Processable Star-Shaped Molecules with Triphenylamine Core as Hole-Transporting Materials: Experimental and Theoretical Approach

In this study we report on the characterization of five star-shaped π-conjugated molecules by means of UV–vis absorption spectroscopy and electrochemical cyclic voltammetry. These molecules, with triphenylamine (TPA) core bearing one thienothiophene moiety and a different number of thiophene ones, are designed as hole-transporting materials for dye-sensitized solar cell (DSSC) applications. Theoretical calculations employing the B3LYP functional are also carried out in order to understand the structure–property relationships. UV–vis absorption measurements and time-dependent density functional theory (TDDFT) calculations show the presence of intense UV–vis bands for all compounds. These bands are dominated by two degenerate π–π* excitations mostly involving the HOMO → LUMO and HOMO → LUMO+1 transitions. Electrochemical cyclic voltammetry and DFT calculations show the HOMO (LUMO) energy levels increasing (decreasing) with the number of conjugated heterocyclic rings in these molecules. The HOMO energies have been found to vary between −5.38 and −5.13 eV thus showing good positioning with respect to the Fermi level of gold electrode (DSSC applications). The calculated internal reorganization energies (λ_i) suggest for these materials promising hole-transport properties. The analysis of the space extension of the HOMO orbitals as a function of the number of conjugated rings in these molecules gives useful information on their design

π‑Conjugated Dithienophosphole Derivatives as High Performance Photoinitiators for 3D Printing Resins

Photopolymerization and 3D printing applications upon near-UV or visible light are currently limited to both rather low polymerization speed and thin layer by layer productions (below 100 μm) using photoinitiating systems (PIS) mainly inherited from the 1990s. Filling the need for new PIS, two π-conjugated dithienophosphole derivatives (DTPs) are synthesized and proposed as high performance near-UV and visible light photoinitiators/photoredox catalysts for both free radical polymerization (FRP) of (meth)­acrylates and cationic polymerization (CP) of epoxides (e.g., using light-emitting diode (LED) at 405 nm). Astounding polymerization initiating abilities are found, and high final reactive function conversions are obtained (for multifunctional monomers). Their utilization as materials in laser write and 3D printing experiments is especially carried out with for the first time, about 2 mm 3D printed photopolymers in a one-layer approach. A full picture of the included photochemical mechanisms is additionally given. Originally, dithienophosphole derivatives are featured as metal-free photoinitiators/photoredox catalysts

Multicolor Photoinitiators for Radical and Cationic Polymerization: Monofunctional vs Polyfunctional Thiophene Derivatives

Thiophene and polythiophene derivatives have been prepared and used as photoinitiators upon visible light exposure. Their abilities to initiate, when combined with an iodonium salt (and optionally <i>N</i>-vinylcarbazole), a ring-opening cationic photopolymerization of epoxides and radical photopolymerization of acrylates under various different irradiation sources (i.e., very soft halogen lamp irradiation, laser diode at 405, 457, 473, 532, and 635 nm and blue LED bulb at 462 nm) have been investigated. These systems are characterized by a remarkable performance for purple to red light exposure. They are also particularly efficient for the cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure and lead to the formation of an interpenetrated polymer network IPN (30 s for getting tack-free coatings). Their migration stability is excellent in the cured IPNs. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques