Defects Cause Subgap Luminescence from a Crystalline Tetracene Derivative

Area of Science:

• Organic semiconductor physics
• Materials science
• Solid-state spectroscopy

Background:

• Organic semiconductors are key for next-generation electronics.
• Understanding sub-bandgap optical properties is crucial for device applications.
• 5,12-diphenyl tetracene (DPT) exhibits complex photophysical behavior.

Purpose of the Study:

• To elucidate the origin of light emission below the optical gap energy (E_o) in crystalline DPT.
• To identify the nature of electronic transitions responsible for sub-E_o emission.
• To investigate the role of structural defects in DPT's optoelectronic properties.

Main Methods:

• Steady-state and ultrafast nonlinear spectroscopies.
• Density functional theory (DFT) calculations.
• Analysis of vibrational coherence spectra and polarization dependence.

Main Results:

• Evidence for discrete electronic transitions below E_o in DPT.
• Identification of structural defect states as the source of sub-E_o emission.
• Tentative assignment of defect types based on polarization-dependent coherence spectra.

Conclusions:

• Structural defects significantly influence the optoelectronic properties of DPT.
• Sub-E_o emission is linked to midgap states arising from these defects.
• Fundamental insights into midgap states advance organic photonics and optoelectronics.