The Sensing and Reacting Mechanisms of a Fluorescent Probe for Formaldehyde: A Detailed Theoretical Exploration

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Abstract
Formaldehyde, a significant signal molecule in biological systems, is considered as many physiological processes and pathological diseases. Up to now, a number of fluorescent probes, crafted from naphthalene amide-hydrazine scaffolds, have been designed and synthesized for the purpose of formaldehyde detection. These probes are based on the principles of photoinduced electron transfer (PET) and twisted intramolecular charge transfer (TICT). In this paper, we employed a theoretical method to undertake a comparative analysis of the sensing mechanisms, photophysical characteristics, and reaction mechanism of Na-FA (6-hydrazineyl-2-propyl-1H-benzo[de]isoquinoline-1,3(2H)-dione) probe in aqueous environments. This method integrates the polarizable continuum model (PCM), time-dependent density functional theory (TD-DFT), and the thermal vibration correlation function formalism (TVCF) to provide a comprehensive understanding of the probe’s properties and behaviors. Our results indicated that the weak emission of Na-FA owes to the TICT and non-radiative dissipation, conversely, PET has little effect on it. In contrast, the bright emission, exhibited by the reaction product NZ (6-(2-methylenehydrazineyl)-2-propyl-1H-benzo[de]isoquinoline-1,3(2H)-dione) of probe molecule Na-FA and formaldehyde, can be attributed to the more rapid radiative transitions and relatively slower non-radiative transitions, and there is no PET involved. In addition, we found NZ possesses a greater two-photon absorption (TPA) cross section in the near infrared region compared with that of Na-FA molecule, which determines its application in two-photon absorption detection in organisms. The reaction mechanism of Na-FA and formaldehyde producing NZ has been investigated as well, according to the potential energy profile, we discovered that path B corresponds to a lower activation energy with the aid of ion participation, therefore, path B is a more favorable reaction pathway. At last, we predicted the one-photon and two-photon properties of thiol-substituted naphthalimide, and the calculated results indicated that this compound has excellent potential as a two-photon fluorescent probe.
Funding Information
  • Henan Provincial Science and Technology Research Project (24JRRE001)
  • Gansu Longyuan Talent Key Project (2022RCXM087)
  • Gansu Province Higher Education Innovation Fund Project (2021B-201)
  • Gansu Province University Young Doctor Support Project (2023QB-009)
  • Qinzhou District of Tianshui City Science and Technology Program (2024-SHFZG-6625)
  • 2024 Medical Special Project of Tianshui Normal University (YXZ2024-02)
  • Postgraduate Innovation Project of Tianshui Normal University (TCXM2534)
  • Key Subject of Theoretical Calculation in Tianshui Normal University, Key Laboratory for New Molecule Materials Design and Function of Gansu Universities

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