Doublet Emitters Derived from Stable Carbenes for Potential OLED Applications
Date
2020-05
Authors
Harmon, Gabrielle
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Abstract
Organic light emitting diodes (OLEDs) typically exhibit low quantum efficiencies (~19%) due to quantum mechanical limitations and spin statistics. In traditional OLEDs, the emitting excitons are either singlet (25%) or triplet (75%) spin states. Because decay from triplet states is spin forbidden, the internal quantum efficiency of fluorescent devices is limited to a theoretical maximum of 25%. To circumvent this problem, modern OLEDs rely on triplet, phosphorescent emitters, that require the incorporation of often expensive heavy atoms to facilitate intersystem crossing between the singlet and triplet excited states, thus increasing triplet emission. In contrast to the widely explored triplet emitters, this thesis will describe our recent efforts to prepare cationic and neutral doublet emitters derived from carbenes and triarylmethyl- or triarylboryl-centered radicals, respectively. In principle, doublet emitters have theoretical quantum efficiencies of up to 100%, making them ideal
candidates for next-generation light-emitting devices. Carbenes will be incorporated into the triarylmethyl- and triaryl boryl- compounds in order to change the emission color as well as stabilize the radical.
A series of cationic doublet emitters were synthesized and one (CAAC-TPFM radical) was layered onto a device. This device was found to be very inefficient, possibly due to anionic emission dampening.
A series of neutral doublet emitters were attempted with one doublet emitter (CAAC-triaryl boryl radical) being layered onto a device. This OLED device was tested for efficiency and found to be subpar due to degradation; however, carbenes were found to be successful in changing the emission colors of each molecule. Colors that were recorded were orange, yellow, green, and blue.
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Keywords
Carbenes, OLEDs
Citation
Harmon, G. E. (2020). <i>Doublet emitters derived from stable carbenes for potential OLED applications</i> (Unpublished thesis). Texas State University, San Marcos, Texas.