High-color-purity and efficient solution-processable blue phosphorescent light-emitting diodes with Pt(ii) complexes featuring ³ππ* transitions

Abstract

A series of Pt(ii) complexes with narrow emission spectra were systematically investigated and Pt(ppzOczpy-4m), rationally designed with predominantly 3LC(3ππ*) character in T1, was fabricated into efficient blue OLEDs via a solution process.

Tetradentate Pt(II) Complexes for Spectrum‐Stable Deep‐Blue and White Electroluminescence

“…The characteristic emission demonstrate that 3 MLCT states could be enhanced by neighboring molecule, leading to broad emission in T 1 →S 0 transition. [ 24 ] Emission lifetimes were measured at peak wavelengths in various concentrations by single‐exponential fit of the decay curves, affirming single excited‐state deactivation of T 1 →S 0 process (Figure S5, Supporting Information). In frozen 2‐MeTHF at 77 K, the emission spectra of Pt(pzpyOczpy‐ i Pr) and Pt(pzpyOczpy‐mesi) show the similar vibronic structure but 5–6 nm bathochromic shifting with when compared to those of Pt(ppzOczpy) series of complexes, indicating that T 1 →S 0 transitions are still dominated by ligand‐centered ( 3 LC) triplet state on carbazole but configurationally enhanced with the perturbation of regional substates.…”

“…The bathochromic‐shift and broader EL spectra can be attributed to the positive solvatochromic effect of the 3 LC dominated transition as well as an inhomogeneous broadening effect of the admixing T 1 states. [ 22,24 ] White light devices were fabricated by involving the emissive layers of 50 wt% complex doped into mCPCN, and came to the light with a lower turn‐on voltage at 3.0 V. (Table 2) As disclosed in their PL transitions, monomeric emission by enhanced 3 π py *→dπ and 3 π pzpy *→dπ transitions are accompanied with excimeric emissions under high concentration, thereby giving broad EL spectra with dissimilar FWHMs of 120 and 100 nm for the devices of Pt(pzpyOczpy‐ i Pr) and Pt(pzpyOczpy‐mesi), respectively (Figure 6a). The device of Pt(pzpyOczpy‐ i Pr) achieves better maximum CE, PE, and EQE at 57.5 cd m −2 , 60.2 lm W −1 , and 18%, respectively, and remains with the values of 40.8 cd m −2 , 27.9 lm W −1 , and 12.7% at a luminance of 1000 cd m −2 (Table 2).…”

“…[ 20–23 ] Furthermore, due to their environment‐sensitive property in the lowest triplet excited state (T 1 ), the emission spectra of the complexes are manageable according to certain circumstance. [ 24 ] Bearing in mind the nature of the Pt(II) complexes, we infer it is possible to tune the emission from narrow blue to broad white via triplet managing, [ 22 ] which is concurrently challenging in molecular design and desirable in display and lighting applications.…”

“…[ 42 ] Here, we report two highly emissive tetradentate Pt(II) complexes, Pt(pzpyOczpy‐ i Pr) and Pt(pzpyOczpy‐mesi), showing extraordinary tunable but color stable emission from deep blue to white. Owing to the increased 3 MLCT character in T 1 at high concentration, [ 24 ] the emissions derived from multi‐substates expand from narrow blue to broad white, different from the simple imposing of dual emissions. Pacing with the expanding, the full width at half‐maximums (FWHMs) of Pt(pzpyOczpy‐ i Pr) and Pt(pzpyOczpy‐mesi) are adjustable from 40 to 149 nm and 43 to 152 nm, respectively.…”

“…The PLQYs and radiation rates descend in a third value, suggesting that nonradiative decay may rise from long‐range intermolecular coupling and the restriction of molecular fluctuation. [ 24,45 ] As the doping concentration increases, the emission spectra are slightly red‐shifted in several nanometers, but change significantly in their profiles extending to the longer wavelength ( Figure a,b). This can be explained by the improvement of dipole‐dipole interaction when the molecules get closer, where enhanced 3 MLCT in hyper admixed T 1 states broaden the monomeric emission and the successive interactions of intermolecular π‐stacking increase the excimeric emission [ 21,24 ] (Figure S6, Supporting Information).…”