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Pyrazole-Substituted 3-Hydroxychromones: Conformation-Dependent Proton-Transfer Isomerization.

Hao-Cheng Tsai1, Yan-Ding Lin1, Hao-Ting Qu1

  • 1Department of Chemistry, National Taiwan University, Taipei, Taiwan.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|July 9, 2026
PubMed
Summary
This summary is machine-generated.

We developed a new organic dye, PRA-3HC, for amplified spontaneous emission (ASE) and lasing. While it shows efficient emission, its photostability is limited, but modifications offer improved performance for photonic materials.

Keywords:
3‐hydroxyflavone derivativesamplified spontaneous emissionexcited state intramolecular proton transferground state tautomerphotodegradation

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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions

Published on: July 17, 2020

Area of Science:

  • Organic Photophysics
  • Materials Science
  • Spectroscopy

Background:

  • Organic dyes with large Stokes-shifted emission and high photostability are vital for amplified spontaneous emission (ASE) and lasing.
  • 3-hydroxychromone (3HC) derivatives are promising due to excited-state intramolecular proton transfer (ESIPT) causing large Stokes shifts, but their photostability is a limitation.

Purpose of the Study:

  • To synthesize and characterize a novel 3HC derivative, PRA-3HC, incorporating a pyrazole unit to enhance structural rigidity via an additional intramolecular hydrogen bond.
  • To investigate the influence of pyrazole substitution and hydrogen bonding on the photophysical properties and photostability of 3HC derivatives.
  • To explore the role of ground-state tautomerization in governing the performance of these ESIPT photonic materials.

Main Methods:

  • Synthesis of 3-hydroxy-2-(1H-pyrazol-3(5)-yl)-4H-chromen-4-one (PRA-3HC) and its N1-Me and N2-Me derivatives.
  • Spectroscopic analysis (absorption, fluorescence) in solvents of varying polarity.
  • Nuclear Magnetic Resonance (NMR) spectroscopy.
  • Evaluation of amplified spontaneous emission (ASE) activity and photostability under operating conditions.

Main Results:

  • PRA-3HC exhibits efficient ESIPT emission (65%-66% quantum yield) in low-polarity solvents, adopting the N1-H(a) tautomer.
  • Increased solvent polarity shifts the equilibrium to the non-emissive N2-H(b) isomer, explaining spectral mismatches.
  • Despite strong ASE activity, PRA-3HC shows rapid photobleaching within 3 minutes, while N1-Me and N2-Me derivatives demonstrate significantly improved photostability.

Conclusions:

  • Ground-state tautomerization critically influences the photophysical properties and photostability of pyrazole-substituted 3HCs.
  • The pyrazole unit's hydrogen bonding impacts structural rigidity and ESIPT efficiency.
  • Findings provide crucial insights for designing robust, high-performance ESIPT photonic materials for ASE and lasing applications.