Conformational disorder enabled emission phenomena in heavily doped TADF films. Issue 1 (10th December 2021)

• Record Type: Journal Article
• Authors: Serevičius, Tomas; Skaisgiris, Rokas; Gudeika, Dalius; Kazlauskas, Karolis; Juršėnas, Saulius
• Is Part Of: Physical chemistry chemical physics. Volume 24:Issue 1(2021)
• Page Start: 313
• Page End: 320
• Publication Date: 2021-12-10
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp04905d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Increasing the doping load of a TADF emitter in a solid host enables triplet migration and subsequent quenching of long-lived delayed emission. This enables an emission peak shift and an rISC rate increase, though at the cost of a lowered emission yield. Abstract : Thermally activated delayed fluorescence (TADF) compounds doped in solid hosts are prone to undergo solvation effects, similar to those in the solution state. Emission peak shifts and changes in emission decay rates usually follow solid-state solvation (SSS). However, here we show that typical SSS behavior in heavily doped TADF films could be of a completely different origin, mistakenly attributed to SSS. Typically, increasing the doping load was found to redshift the emission peak wavelength and enhance the rISC rate. However, more in-depth analysis revealed that SSS actually is negligible and both phenomena are caused by the specific behavior of delayed emission. Increasing the concentration of the TADF compound was shown to enhance the concentration quenching of long-lived delayed fluorescence from conformer states with the largest singlet energy, eventually leading to a gradual redshift of the delayed emission peak wavelength. Concomitantly, the loss of long-lived delayed fluorescence entailed reverse intersystem crossing rate enhancement, though the rate-governing singlet–triplet energy gap was gradually increasing. The observed phenomena are highly unwanted, burdening molecular structure and OLED performance optimization.