Effects of Intermolecular Hydrogen Bonding and Solvation on Enol–Keto Tautomerism and Photophysics of Azomethine–BODIPY Dyads

Abstract

Boron–dipyrromethene derivatives (BODIPYs) are a category of molecules with excellent photophysical properties and can be applied to various fields. This work investigates the fluorescent properties of two azomethine–BODIPY dyads in different solvents based on the time-dependent density functional theory (TD-DFT) method. The potential energy curves (PECs) show that the polar protic solvent and the enhanced π-conjugation effect can lower the proton-transfer (PT) barriers, causing the main configuration of NA-BODIPY in methanol to be the keto form, while the main configuration of NA-BODIPY in toluene and SA-BODIPY in methanol and toluene is the enol form. The keto forms of the two compounds possess the twisted intramolecular charge transfer (TICT) decay pathway in the excited state identified by the optimized twisted configurations and the appropriate barriers of the TICT process, whereas the twisted configurations of the enol forms are nonexistent. TICT successfully competes with excited-state proton transfer (ESIPT) of the keto form, which leads to the fluorescence quenching of NA-BODIPY in methanol. This work provides new ideas for the influence of enol–keto tautomerism and the competitiveness of TICT and ESIPT on the photophysical properties of BODIPYs and is expected to provide guidance for the design of new BODIPY functional molecules.

Effects of Twisted Intramolecular Charge Transfer Behavior on Excited-State Intramolecular Proton Transfer Reactions of Methyl Benzoate Derivatives in Water Solution

“…Thus, the ESIPT process of PDASE produced an extremely unstable ketone structure and returned to the initial state; that is to say, the occurrence of ESIPT was hindered. In addition, since the CT state was involved, the results of LR (linear response)-TDDFT/6-311G*/B3LYP-D3 need to be verified, − so we also used LR-TDDFT/6-311G*/CAM-B3LYP-D3 theory to calculate the spectral values and reaction energy barrier, and the energy barrier values calculated by this method again verified our conclusions (seen in Tables S2 and S3). Moreover, we also performed IRC analyses of the transition states by the Berny method, as shown in Figure .…”

ESIPT‐based AIE luminogens: Design strategies, applications, and mechanisms

“…Moreover, extensive theoretical studies have also been performed to unravel the sensing mechanisms of ESIPT‐based fluorophores, and reveal the effects of pH, temperature, substitutes, solvents, and intermolecular hydrogen bonding on the ESIPT process. [ 19–24 ]…”

“…Moreover, extensive theoretical studies have also been performed to unravel the sensing mechanisms of ESIPT-based fluorophores, and reveal the effects of pH, temperature, substitutes, solvents, and intermolecular hydrogen bonding on the ESIPT process. [19][20][21][22][23][24] Conventional organic fluorophores may suffer from aggregation-caused quenching (ACQ) owing to the strong intermolecular π-π stacking or formation of excimers, limiting their applications in living cells where high concentration in aqueous medium is required and in optoelectronic devices where the materials need to be worked in the aggregated-or solid-state. The aggregation-induced emission (AIE) is an opposite phenomenon of ACQ and was first reported by Tang et al in 2001.…”

Unraveling the Mechanism of ACQ-to-AIE Transformation of Fluorescein Derivatives

“…The related results under the LR solvation model are given in Figure S1. The energy of the n π* state is overestimated with the LR solvation model because the n π* state transition possesses charge transfer characteristics. − , Therefore, the effectiveness of the dark state quenching pathway has not been demonstrated under the LR solvation model. To prove the reliability of the calculation results of the CAM-B3LYP functional, we calculated the energy of the dark state and bright state with LR/cLR solvation models by using different functionals and ADC(2) method as shown in Table S1.…”