[en] Acridone (acceptor) and naphthylamine (donor) based Donor-Acceptor-Donor (D-A-D) compound (1) was synthesised, characterised and its thermally-activated delayed fluorescence (TADF) properties were studied in detail. Compound 1 is fluorescent and emits in the green region (550 nm). The energy gap between the ground and the lowest excited singlet (S₁) state is estimated to be 2.55 eV. The energy gap between the CT singlet and triplet states (∆E_ST) was found to be ~0.3 eV. Small ∆E_S1-T1 is one of the important criteria for TADF to take place in a molecule and thus detailed photophysics has been studied. Transient lifetime measurements showed an increase in the fluorescence lifetime (τ) on purging with N₂, as compared with that in air-saturated solution, indicating the involvement of the triplet state in emission. Emission at 550 nm was also observed with a delay of 100 µs which corresponded to the delayed fluorescence in 1. The lifetime of TADF was found to be 176 µs. Applications of TADF materials in organic light-emitting devices (OLEDs) has gotten attention as TADF materials utilise the triplet excitons which helps in increasing internal quantum efficiency of device. Air-saturated based on 1 were fabricated and their intensity was found to be nearly as high as 17,000 Cd/m² at 25 mA/cm² which was comparable to many of the known TADF emitters.

Graphic abstract

Acridone-amine derivatives was synthesized and its photophysical properties were carried out to establish TADF. It was also used in fabrication of OLEDs. <Image>.