Natural aldehyde extraction and direct preparation of new blue light-emitting imidazo[1,5-a]pyridine fluorophores

<p>This work describes the extraction of natural aldehydes and the use of extracts to synthesise new fluorescent imidazo[1,5-a]pyridine derivatives. The characterisation of the extracted aldehydes by different techniques and the optical study of the fluorescent products allow the design of new compounds suitable for pharmaceutical, down-shifting, microscopy and electronic applications. The fluorophores are generated by an easy one-pot cyclisation reaction in mild conditions without catalyst and with only water as by-product.</p

Novel Ligand and Device Designs for Stable Light-Emitting Electrochemical Cells Based on Heteroleptic Copper(I) Complexes

This work reports on the positive impact of (i) attaching methoxy groups at the ortho position of the bipyridine ligand (6,6′-dimethoxy-2,2′-bipyridine) in heteroleptic copper­(I) complexes belonging to the [Cu­(bpy)­(POP)]⁺ family, and (ii) a new device design comprising a multilayered architecture to decouple hole/electron injection and transport processes on the performance of light-emitting electrochemical cells (LECs). In short, the substituted complex showed enhanced thermal- and photostability, photoluminescence, and ionic conductivity features in thin films compared to those of the archetypal complex without substitution. These beneficial features led to LECs outperforming reference devices in terms of luminance, stability, and efficacy. Furthermore, a new device design resulted in a 10-fold enhancement of the stability without negatively affecting the other figures of merit. Here, hole/electron injection and transport processes are performed at two different layers, while electron injection and electron–hole recombination occur at the copper­(I) complex layer. As such, this work provides further insights into a smart design of N^N ligands for copper­(I) complexes, opening the path to a simple device architecture toward an enhanced electroluminescence response

Photophysics of Singlet and Triplet Intraligand Excited States in [ReCl(CO)₃(1-(2-pyridyl)-imidazo[1,5-α]pyridine)] Complexes

Excited-state characters and dynamics of [ReCl­(CO)₃(3-R-1-(2-pyridyl)-imidazo­[1,5-α]­pyridine)] complexes (abbreviated <b>ReGV-R</b>, R = CH₃, Ph, PhBu^<i>t</i>, PhCF₃, PhNO₂, PhNMe₂) were investigated by pico- and nanosecond time-resolved infrared spectroscopy (TRIR) and excited-state DFT and TD-DFT calculations. Near UV excitation populates the lowest singlet state S₁ that undergoes picosecond intersystem crossing (ISC) to the lowest triplet T₁. Both states are initially formed hot and relax with ∼20 ps lifetime. TRIR together with quantum chemical calculations reveal that S₁ is predominantly a ππ* state localized at the 1-(2-pyridyl)-imidazo­[1,5-α]­pyridine (= impy) ligand core, with impy → PhNO₂ and PhNMe₂ → impy intraligand charge-transfer contributions in the case of <b>ReGV-PhNO</b>_<b>2</b> and <b>ReGV-PhNMe</b>_<b>2</b>, respectively. T₁ is predominantly ππ*­(impy) in all cases. It follows that excited singlet and corresponding triplet states have to some extent different characters and structures even if originating nominally from the same preponderant one-electron excitations. ISC occurs with a solvent-independent (CH₂Cl₂, MeCN) 20–30 ps lifetime, except for <b>ReGV-PhNMe</b>_<b>2</b> (10 ps in CH₂Cl₂, 100 ps in MeCN). ISC is 200–300 times slower than in analogous complexes with low-lying MLCT states. This difference is interpreted in terms of spin–orbit interaction and characters of orbitals involved in one-electron excitations that give rise to S₁ and T₁ states. <b>ReGV-R</b> present a unique case of octahedral heavy-metal complexes where the S₁ lifetime is long enough to allow for separate spectroscopic characterization of singlet and triplet excited states. This study provides an insight into dynamics and intersystem crossing pathways of low-lying singlet and triplet excited states localized at bidentate ligands bound directly to a heavy metal atom. Rather long ¹IL lifetimes indicate the possibility of photonic applications of singlet excited states