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Updated: Jul 10, 2026
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Hydrogen-/halogen-bond switching enables exciton switching for color and singlet-triplet dynamics tuning in pyridine
WenXin Wu1, Ming Xue1, TaoTao Gao1
1State Key Laboratory of Petroleum Pollution Control, CNPC Research Institute of Safety and Environmental Technology Co., Ltd., Beijing 102206, China.
Abstract:
Regulating solid-state emission without altering molecular backbones remains challenging because excited-state pathways are highly packing-dependent. Here we show that supramolecular cocrystallization can reprogram the dominant excitation character of a pyridine N-oxide luminophore (NyPO) by selectively engaging hydrogen bonding versus halogen bonding at the same acceptor site. Under identical 365 nm excitation, the hydrogen-bonded NyPO·H2O crystal exhibits blue emission at approximately 460 nm, whereas the halogen-bonded NyPO·TITFB·DCM cocrystal shows red-shifted green emission at approximately 539 nm, accompanied by accelerated prompt singlet decay (τavg decreased from 8.69 to 1.20 ns) and the emergence of a minor long-lived delayed component (801 μs, 6.87%). Natural transition orbitals and charge density difference analyses suggest an exciton-type switch from a homomolecular intermolecular charge-transfer (homo-CT) excitation to a donor-acceptor intermolecular charge-transfer (CT) excitation from NyPO to TITFB (hetero-CT), with a markedly stabilized low-energy S1 (the calculated S1 energy decreased from 3.296 to 2.494 eV) and reduced oscillator strength. Spin-orbit coupling calculations further suggest intersystem crossing pathway reorganization in the cocrystal. These results demonstrate cocrystallization as a practical strategy to regulate emission color and excited-state dynamics via interaction-programmed exciton switching.
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