Sterically protected π-electron systems for efficient solid-state photon upconversion.

Area of Science:

• Materials Science
• Photochemistry
• Organic Electronics

Background:

• Developing solid-state photon upconversion (UC) systems is challenging due to the difficulty in achieving high fluorescence quantum yield and rapid triplet exciton diffusion simultaneously.
• Precise control over chromophore interactions and suppression of singlet/triplet excited state quenching are crucial for efficient UC.

Purpose of the Study:

• To develop a solid-state visible-to-ultraviolet photon upconversion system driven by low-intensity light.
• To identify optimal molecular structures for efficient photon upconversion in both solution and solid states.

Main Methods:

• Synthesis and investigation of dihydroindeno[2,1-a]indene derivatives functionalized with alkyl chains.
• Characterization of photophysical properties including fluorescence quantum yield, triplet lifetime, and triplet diffusion.
• Evaluation of photon upconversion quantum yield and threshold excitation intensity in solution and crystalline states.

Main Results:

• Identified an optimal dihydroindeno[2,1-a]indene derivative exhibiting the highest photon upconversion quantum yield.
• Achieved an absolute photon upconversion quantum yield of 1.9% in the solid-state system.
• Demonstrated a low threshold excitation intensity of 1.2 mW cm⁻² for the solid-state system.

Conclusions:

• The developed dihydroindeno[2,1-a]indene derivatives effectively meet the requirements for efficient solid-state photon upconversion.
• The solid-state system shows robustness against crystalline defects, maintaining high photoluminescence quantum yield and efficient triplet dynamics.
• This work presents a promising approach for low-intensity light-driven solid-state photon upconversion.