Photophysical Properties of Dioxolane-Substituted Pentacene Derivatives Dispersed in Tris(quinolin-8-olato)aluminum(III)

Abstract

Two novel dioxolane-substituted pentacene derivatives, namely, 6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (TP-5) and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (EtTP-5), have been synthesized and spectroscopically characterized. Here, we examine the steady-state and time-resolved photoluminescence (PL) of solid-state composite films containing these pentacene derivatives dispersed in tris(quinolin-8-olato)aluminum(III) (Alq(3)). The films show narrow red emission and high absolute photoluminescence quantum yields (phi(PL) = 59% and 76% for films containing approximately 0.25 mol % TP-5 and EtTP-5, respectively). The Förster transfer radius for both guest-host systems is estimated to be approximately 33 A. The TP-5/Alq(3) thin films show a marked decrease in phi(PL) with increasing guest molecule concentrations, accompanied by dramatic changes in the PL spectra, suggesting that intermolecular interactions between pentacene molecules result in the formation of weakly radiative aggregates. In contrast, a lesser degree of fluorescence quenching is observed for EtTP-5/Alq(3) films. The measured fluorescence lifetimes of TP-5 and EtTP-5 are similar (approximately 18 ns) at low concentrations but deviate at higher concentrations as aggregation begins to play a role in the TP-5/Alq(3) films. The onset of aggregation in EtTP-5/Alq(3) films occurs at higher guest molecule concentrations (>1.00 mol %). The addition of ethyl groups on the terminal dioxolane rings leads to an increase in the intermolecular spacing in the solid, thereby reducing the tendency for pi-pi molecular stacking and aggregation.

High-Performance Organic Light-Emitting Diodes Based on Dioxolane-Substituted Pentacene Derivatives

“…0.25 to 2.0 mol %, similar to those used in the films prepared for the aforementioned time-resolved PL Study. [30] The devices reveal bright red emission with EL characteristics that compare favorably to other OLEDs featuring pentacene derivatives as the active emitting center. [25,26] As seen in Figure 1, red emission from the guest pentacene derivatives dominates the EL spectra, although a minor contribution from the Alq 3 host persists at k max ≈ 535 nm.…”

“…[35] We have recently demonstrated that Alq 3 is an excellent host for dioxolane-substituted pentacene derivatives. [30] The well-resolved overlap between the Alq 3 host emission spectrum and pentacene guest absorption spectrum yields an estimated Förster transfer radius of R 0 = 33 Å for both TP-5:Alq 3 and EtTP-5:Alq 3 composite solid film systems. High energy-transfer efficiencies (g ET ≥ 90 %) are predicted at relatively low guest-molecule concentrations (ca.…”

“…They exhibit sharp red emission in toluene solution (k max = 625-630 nm, full width at half maximum, FWHM = 21 nm) with up to a fourfold increase in PL quantum yield (f PL = 72.0 % for EtTP-5) [30] relative to 6,13-diaryl pentacene derivatives. [26] TP-5 and EtTP-5 have also shown high-efficiency emission in the solid state; when dispersed in Alq 3 , these guest-host composite films show maximum absolute PL quantum yields of 59 and 76 %, respectively.…”

“…[26] TP-5 and EtTP-5 have also shown high-efficiency emission in the solid state; when dispersed in Alq 3 , these guest-host composite films show maximum absolute PL quantum yields of 59 and 76 %, respectively. [30] Herein, we detail the fabrication of OLEDs based on these guest-host molecular systems and examine the device performance. The OLED devices show bright red emission with excellent current density-voltage-luminance (J-V-L) characteristics and high external EL quantum yields.…”

Conjugated Organosilicon Materials for Organic Electronics and Photonics

“…10). TIPS-5AC-DO used as a guest emitter in the tris(8-quinolinolato) aluminum(III) complex (Alq 3 ) and 4, 4 -bis[N-1-naphthyl-Nphenylamino]-biphenyl (NPD) host matrices (common hole-transport materials used in OLEDs) showed efficient energy transfer and bright red photoemission at very low concentrations (less than 0.5 mol%) [46]. However, a higher dopant concentration led to aggregate emissions that motivated the synthesis of the more bulky derivative TIPS-5AC-DO-ET (functionalized with ethyl groups at the dioxolane ring).…”