Organic Light-Emitting Diode Employing Metal-Free Organic Phosphor

Abstract

Metal-free organic phosphorescent materials are promising alternatives to the organometallic counterparts predominantly adopted in organic light-emitting diodes due to their low cost, chemical stability, and large molecular design window. However, only a few reports on OLED devices incorporating metal-free organic phosphors have been presented due to the lack of understanding on material properties, device physics, and device fabrication processes. Here, we report a tailor-designed novel fluorene-based organic phosphor with efficient spin–orbit coupling activated by bromine, aromatic carbonyl, and spiro-annulated phenyl moieties. Photoluminescence quantum yield of 24.0% was achieved when doped in optically inert amorphous polymer hosts. Effects of OLED host materials on the phosphor were investigated in terms of color purity, suppression of exciplex emission, and restraint of molecular motion. Bright green phosphorescence emission (1430 cd/m2 at 100 mA/cm2) was realized with 2.5% maximum external quantum efficiency at 1 mA/cm2.

Photoresponsive Luminescence Switching of Metal‐Free Organic Phosphors Doped Polymer Matrices

“…[22] In fact, photobleaching was substantially reduced when the aldehyde was replaced by trifluoroacetyl group, as demonstrated by our recently developed metal-free organic phosphor, BrPFL-TFK ( Figure S12, Supporting Information). [23] Figure 1. a) Chemical structures of Br6A, a metal-free organic phosphor, and a-PMMA. b) Images taken from the video recording 1 wt% Br6A doped a-PMMA (Br6A/a-PMMA) irradiated by a UV lamp (1.06 mW cm −2 ).…”

“…[ 22 ] In fact, photobleaching was substantially reduced when the aldehyde was replaced by trifluoroacetyl group, as demonstrated by our recently developed metal‐free organic phosphor, BrPFL‐TFK (Figure S12, Supporting Information). [ 23 ]…”

Heavy Atom Oriented Orbital Angular Momentum Manipulation in Metal-Free Organic Phosphors

“…A related, but less powerful method is to place heavy atoms adjacent to conventional El-Sayed rule satisfying moieties, so that they could participate in the ( , * ) -( , * ) type Δ . This design rationale employs halogen-containing POPs, 7,8 since halogens only has one available bonding site and could not create efficient Δ channels on their own. While the fused-ring motif of the present article appears to efficiently utilize the HAAM concept by connecting the heavy atom within the Δ -producing channel, heavy chalcogen atoms could also be placed in attachable pendent groups to create Δ channels, such as coupling them with ester or anhydride groups, or directly replace the oxygen in carbonyl with heavier chalcogens.…”

“…The El-Sayed rule 20 qualitatively elucidated the angular momentum conservation law, for example in a typical case the ( , * ) -( , * ) transition carries a change in orbital angular momentum (Δ ), but a ( , * ) -( , * ) is not expected to do the same. On the other hand, large Δ has been observed in other types of transitions 7,18 , even for ( , * ) -( , * ) transitions.…”

“…1 listed a few representative POPs with halogen or chalcogen heavy atoms: Br [5][6][7][8][9][10][11][12][13][14][15] , I 16,17 , or Se 18,19 . The El-Sayed rule explains the necessity of ( , * ) -( , * ) transitions in promoting SOC 20 , and the utilization of carbonyl [5][6][7][8][9][10][11][12][13] , heterocyclic rings [21][22][23] (e.g. triazine in DPhCzT 21 ), and other moieties having rich non-bonding electrons (e.g.…”