Activating the Fluorescence of a Ni(II) Complex by Energy Transfer

Area of Science:

• Surface Science
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Open-shell 3d metal complexes often exhibit quenched luminescence due to rapid intersystem crossing (ISC) and population of dark states.
• Efficient fluorescence from such complexes is crucial for developing new luminescent materials and devices.

Purpose of the Study:

• To demonstrate the activation of fluorescence in individual nickel phthalocyanine (NiPc) molecules.
• To investigate methods for overcoming the inherent luminescence quenching mechanisms in NiPc.

Main Methods:

• Utilized scanning tunneling microscopy (STM) to manipulate and probe individual NiPc molecules.
• Employed STM-induced luminescence, scanning tunneling spectroscopy, and photoluminescence experiments.
• Conducted time-dependent density functional theory (TD-DFT) calculations to understand electronic transitions.

Main Results:

• Achieved Q-band fluorescence from NiPc molecules via resonant energy transfer from adjacent metal phthalocyanines (MPc, M = Zn, Pd, Pt).
• Showed that resonant energy transfer excites NiPc without overcoming the activation barrier for intersystem crossing (ISC).
• Demonstrated that a designed local environment and directed excitation can prevent population of dark metal-centered states.

Conclusions:

• Successfully activated fluorescence in NiPc by circumventing the thermally activated population of dark states.
• This approach enables the use of abundant transition metal complexes as luminophores, avoiding reliance on precious metals like Pt or Ir.
• Highlights the potential for controlling molecular luminescence through precise environmental engineering and excitation pathways.