# Interplay of Aggregation-Induced Enhanced Emission and Thermally Activated Delayed Fluorescence in Asymmetric Fluorenyl–Benzothiadiazole Derivatives

## TL;DR

This paper explores how combining two fluorescence mechanisms improves light emission in organic materials, leading to better performance in devices like OLEDs.

## Contribution

The study introduces new fluorenyl–benzothiadiazole derivatives that combine AIEE and TADF for enhanced solid-state emission.

## Key findings

- FL-BTD-OAr and FL-BTD-IDB show aggregation-induced enhanced emission with higher quantum yields in the solid state.
- FL-BTD-IDB exhibits delayed emission and improved luminescence under vacuum, consistent with TADF behavior.
- OLEDs using FL-BTD-IDB achieve high brightness and efficiency due to the combined AIEE and TADF effects.

## Abstract

Combining thermally activated delayed fluorescence (TADF)
with
aggregation-induced enhanced emission (AIEE) provides an effective
strategy to improve solid-state emission in organic materials. Here,
we design four fluorenyl–benzothiadiazole (FL-BTD) derivatives
bearing additional donor groups, aryloxy (−OAr), aryl (−Ar),
iminodibenzyl (−IDB), and phenoxazine (−PXZ), to investigate
how molecular structure influences their photophysical properties.
FL-BTD-OAr and FL-BTD-IDB display AIEE, with quantum yields that are
significantly higher in the solid state (0.70 and 0.30, respectively)
than in solution. FL-BTD-IDB also exhibits delayed emission (t
d = 1.03 μs) and enhanced luminescence
under vacuum compared to an O2 atmosphere, consistent with
TADF. Organic light-emitting diodes (OLEDs) fabricated with these
materials show green emission (FL-BTD-Ar and FL-BTD-OAr) or orange
emission (FL-BTD-IDB). Device performance trends closely follow the
solid-state photophysics. FL-BTD-Ar, subject to partial aggregation
quenching, delivers the weakest performance, whereas FL-BTD-OAr benefits
from AIEE, resulting in improved brightness and efficiency. The best-performing
device is based on FL-BTD-IDB, which combines AIEE and TADF to achieve
high brightness (15,000 cd m–2) and higher external
quantum efficiency (EQE) compared to the analogs.