Marc Lepeltier

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

Summary In the present paper, the photoredox catalysis is presented as a unique approach in the field of photoinitiators of polymerization. The principal photocatalysts already reported as well as the typical oxidation and reduction agents used in both reductive or oxidative cycles are gathered. The chemical mechanisms associated with various systems are also given. As compared to classical iridium-based photocatalysts which are mainly active upon blue light irradiation, a new photocatalyst Ir(piq)2(tmd) (also known as bis(1-phenylisoquinolinato-N,C 2’)iridium(2,2,6,6-tetramethyl-3,5-heptanedionate) is also proposed as an example of green light photocatalyst (toward the long wavelength irradiation). The chemical mechanisms associated with Ir(piq)2(tmd) are investigated by ESR spin-trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments.

Photoredox catalysis using a new iridium complex as an efficient toolbox for radical, cationic and controlled polymerizations under soft blue to green lights

A new iridium complex (nIr) was designed and investigated as a photoinitiator catalyst for radical and cationic polymerizations upon very soft irradiations (lights ranging from 457 to 532 nm). A ring-opening polymerization (ROP) of an epoxy monomer was easily promoted through the interaction between nIr and an iodonium salt (Iod) upon light. The addition of N-vinylcarbazole (NVK) enhances the performance. In radical polymerization, nIr can be efficient in combination with phenacyl bromide (PBr) and optionally an amine: these photoinitiating systems work according to an original oxidative cycle and a regeneration of nIr is observed. A control of the methyl methacrylate polymerization (conducted under a 462 nm light) with 1.2–1.6 polydispersity indexes was displayed. Surface modifications by direct laser write was also easily carried out for the first time through surface re-initiation experiments, i.e. the dormant species being reactivated by light in the presence of nIr; the polymer surfaces were analyzed by XPS. The chemical mechanisms were examined through laser flash photolysis, NMR, ESR and size exclusion chromatography experiments.

Unprecedented combination of regioselective hydrodefluorination and ligand exchange reaction during the syntheses of tris-cyclometalated iridium(III) complexes

The first reported combination of regioselective hydro-defluorination and a ligand exchange reaction during the syntheses of neutral iridium(III) complexes is presented. Surprisingly, loss of one fluorine atom per ligand combined with a complete ligand exchange reaction on the transition metal were jointly observed during a bridge-splitting and substitution reaction of two different dimeric iridium(III) precursor complexes with two different ancillary ligands. The regioselectivity of defluorination was evidenced in both cases. The reaction time was identified as a factor strongly impacting the kinetics of the thermally induced reaction.

White and Saturated Blue Phosphorescent OLED based on the Non-Emissive Homoleptic Complex Ir(ppz)3 as single active material

Abstract The well-known homoleptic iridium (III) complex Ir(ppz)3 which is only emissive in solution at low temperature has been investigated as dopant in a p − i stacked OLED architecture. Interestingly, while using this phosphor as a single emitter, awhite OLED was obtained. Emission colour was determined as being concentration and thickness-dependent.

Bis(diphenylamino)naphthalene host materials: careful selection of the substitution pattern for the design of fully solution-processed triple-layered electroluminescent devices

Two new triarylamine-based wide bandgap small molecules differing by the position of their substituents were investigated as hosts for solution-processed organic light-emitting diodes (OLEDs). Blue-green, green and red OLEDs were realized with FIrpic, Ir(ppy)2(acac) and Ir(ppy)2(dbm) as triplet emitters respectively and the three layers constituting the device stacking were successively deposited with orthogonal solvents. Interestingly, one of the two bis(diphenylamino)naphthalene-based compounds, (NAP-1,5-DPA), furnished significantly enhanced EL performances compared to its isomeric counterpart. A maximum luminance of 3905 cd m−2 at 21 V was notably achieved with this material for devices comprising FIrpic as dopant. To get a deeper insight into these major differences in devices, the two host materials were characterized by UV-visible absorption and luminescence spectroscopy, and cyclic voltammetry. Thin films of the two materials were also examined by optical and atomic force microscopy. Thermal properties of the two hosts were also investigated as well as their electronic characteristics by theoretical calculations.