No abstract

Cost-efficient thin-film devices that emit in the nearinfrared (NIR) range promise a wide range of important applications. Here, the synthesis and NIR application of a series of copolymers comprising poly [indacenodithieno[3,2-b]thiophene-2,8-diyl] (PIDTT) as the host and different donor−acceptor−donor (DAD) segments as the guest are reported. We find that a key design criterion for efficient solid-state host-to-guest energy transfer is that the DAD conformation is compatible with the conformation of the host. Such host−guest copolymers are evaluated as the emitter in light-emitting electrochemical cells (LECs) and organic light-emitting diodes, and the best performance is invariably attained from the LEC devices because of the observed balanced electrochemical doping that alleviates issues with a noncentered emission zone. An LEC device comprising a host−guest copolymer with 4,4bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene as the donor and benzo[c][1,2,5]thiadiazole as the acceptor delivers an impressive near-infrared (NIR) performance in the form of a high radiance of 1458 μW/cm 2 at a peak wavelength of 725 nm when driven by a current density of 500 mA/cm 2 , a second-fast turn-on, and a good stress stability as manifested in a constant radiance output during 3 days of uninterrupted operation. The high-molecular-weight copolymer features excellent processability, and the potential for low-cost and scalable NIR applications is verified through a spray-coating fabrication of a >40 cm 2 large-area device, which emits intense and uniform NIR light at a low drive voltage of 4.5 V.

Transient absorption spectroelectrochemistry reveals that the singly reduced bridging ligand in a prototype molecular catalyst light driven proton reduction does not allow for electron transfer to the catalytic center – breaking the catalyst's back.

Stable charge‐separated states are key features for using light in various types of solar cells and a broad range of photocatalytic applications. So far, molecular systems often suffer from increased charge recombination after initial excitation. Herein, the scope of molecular model systems for intramolecular electron transfer and charge separation by applying copper‐catalyzed click chemistry to covalently functionalize tris‐heteroleptic ruthenium(II) complexes to yield donor–photosensitizer–acceptor triads with 1,4‐dihydro‐N‐benzyl‐nicotinamide (BNAH) as donor and N‐methyl‐4,4´‐bipyridinium (MQ+) as acceptor is studied. Two triads with electron‐withdrawing or electron‐donating ancillary 2,2´‐bipyridyl ligands are synthesized and their light‐induced intramolecular electron transfer and long‐lived charge‐separated states (τ = 0.8 ms and τ = 1.5 ms) are characterized using steady‐state and time‐resolved spectroscopy and electrochemistry. Additionally, it is found that the charge‐separated state resides on different parts of the molecule within these two triads, allowing for selective directionality of charge transfer within a molecule.

Light-driven hydrogen evolution is one key process in the development of sustainable energy schemes. Here we report the covalent embedding of molecular ruthenium photosensitizers within block copolymer micelles, leading to...

Based on quantum chemical calculations, we predict strong solvatochromism in a light-driven molecular photocatalyst for hydrogen generation, i.e., we show that the electronic and optical properties of the photocatalyst strongly depend on the solvent it is dissolved in. Our calculations in particular indicate a solvent dependent relocation of the highest occupied molecular orbital (HOMO). Ground-state density functional theory and linear response time dependent density functional theory calculations are applied in order to investigate the influence of implicit solvents on the structural, electronic and optical properties of a molecular photocatalyst. Only at high dielectric constants of the solvent, the HOMO is located at the metal center of the photosensitizer, whereas at low dielectric constants the HOMO is centered at the metal atom of the catalytically active complex. We elucidate the electronic origins of this strong solvatochromic effect and sketch the consequences of these insights for the use of photocatalysts in different environments.

Six different monoarylated N‐aryl‐1H‐imidazo[4,5‐f][1,10]phenanthroline (Rip) ligands and their corresponding ruthenium complexes [(tbbpy)2Ru(Rip)]2+ Ru(Rip) have been synthesized bearing different aryl substituents on the imidazole unit including electron donating and accepting groups. N,N’‐disubstitution on the imidazole unit yielded five new 1‐aryl‐3‐benzyl‐1H‐imidazo[4,5‐f][1,10]phenanthrolinium bromide (RR'ip)+ ligands and the corresponding ruthenium complexes [(tbbpy)2Ru(RR'ip)]3+ Ru(RR'ip). All complexes were characterized in terms of their structural, photophysical, photochemical and electrochemical properties. The photophysical data revealed a high luminescence quantum yield (21.6–22.8 %) for monoarylated Ru(Rip) complexes compared to [Ru(bpy)3]2+ (9.5 %) under inert conditions. Generating the imidazolium unit, yielding Ru(RR'ip)‐complexes lead to notable loss of quantum yields. Furthermore, we observed an enhanced photostability of Ru(RR'ip) complexes in the case of ortho substituted aryl groups.