Insight into the excited-state intramolecular double-proton transfer of the 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol: one-step or stepwise mechanism?

Interplay of Dual-Proton Transfer Relay to Achieve Full-Color Panel Luminescence in Excited-State Intramolecular Proton Transfer (ESIPT) Fluorophores

A new design was applied for the facile synthesis of pure organic photoluminescent molecules with dual excited-state intramolecular proton transfer (ESIPT) sites. In this novel class of emitters, full-color panel emission from blue, green, and yellow to red, including white light, can be achieved in different solvents as modulated by the enol-keto(1st)-keto(2nd) tautomer emissions. A comprehensive transient photophysical study verifies that keto(1st) and keto(2nd) have a precursor (<0.8 ps)-successor (∼20 ps)-relayed absorbance relationship, and then a fast equilibrium between the two is established, resulting in dual emissions in the nanosecond scale (∼1900 ps). Through the research on copper ions' selective PL response, the dual-ESIPT mechanism was further verified; in addition, the study of solid-state PL changes upon the stimulus of organic vapor manifests the potential application sensitivity of the molecules as dual-ESIPT sensors. Theoretical results including reaction potential energy surface analyses manifest the fact that dual-proton transfer goes along a sequential route with a smaller energy barrier, firmly supporting the experimental results. An intrinsic system that undergoes intramolecular double proton relayed transfer is thus established for the achievement of much broadened optical responses and full-color display, providing reference for the design and application of advanced dual-ESIPT optical materials.

A new interpretation of the ESIPT mechanism of 2-(benzimidazol-2-yl)-3-hydroxychromone derivatives

The present study demonstrates the excited-state intramolecular proton transfer (ESIPT) mechanism of 2-(benzimidazol-2-yl)-3-hydroxychromone (DH3B2) is based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. We find that DH3B2-C is the main conformation to occur ESIPT. Moreover, we get the different results of DH3B2 for the ESIPT mechanisms in comparison with the previous reports. We have optimized three isomers (DH3B2-A, DH3B2-B and DH3B2-C), and calculated absorption and fluorescence spectra, which agree well with the experimental data. Furthermore, we prove the hydrogen bond is enhanced in the S₁ state by comparing infrared vibrational spectra, the relevant bond length and bond angle. In our calculations, the results of the three levels of calculations (CAM-B3LYP/TZVP, B3LYP/TZVP and PBEPBE/TZVP) indicate that DH3B2-C is the most stable conformation, by compared the single point energy of three isomers. By constructed the potential energy surfaces (PESs), we find the converted relationship among the three isomers; DH3B2-C is the main conformation in which DH3B2 exists. Furthermore, combination with reduced density gradient (RDG) function, the hydrogen bond of DH3B2-C is stronger than that of DH3B2-A and DH3B2-B, which proves that DH3B2-C form is the most favorable form for ESIPT among the three isomers. Meanwhile, we have further investigated the ESIPT mechanisms of DH3B2, via constructing the potential energy curves (PECs). These results have shown that DH3B2-C is easier to ESIPT occur than DH3B2-A and DH3B2-B. Therefore, the proton receptors of the ESIPT are mainly the benzimidazole nitrogen atoms.

First-principles investigation of the double ESIPT process in a thiophene-based dye

Explanation of the experimental triple emission with theoretical tools requires advanced solvent models.

A theoretical study of the ESIPT mechanism of 3-hydroxyflavone derivatives: solvation effect and the importance of TICT for its dual fluorescence properties

As the dielectric constant decreases, the ESIPT reaction occurs more easily and TICT is good at emitting double fluorescence.

New insights into the sensing mechanism of a phosphonate pyrene chemosensor for TNT

As security needs have increased, mechanism investigation has become of high importance in the development of new sensitive and selective chemosensors for chemical explosives. This study details a theoretical investigation of the sensing mechanism of a new phosphonate pyrene chemosensor for trinitrotoluene (TNT), suggesting a different interaction mode between the probe and TNT from the one previously reported. The invalidity of the mechanism of binding TNT through intermolecular hydrogen bonds was proved using the Gibbs free energy profile and 1H NMR analysis. Frontier molecular orbitals (FMOs) analysis was used to show that photo-induced electron transfer (PET) is the underlying mechanism behind the luminescence quenching of the probe upon exposure to TNT, the rationality of which was further confirmed by the recording of a high charge transfer rate. We also found the existence of an energy level crossing between the local excited (LE) state and charge transfer (CT) state of a complex of the probe and TNT, which was confirmed using energy profile calculations along the linearly interpolated internal coordinate (LIIC) pathway.