Organic light-emitting diodes (OLEDs) are a promising technology due to their lower manufacturing cost and ability to be fabricated on lightweight, flexible substrates. However, OLEDs have a theoretical efficiency of only 25% due to charges having a 75% chance of becoming triplet excitons upon injection. To overcome this limit, significant work has been carried out on systems which can undergo thermally activated delayed fluorescence (TADF), a process which allows triplet excitons to be promoted back to singlet states. However; a complete understanding of TADF in organic molecules remains unclear. Such information is critical for the design of new OLED devices that utilize TADF molecules. In this work, we use photoluminescence and time-resolved spectroscopy to study the influence that the local environment has on the excited state properties of NAI-DMAC, a molecule known to undergo TADF. PL measurements of NAI-DMAC in a polystyrene matrix reveal dispersive energy transfer to lower lying energy states present in the matrix. However, such transfer is absent in NAI-DMAC solutions. These results indicate energetically unfavorable conformations in the NAI-DMAC matrix that restrict NAI-DMAC reorientation, in a device this wider distribution of energetic states could lead to decreased color purity making the device unsuitable for display applications. These findings are important as they allow for a clearing understanding of what is occurring in the solid state and allow us to better assign the electronic states often used to determine singlet-triplet differences.

Investigating the influence the local environment has on thermally activated delayed fluorescence

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