Promoting Intersystem Crossing of a Fluorescent Molecule via Single Functional Group Modification

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Pure light-atom organic phosphorescent molecules are attractive due to cost, flexibility, and environmental friendliness.
• Developing these materials is hindered by intrinsically small spin-orbit couplings.
• Achieving efficient phosphorescence requires balancing intersystem crossing (ISC) and fluorescence rates.

Purpose of the Study:

• To design and synthesize pure light-atom organic phosphorescent molecules with improved efficiency.
• To investigate the impact of chemical modifications on ISC and fluorescence rates.
• To establish a strategy for creating novel organic phosphorescent materials.

Main Methods:

• Utilized N-substituted naphthalimides as a prototype molecular scaffold.
• Applied chemical modifications using various electrophilic and nucleophilic functional groups.
• Analyzed changes in intersystem crossing (ISC) and fluorescence rates.

Main Results:

• Electron-donating groups effectively suppressed fluorescence, promoting efficient ISC to the triplet state.
• Electron-withdrawing groups did not significantly alter the luminescent properties of the parent molecules.
• Observed a correlation between ISC/fluorescence rates and the nature of the lowest singlet state (localized vs. charge-transfer excitation).

Conclusions:

• Chemical modification of N-substituted naphthalimides offers a viable strategy for tuning ISC and fluorescence.
• The transition from localized to charge-transfer excitation in the singlet state is key to efficient phosphorescence.
• This approach provides a new pathway for designing high-performance pure light-atom organic phosphorescent materials for diverse applications.