A2 (X=OMe, Y=S), B1 (X=Me, Y=NH), and C1 (X=Me, Y=O). The geometric parameters proved that the IHBs enhanced after photoexcitation, which was conducive to promote the ESIPT process. Combining the analysis of the PECs, it was revealed that the bis-HBX molecule underwent the ESIPT process, and the ease of the ESIPT process was in the order of A1 > A2> B1 > C1. In particular, the TICT process in A1 and B1 promoted the occurrence of the ESIPT process. In addition, the IC process was identified, particularly in C1. Meanwhile, the calculation of fluorescence lifetime and fluorescence rate further confirmed that A1 was the most effective fluorescent probe molecule. This theoretical research provides an innovative theoretical reference for regulating ESIPT reactions and optimizing fluorescent probe molecules.
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•The probe DPA-CI showed significant TICT, leading to the fluorescence quenching.•The fixed benzimidazole moiety weakens the TICT in the product DPA-CI-PS.•AIE properties are ...confirmed in DPA-CI-PS, resulting in fluorescence enhancement.•The detection mechanism based on TICT and AIE properties was clearly elucidated.
The DPA-CI molecule is a novel fluorescent sensing probe synthesized with TICT and AIE properties. It can detect phosgene, generating DPA-CI-PS. We investigated their photophysical mechanisms in THF solvent using DFT and TD-DFT methods. Large torsion angles and noticeable charge separation confirmed that the TICT occurs in DPA-CI. Due to the formation of a robust cyclic structure, the TICT is inhibited in DPA-CI-PS. Besides, based on NBO analysis, we demonstrated that DPA-CI-PS exhibits significant AIE characters. This work clearly illuminates the detection mechanism, which offers theoretical insights valuable for developing efficient fluorescent sensing probes.
•BPDC undergoes the concerted ESDPT process in CHY and H2O solvents.•The concerted ESDPT process of BPDC is induced at 62 fs (CHY) and 19 fs (H2O).•The IEHBs formed by BPDC and H2O accelerates the ...ESDPT process.
This study has conducted a systematic investigation into the excited state double proton transfer (ESDPT) process of 2,2′-bipyridine-3,3′-diol-5,5′-dicarboxylate acid ethyl ester (BPDC) in cyclohexane (CYH) and water (H2O) by density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The calculated geometrical parameters, reduced density gradient and infrared vibration spectra confirm that BPDC undergoes the ESDPT process in both CYH and H2O. In comparison to the CYH solvent, the intramolecular hydrogen bonds (IAHBs) are strengthened in the S0 state by the formation of centrosymmetric intermolecular hydrogen bonds (IEHBs) between H2O and the OH group of BPDC molecules. Furthermore, the constructed potential energy surfaces show that BPDC molecules undergo a concerted ESDPT process without potential barriers in both solvents. Time evolution analysis confirms that the ESDPT process of BPDC molecules in H2O solvent (19 fs) is faster than that in CYH solvent (62 fs). The results indicate that the formation of IEHBs causes zero disruption to the original I AHBs, but it can effectively promote the ESDPT process of BPDC molecules. Overall, this work serves as important theoretical guidance for the development of high-performance fluorescence materials.
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In view of the application prospects in biomedicine of (E)-1-(4-(diethyla-mino)-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide (DAHTS), the behavior of excited-state dynamics and photophysical ...properties were studied using the density functional theory/time-dependent density functional theory method. A series of studies indicated that the intramolecular hydrogen-bond (IHB) intensity of DAHTS was enhanced after photoexcitation. This was conducive to promoting the excited-state intramolecular proton-transfer (ESIPT) process. Combining the analysis of the IHB and hole–electron, it revealed that the molecule underwent both the ESIPT process and the twisted charge-transfer (TICT) process. Relying on exploration of the potential energy surface, it was proposed that the different competitive mechanisms between the ESIPT and TICT processes were regulated by solvent polarity. In acetonitrile (ACN) solvent, the ESIPT process occurred first, and the TICT process occurred later. In contrast, in the CYH solvent, the molecule first underwent the TICT process and then the ESIPT process. Furthermore, we raised the possibility that the TICT behavior was the cause of weak fluorescence emission for the DAHTS in CYH and ACN solvents. By the dimer correlation analysis, the corresponding components of triple fluorescence emission were clearly assigned, corresponding to the monomer, dimer, and ESIPT isomer in turn. Our work precisely elucidated the photophysical mechanism of DAHTS and the attribution of the triple fluorescence emission components, which provided valuable guidance for the development and regulation of bioactive fluorescence probes with multiband and multicolor emission characteristics.
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•TPASB-1 triggers the TICT process due to the substitution at R1.•The substitution at R1 successfully turn on the ESIPT process at R2 for TPASB-2.•The ESIPT process in TPASB-2 has the ...lowest barrier due to the substitution at R1.
The triphenylamine Schiff-base (TPASB) with dual proton transfer sites (N1…H1–O1 R1 and N2…H2–O2 R2), which is crucial in the field of optoelectronic materials. Herein, a novel molecular design strategy for preparing of TPASB-1 and TPASB-2 via the selective methylation of the hydroxyl group at the R2 or R1 position was proposed. The analysis of electronic structures and potential energy surfaces revealed that a single excited state intramolecular proton transfer (ESIPT) process of TPASB occurs only at R1. Nevertheless, the ESIPT process of TPASB-2 was successfully turned on at R2. More noteworthy is that compared to TPASB, the methylation of hydroxyl group at the R2 position triggers the TICT process of TPASB-1, effectively reducing the potential barrier of ESIPT at the R1 position. This theoretical study explains the role of the substituent effect in regulating ESIPT behaviour, and provides valuable guidance for synthesising efficacious ESIPT-active compounds.
•DP-HPPI undergoes reversible ESIPT process in DCM.•ESIPT is prohibited due to the involvement of intermolecular hydrogen bonding in ACN.•Intermolecular hydrogen bonding initiates the TICT process of ...DP-HPPI in ACN.
Intermolecular hydrogen bonding prominently figures in numerous photophysical and photochemical processes. It is worth discussing whether it can act as a switch to effectively convert excited-state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) process. In this paper, the effect of intermolecular hydrogen bonding on the ESIPT and TICT process of DP-HPPI in DCM and ACN solvent has been explored by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The analytical results show that DP-HPPI experiences the ESIPT process via intramolecular hydrogen bonding in DCM. However, the ESIPT process is prohibited due to the involvement of intermolecular hydrogen bonding in ACN, triggering the TICT process. From the study results of photophysical properties in DP-HPPI, we reveal that DP-HPPI undergoes reversible ESIPT in DCM. Moreover, we elucidate the detailed proton transfer pathway and the advantage of reverse proton transfer over forward proton transfer. Notably, an unobstructed TICT process occurs in the S1 state after light irradiation of DP-HPPI in ACN. Our work successfully closes the ESIPT process and initiates the TICT process via intermolecular hydrogen bonding, and provides new insights into the design and synthesis of efficient optical devices.
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•AFBD experiences a cooperative ESIDPT process in acetonitrile solvent.•The cooperative ESIDPT is converted into stepwise ESIDPT by introducing –Br or –OCH3.•The substitution of electronic groups ...OCH3→H→Br can accelerate the ESIDPT process.
In this paper, the effect of different electronic group substituents on the excited state intramolecular double proton transfer (ESIDPT) in AFBD is comprehensively researched by using quantum chemistry methods. Two electronic groups with comparable capabilities, including the electron-withdrawing group (-Br) and the electron-donating group (–OCH3), are chose to accomplish this study. The obtained geometric parameters, reduced density gradient and infrared spectra calculations have demonstrated that AFBD and its two derivatives experience the ESIDPT process. Subsequently, the conclusion of the potential energy surface and Bonn-Oppenheimer molecular dynamics further unveil that AFBD undergoes a cooperative ESIDPT process at ∼15 fs. Nevertheless, it should be noted that the introduction of -Br and –OCH3 transforms the proton transfer path. That is: "the cooperative ESIDPT is converted into the stepwise ESIDPT". Besides, we also confirm that the substitution of the electronic groups OCH3→H→Br can accelerate the ESIDPT process. Our work not only regulates the path of ESIDPT process, but also provides a time scale for this process, which is conducive to developing new intelligent fluorophores based on ESIDPT behavior.
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•The TICT process is responsible for the fluorescence quenching of the TB-N2H4.•The product TB-OH undergoes the stepwise ESDPT process in EtOH solvent.•The ESDPT induces fluorescence ...activation of TB-OH by disrupting the TICT process.•The fluorescence “turn-on” mechanism for probe TB-N2H4 was successfully clarified.
The Density functional theory (DFT) and time-dependent DFT methods are used to study the detection mechanism of the fluorescent probe TB-N2H4 and its product TB-OH in ethanol (EtOH) solvent. For the TB-N2H4, EtOH can form dual intermolecular hydrogen bonds (IHBs) with TB-N2H4 at two locations (X and Y). The geometric structure and charge distribution show that the TB-N2H4 undergoes a twisted intramolecular charge transfer (TICT) process, resulting in the fluorescence quenching of TB-N2H4. In contrast, for the TB-OH, EtOH can only form IHBs with TB-OH at one site (X). The charge distribution show that intramolecular charges redistributed between the proton donor and proton acceptor groups, providing the driving force for the proton transfer process. The TICT is inhibited by excited-state dual proton transfer (ESDPT) process of TB-OH, resulting in the appearance of new fluorescence. Moreover, the results obtained from the potential energy curves manifest that the stepwise ESDPT process.
