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¹H NMR Signal Multiplicity: Splitting Patterns01:13

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When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
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Fluorescence and phosphorescence are essential phenomena in fields like analytical chemistry, biological imaging, and materials science, where they detect molecular properties and visualize cellular structures. Understanding the variables that influence these luminescent behaviors is crucial for maximizing accuracy and efficiency in their applications. These variables can broadly be grouped into chemical structure, solvent properties, and external conditions, each playing a distinct role in...
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Deleterious substances in aggregates can be detrimental to the quality and durability of concrete. These substances include organic impurities like loam, which interfere with cement hydration and are usually present in the sand. These prevent a good bond between aggregate and cement paste. Organic impurities can be detected using the colorimetric test, where the darkness of a solution after agitation indicates the level of organic content.
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Updated: Nov 27, 2025

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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Polymorphism-Dependent Enhanced Emission in Molecular Aggregates: J-Aggregate versus X-Aggregate.

Suqian Ma1,2, Yingjie Liu1, Jibo Zhang1

  • 1State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, China.

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|December 7, 2020
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This study introduces a new organic fluorescent molecule, BDFVA, with two crystal forms. These forms demonstrate enhanced light emission in solid states due to crystallization-induced emission enhancement (CIEE), showing potential for solid-state lasers.

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Area of Science:

  • Materials Science
  • Photophysics
  • Organic Chemistry

Background:

  • Solid-state photoluminescence of organic materials is strongly influenced by aggregation structures.
  • Understanding luminescence from J- and X-aggregates is crucial for designing efficient organic emitters.

Purpose of the Study:

  • To present an organic fluorescent molecule, 9,10-bis(2,2-di(4-fluorophenyl)vinyl)anthracene (BDFVA), as a model system for studying J- and X-aggregates.
  • To investigate the relationship between crystal polymorphism, aggregation structure, and photoluminescence properties.

Main Methods:

  • Synthesis and characterization of BDFVA.
  • Crystallographic analysis to determine aggregation structures (J- and X-aggregates).
  • Photophysical measurements including fluorescence quantum yield and amplified spontaneous emission (ASE).

Main Results:

  • BDFVA exhibits two crystal polymorphisms (G-phase and B-phase) corresponding to J- and X-aggregates.
  • Both crystal forms show crystallization-induced emission enhancement (CIEE) compared to dilute solutions.
  • The X-aggregate (B-phase) crystal demonstrates higher fluorescence efficiency (ΦF = 0.60) due to optically allowed split excited states.
  • Excellent amplified spontaneous emission (ASE) was observed in both crystal types.

Conclusions:

  • BDFVA serves as an effective molecular model for elucidating luminescence mechanisms in J- and X-aggregates.
  • The crossed molecular packing in X-aggregates leads to superior fluorescence efficiency.
  • The observed CIEE and ASE properties highlight the potential of BDFVA for applications in organic solid-state lasers.