Guest Emission Processes in Doped Organic Light-Emitting Diodes:  Use of Phthalocyanine and Naphthalocyanine Near-IR Dopants

Abstract

A series of near-IR emitting organic light-emitting diodes (OLEDs) have been prepared using poly(vinylcarbazole) (PVK) as the hole transport polymer, aluminum quinolate (Alq3) or a sulfonamide derivative (Al(qs)3) as the host dye (H), and phthalocyanine (Pc) or naphthalocyanine (NPc) dopants as guest dyes (G). The separation of the emission spectrum of the guest dye from that of the host dye allows for independent assessment of their relative efficiencies and correlation of these efficiencies with their tendencies toward charge capture and recombination reminiscent of solution electrogenerated chemiluminescent reactions. Although the absorbance spectra of the guest dyes are significantly separated from the emission spectra of the host dyes, the high molar absorptivities of the Pc and NPc dopants lead to Förster radii and relative energy-transfer (ET) efficiencies comparable to values previously obtained for quinacridone or rubrene dopants, which have been used to create intense green or yellow emission in Alq3-based OLEDs. We show that hole capture by the guest dye from oxidized PVK, PVK+•/G → PVK/G+•, followed by cross-reactions, Alq3 -•(Al(qs)3 -•)/G+• → Alq3(Al(qs)3)/G*, can be an important charge-trapping (CT), light-producing pathway at sufficiently high concentrations of the guest dye. Relative efficiencies of Pc* or NPc* emission in these single-layer devices increased exponentially with the electrochemically predicted excess free energy for the oxidation of G to form G+• by PVK+•.

Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions

“…They can act as spectroscopic sensitizers deposited on semiconductor electrodes [169][170][171][172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187][188] and can have applications in solar energy conversion devices. The colour of phthalocyanines is modified when they undergo oxidation state changes involving the ligand and this can have applications in electrochromic devices [189][190][191].…”

Nanosecond nonlinear optical limiting properties of new trinuclear lanthanide phthalocyanines in solution and as thin films

“…These applications include as molecular conductors and semiconductors [2], non-linear optical (NLO) materials [3], dyes and pigments [4], light-emitting diodes [5], photoconductors in laser printers [6], photosensitizers in photodynamic therapy [7], electrochromic materials [8,9] and components of organic photovoltaic cells [10]. Lanthanide phthalocyanines in particular have been found to exhibit NLO behaviour [11,12].…”

Organic/Organic′ Heterojunctions: Organic Light Emitting Diodes and Organic Photovoltaic Devices

“…HOMO and LUMO energy levels have often been estimated from solution electrochemical experiments, where one-electron oxidation and reduction potentials are used to infer differences between HOMO and LUMO levels in condensed phase molecular thin films. [19,34,68,69,101,102,120] These measurements are referenced to vacuum, assuming the potential of a reference electrode, like the normal hydrogen electrode (NHE % À4.5eV) is known, and can be extrapolated to the electrolyte solutions where the measurements were made. [184,185] Account must also be taken for differences in stabilization of the oxidized and reduced molecular states…”