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Cross-conjugated diaryl thieno-[3,4-b]thiophenes (TT) exhibit tunable photoswitching. Their photocyclization dynamics are controlled by substituent electronic interactions, influencing polymer electronic properties.

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Area of Science:

  • Materials Science
  • Organic Chemistry
  • Photochemistry

Background:

  • Diaryl thieno-[3,4-b]thiophenes (TT) are photoswitchable molecules designed for π-conjugated polymers.
  • Their photoinduced cyclization/cycloreversion allows manipulation of polymer electronic properties.

Purpose of the Study:

  • Investigate how cross-conjugating the central TT moiety affects photocyclization dynamics.
  • Correlate substituent electronic interaction strength with photoswitching behavior.

Main Methods:

  • Transient absorption spectroscopy (TAS) across various timescales (ultrafast to microsecond).
  • Synthesis of TT derivatives with varying electron-rich substituents.
  • Steady-state photoconversion experiments.

Main Results:

  • Ultrafast TAS (<1-10 ps) shows rapid dynamics consistent with photocyclization for switchable TT derivatives.
  • Slower dynamics (~100 ps) inconsistent with cyclization observed for non-switchable TT derivatives with strong substituent interactions.
  • Microsecond TAS confirms photocyclization in switchable compounds and metastable triplet state formation in non-switchable compounds.

Conclusions:

  • The balance between photocyclization and triplet state formation is sensitive to substituent interaction strength.
  • Strong interactions delocalize LUMO over the TT backbone, hindering photoswitching.
  • Structural control by weakening π-conjugation across the backbone can tune deactivation pathways.