Unlocking Brightness in Inverted Singlet-Triplet Systems via J-Aggregate Formation

Area of Science:

• Organic Optoelectronics
• Photophysics
• Materials Science

Background:

• Inverted Singlet-Triplet (INVEST) emitters offer an alternative to traditional Thermally Activated Delayed Fluorescence (TADF) systems.
• A major obstacle for INVEST emitters is their low radiative efficiency, caused by the weak oscillator strength of the S0 → S1 transition.

Purpose of the Study:

• To investigate cyclazine derivatives as potential INVEST emitters.
• To demonstrate how dimerization can enhance the oscillator strength and radiative efficiency of INVEST emitters.

Main Methods:

• Computational investigation of cyclazine derivatives using LR-TDDFT and DLPNO-STEOM-CCSD.
• Systematic computation of excited-state properties for monomers and J- and H-aggregate dimers.

Main Results:

• J-aggregate dimers exhibit significantly enhanced oscillator strength (f_osc) compared to H-aggregates and monomers.
• The S1 state in J-aggregate dimers shows a mixed locally excited character, unlike in H-aggregates.
• Dimerization effectively overcomes the intrinsic oscillator strength bottleneck of INVEST emitters.

Conclusions:

• Dimerization of cyclazine derivatives is a viable strategy to boost radiative efficiency in INVEST emitters.
• This aggregation-induced enhancement provides a general design principle for developing bright INVEST emitters for organic optoelectronics.