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Steric Gating of Excited-State Channel: Controllable AIE/RTP Switching through Tuning π-Bond Twisting.

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Steric bulk controls excited-state pathways in π-conjugated molecules, enabling dynamic switching between aggregation-induced emission (AIE) and solution-phase fluorescence. This steric gating mechanism offers novel strategies for designing advanced AIE and RTP-active materials.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Photophysics

Background:

  • π-conjugated systems are crucial for optoelectronic applications.
  • Controlling excited-state dynamics in these systems remains a challenge.
  • Aggregation-induced emission (AIE) and room-temperature phosphorescence (RTP) are desirable properties for advanced materials.

Purpose of the Study:

  • To demonstrate steric control over excited-state channels in π-conjugated 1,1'-bibenzo[f]isoindolylidenes.
  • To achieve dynamic switching between aggregation-induced emission (AIE) and dilute/dual-state fluorescence.
  • To develop a novel strategy for designing advanced AIE and RTP-active molecules.

Main Methods:

  • Substituent-engineered C═C bond twisting to tune steric bulk (R²).
  • Variable-temperature Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopy to confirm biradicaloid isomerization.
  • Time-Dependent Density-Functional Theory (TD-DFT) analysis to validate the steric gating mechanism.

Main Results:

  • Tuning substituent bulkiness dynamically switches emission between AIE and solution-phase fluorescence.
  • π-twisting activates low-energy configuration interaction (CI) pathways for AIE generation.
  • Excessive bulkiness relocks molecular conformation, enabling solution-phase emission and controlling fluorescence/phosphorescence.

Conclusions:

  • Steric gating of biradicaloid isomerization channels provides precise control over excited-state pathways.
  • This mechanism allows for controllable fluorescence and phosphorescence by modulating π-twisting.
  • The demonstrated strategy offers a new avenue for designing sophisticated AIE and RTP-active organic materials.