Phospha-cyanines in Their Ideal Polymethine State: Synthesis and Structure-Property Relationships

We report the synthesis and full characterization of a family of phosphorus-containing polymethine cyanines (phospha-cyanines). The compounds are easily prepared in two steps, starting from readily available phosphanes. The impact of the P-substituents and the counterions on the structural and optical properties is investigated through a joint experimental/theoretical approach. Based on the study of the single-crystal X-ray diffraction structures, all phospha-cyanines present a bond length alternation close to zero, independently of the substituents and counterions, which indicates an ideal polymethine state. All these compounds display the typical cyanine-like UV-vis absorption with an intense and sharp transition with a vibronic shoulder despite possessing a reverse electronic configuration compared to "classical" cyanines. Time-dependent density-functional theory calculations allowed us to fully rationalize the optical properties (absorption/emission wavelengths, luminescence quantum yields). Interestingly, due to the tetrahedral shape of the P atom, the optical properties are independent of the counterion, which is in marked contrast with N-analogues, which enables predictive engineering of the phospha-cyanines regardless of the medium in which they are used.

Tetrazo[1,2-b]indazoles: Straightforward Access to Nitrogen-Rich Polyaromatics from s-Tetrazines

The straightforward access to a new class of aza-polyaromatics is reported. Starting from readily available fluorinated s-tetrazine, a cyclization process with azide leads to the formation of an unprecedented tetrazo[1,2-b]indazole or a bis-tetrazo[1,2-b]indazole (cis and trans conformers). Based on the new nitrogen core, further N-directed palladium-catalyzed ortho-C-H bond functionalization allows the introduction of halides or acetates. The physicochemical properties of these compounds were studied by a joint experimental/theoretical approach. The tetrazo[1,2-b]indazoles display solid-state π-stacking, low reduction potential, absorption in the visible range up to the near-infrared, and intense fluorescence, depending on the molecular structure.

Novel Metallo-Supramolecular Polymers with 1-Thioxophosphole Main-Chain Units and Remarkable Photoinduced Changes in Their Resonance Raman Spectra

New low-bandgap unimers, with the central thiophene-(1-thioxophosphole)-thiophene (TPT) ring sequence and 2,2':6',2″-terpyridin-4'-yl (tpy) end groups connected to the central unit via conjugated linkers of different size, are prepared and assembled with Zn(II) and Fe(II) ions to metallo-supramolecular polymers (MSPs) that are studied regarding their properties. The most interesting feature of Zn-MSPs is the luminescence extended deep into the NIR region. Fe-MSPs not only show the metal-to-ligand charge transfer (MLCT) manifested by the MLCT band (an expected feature) but also an as-yet-undescribed remarkable phenomenon: specific damping of the bands of the TPT sequence in the resonance Raman spectra taken from solid Fe-MSPs using the excitation to the MLCT band (532 nm). The damping is highly reversible at the low laser power of 0.1 mW but gradually becomes irreversible as the power reaches ca. 5 mW. The revealed phenomenon is not shown by the same Fe-MSPs in solutions, nor by Fe-MSPs containing no phosphole units. A hypothesis is proposed that explains this phenomenon and its dependence on the irradiation intensity as a result of the interplay of three factors: (i) enhancement of the MLCT process by excitation radiation, (ii) the electron-acceptor character of the 1-thioxophosphole ring, and (iii) morphological changes of the lattice and their dependence on the population of new structures in the lattice.

Tuning the Charge Transfer in λ5-Phosphinines with Amino Substituents

We report the substitution of λ⁵-phosphinines (2,6-dicarbonitrile diphenyl-1-λ⁵-phosphinine) with an amino group. The impact of these modifications on both the optical and redox properties is investigated using a joint experimental/theoretical approach. In particular, we show that the choice of the donor diphenylamino group dramatically impacts the nature of the charge transfer. The use of di(methoxyphenyl)amine redshifts the optical properties and allows thermally activated delayed fluorescence in the solid state. Finally, we demonstrated that λ⁵-phosphinines with an amino group can be used as active emitters in an electroluminescent device.

Straightforward Access to Multifunctional π‐Conjugated P‐Heterocycles Featuring an Internal Ylidic Bond**

We report the straightforward one‐pot synthesis of novel 5‐ or 6‐membered P‐heterocycles featuring an internal ylidic bond: P‐containing acenaphthylenes and phenanthrenes. The stability of the compounds tolerates post‐functionalization through direct arylation to introduce electron‐rich/poor substituents and the synthetic strategy is also compatible with the preparation of more elaborate polyaromatic scaffolds such as acenes and helicenes. Using a joint experimental (X‐ray analysis, optical and redox properties) and theoretical approach, we perform a full structure–property relationships study on these new platforms. In particular, we show that molecular engineering allows not only tuning their absorption/emission across the entire visible range but also endowing them with chiroptical or non‐linear optical properties, making them valuable dyes for a large panel of photonic or opto‐electronic applications.

Organophosphorus emitters for OLEDs

In this paper, we present the development of OLEDs using organophosphorus derivatives as emitters. In this study, we were able to show that the structural variations carried out on phospholes, phosphinines and phosphepines (functionalization of the phosphorus atom, nature of the substituents) make it possible to modulate the emission wavelengths and, thus, the emission colour of the diodes. Using this concept, we were able to develop TADF and chiral organophosphorus emitters and hybrids emitting at different wavelengths which can be used for the development of OLEDs. The diode structures used are simple and provide high external quantum yields.

Si-containing polycyclic aromatic hydrocarbons: synthesis and opto-electronic properties

We report a straightforward synthesis of Si-containing Polycyclic Aromatic Hydrocarbons (PAHs). The impact of π-extension and exocyclic modifications on both the optical and redox properties is investigated using a joint experimental/theoretical approach. By taking advantage of the solid-state luminescence of these derivatives, electroluminescent devices are prepared. Such preliminary opto-electronic results highlight that these heteroatom-containing PAHs are promising building blocks for organic electronics.

Taking Advantage of Ortho- and Peri-Substitution to Design Nine-Membered P,O,Si-heterocycles*

A family of cyclic phosphine-disiloxane featuring peri-substituted naphthyl(Nap)/acenaphthyl(Ace) scaffolds has been prepared and fully characterized including X-ray structure, which enables a detailed structural analysis. This straightforward synthesis takes advantage of both ortho- and peri-substitution of Nap/Ace-substituted phosphine oxides. The synthetic method allows diversifying the polycyclic aromatic platform (Nap and Ace) as well as the Si substituents (Me and Ph). Despite a strong steric congestion, the P-atom remains reactive toward oxidation or coordination. In particular, Au(I) complex could be prepared. All the compounds display absorption/luminescence in the UV-Vis range. Surprisingly, the P-trivalent derivatives display unexpected luminescence in the green in solid-state.

Stereospecific synthesis of chiral P-containing polyaromatics based on 7-membered P-rings

We present the stereospecific synthesis of helicenoid-based phosphepines (7-membered P-rings) as well as chiral P-containing polycyclic aromatic hydrocarbons. In these systems, an axial to central chirality transfer takes place from the BINAP moiety to the P-atom. The impact of the molecular design on the structure, the (chir)optical (including circularly polarized luminescence) and redox properties are investigated.

The influence of the formal replacement of thiophenes by stannoles in terthiophene and sexithiophene on the optoelectronic properties and electrochemical behavior

Polystannoles with thienyl co-monomers are in many ways similar to polythiophenes, but they display much reduced band gaps. However, their polymerization processes are not well researched. Thiophene can be oxidatively electropolymerized, but as stannoles are organometallic, the fundamental question arises whether their inclusion in a conjugated backbone can protect them sufficiently to be able to perform an oxidative electropolymerization. As well-defined oligothiophenes can be used as models to understand the optical and electronic properties of polythiophenes, we transposed this concept on stannole containing polymers; therefore we synthesized a monomeric 1 and dimeric thiophene-flanked stannole 2 and investigated their optoelectronic properties comparatively including polystannoles and the corresponding oligothiophenes in our analysis. With respect to monomer 1, a significantly redshifted absorption (λmax = 510 nm, Δ = 93 nm) and a small optical band gap (Eg,opt(2) = 2.13 eV), close to the bandgap of polymeric stannoles, was observed. In comparison to oligothiophenes, these thienyl-flanked stannoles exhibited a redshift in absorption and emission as well as a lower oxidation potential. Despite these differences, they showed an oligothiophene-like electrochemical behavior. Stannole 1 and the dimer 2 were subjected to an electropolymerization process. This process was investigated in detail by spectroelectrochemical methods which showed that radical cation species were formed in situ but readily decomposed. Nevertheless, under the milder multiscan cyclovoltammetric conditions, electropolymerization occurred as shown by cyclovoltammetry.

Stereochemical Control of Tricoordinate Copper(I) Complexes Based on N-(9-Alkyl-9-fluorenyl)-Substituted Heterocyclic Carbenes

A series of tricoordinate copper(I) complexes of general formula [Cu(Et F-NHC)(2,2′-dipyridylamine)][BF4], in which Et F-NHC represents an imidazol-2-ylidene ligand bearing a 9-ethyl-9-fluorenyl N-substituent have been synthesised stepwise from appropriate N-arylimidazoles. All complexes are remarkably air-stable, both in solution and in the solid state. X-ray diffraction studies revealed that in three of the complexes the fluorenylidene plane and the dipyridylamine (dpa) unit undergo intramolecular π–π stacking. The resulting bending of the fluorenilydene plane towards the metal atom is likely to contribute to maintain the trigonal planar geometry of the [Cu–C,N,N] unit upon binding of exogenous substrates, thereby considerably increasing complex stability.

Topologically diverse polycyclic aromatic hydrocarbons from pericyclic reactions with polyaromatic phospholes

Topologically divers PAHs with planar, twisted and negatively curved topologies were obtained from polycyclic phospholes using pericyclic reactions.

Synthesis, Electronic Properties and OLED Devices of Chromophores Based on λ5 -Phosphinines

A new series of 2,4,6-triaryl-λ5 -phosphinines have been synthesized that contain different substituents both on the carbon backbone and the phosphorus atom of the six-membered heterocycle. Their optical and redox properties were studied in detail, supported by in-depth theoretical calculations. The modularity of the synthetic strategy allowed the establishment of structure-property relationships for this class of compounds and an OLED based on a blue phosphinine emitter could be developed for the first time.

Naphthyl-Fused Phosphepines: Luminescent Contorted Polycyclic P-Heterocycles

This article presents the synthesis of a new family of naphthyl-fused phosphepines through Ni-mediated C-C coupling. Interestingly, the chlorophosphine oxide intermediate shows strong resistance toward oxidation/hydrolysis owing to a combination of steric hindrance and pnictogen interactions. However, it can undergo substitution reactions under specific conditions. The optical/redox properties and the electronic structure of these new π-systems were studied experimentally (UV/Vis absorption, emission, cyclic voltammetry) and computationally (TD-DFT calculations, NICS investigation). Taking advantage of the luminescence of these derivatives, a blue-emitting OLED has been prepared, highlighting that these novel π-conjugated P-heterocycles appear to be promising building blocks for solid-state lighting applications.

Phosphahelicenes: From Chiroptical and Photophysical Properties to OLED Applications

Herein, the experimental physicochemical and chiroptical properties of a series of phosphahelicenes are reported, focusing on their UV/Vis absorption, luminescence, electronic circular dichroism, optical rotations, and circularly polarized luminescence. Furthermore, detailed analysis of absorption and ECD spectra performed with the help of quantum-chemical calculations allowed us to highlight general features of these helicenic phosphines. Finally, due to well-suited electrochemical properties and thermal stability, the systems were successfully used as emitters in organic light-emitting diodes.

π-Extended Phosphepines: Redox and Optically Active P-Heterocycles with Nonplanar Framework

In this letter, we present the synthesis of a new family of π-extended dithieno[ b, f]phosphepines. The Pd-catalyzed direct arylation allows the introduction of various substituents, which tune the absorption/emission in the visible range as well as the redox properties. All those modifications were rationalized through DFT calculations. The physical properties of ambipolar phosphepine with diphenylamino substituents inspired us to use it as a semiconductor in p-type organic field-effect transistors (OFETs).

Synthesis, Optical, and Redox Properties of Regioisomeric Benzoheterocycles-Fused Pyrene

A new synthetic route toward the synthesis of benzo[b]phospholes- and benzo[b]siloles-fused pyrenes using a transition metal-catalyzed C-H bond activation is described. The compounds were fully characterized including X-ray diffraction. A combined experimental and theoretical study shows that both the heteroatom and the substitution pattern impact the optical and redox properties.

Conjugated oligomers with alternating heterocycles from a single monomer: synthesis and demonstration of electroluminescence

A synthetic strategy for push–pull oligomers is based on a nucleophile and electrophile selective synthesis of the corresponding monomers.

Tuning the Optoelectronic Properties of Stannoles by the Judicious Choice of the Organic Substituents

Stannoles are organometallic rings in which the heteroatom is involved in a form of conjugation that is called σ*-π* conjugation. Only very little is known about how the substituents on the Sn atom or substituents on the stannole ring determine the optoelectronic properties of these heterocycles. In this work, this question has been studied experimentally and theoretically. Calculations of optimized equilibrium geometries, energy gaps between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), and of the absorption spectra of a wide range of compounds were performed. The computational data showed that the substituents on the Sn atom influence the optoelectronic properties to a lower extent than the substituents in the 2 and 5 positions of the ring. These substituents in the 2 and 5 positions of the stannole ring can also have a strong influence on the overall planarity of the structure, in which mesomeric effects can play a substantial role only if the structure is planar. Thus, only structures with a planar backbone are of interest in the context of tuning the optoelectronic properties. These were selected for the experimental studies. On the basis of this information, a series of six novel stannoles was synthesized by the formation of a zirconium intermediate and subsequent transmetalation to obtain the tin compound. The calculated electronic HOMO-LUMO energy gaps varied between 2.94 and 2.68 eV. The measured absorption maxima were located between 415 and 448 nm compared to theoretically calculated values ranging from 447 nm (2.77 eV) to 482 nm (2.57 eV). In addition to these optical measurements, cyclic voltammetry data could be obtained, which show two reversible oxidation processes for three of the six stannoles. With this study, it could be demonstrated how the judicious choice of the substituents can lead to large and predictable bathochromic shifts in the absorption spectra.

Reaction of carbonyl trinuclear clusters with 2,5-bis(2-thienyl)-1-phenyl-phosphole as a ligand: a new pathway to ruthenacyclopentadiene and cyclopentadienone ruthenium complexes

A novel pathway for the formation of ruthenacyclopentadiene and cyclopentadienone ruthenium complexes is described.

Supramolecular assembly of a phosphole-based moiety into nanostructures dictated by alkynylplatinum(ii) terpyridine complexes through non-covalent Pt···Pt and π-π stacking interactions: synthesis, characterization, photophysics and self-assembly behaviors

A new class of platinum(ii) terpyridine complexes with a phosphole-derived bridging alkynyl ligand have been prepared. The X-ray crystal structure of complex 2 has been determined, and reveals a polymeric zig-zag chain structure with the existence of π-π stacking interactions. The photophysical properties have also been studied, with 3MLCT/3LLCT phosphorescence exhibited in degassed CH2Cl2; the energy of which is varied by the π-conjugation of the terpyridine ligands. The solvent-induced assembly of complex 1 has been studied. The incorporation of hydrophobic hydrocarbon chains has been shown to play an important role in assisting the formation of self-assembled nanostructures via Pt···Pt, π-π stacking and hydrophobic-hydrophobic interactions. It has been established that an isodesmic growth mechanism operates in polar media to give nanospheres, while fibrous networks originate from the self-assembly of the complexes in non-polar media, predominantly driven by π-π stacking interactions.

Strategies toward phosphorus-containing PAHs and the effect of P-substitution on the electronic properties

In this paper, we report on the different synthetic strategies which led to the preparation of a whole family of polyaromatic hydrocarbons containing a P-atom at the edge. In particular, we show from both experimental and theoretical perspective how the Scholl method has to be adapted to the specificity of organophosphorus derivatives. The P-modified PAHs possess the classical phosphane reactivity that allows fine-tuning of their electronic properties as evidenced by spectro-electrochemistry and theoretical calculations. In particular, the effect of P-substitution on the aromaticity of the different cycles of the PAH was studied.

Calix[4]arene-fused phospholes

A calix[4]arene-based biarylphosphine has been synthesised and catalytically converted into two diastereomeric, calixarene-fused phospholes.

π-Conjugated phospholes and their incorporation into devices: components with a great deal of potential

This review serves as a brief introduction to phospholes and discusses their unique favorable properties for application in organic electronic materials. Over the past several years, π-conjugated phospholes have been slowly making their way into devices. We report here the mode of synthesis of these π-conjugated phospholes as well as discuss the performances of the devices.

Synthesis and electronic properties of polycyclic aromatic hydrocarbons doped with phosphorus and sulfur

Synthesis and physical properties of polyaromatic hydrocarbons containing phosphole and thiophene rings at the edge.

Molecular-structure control of electron transfer dynamics of push–pull porphyrins as sensitizers for NiO based dye sensitized solar cells

Zn(ii)-porphyrin dyes for NiO dye-sensitized solar cells showed surprisingly rapid charge recombination, in spite of their push–pull character. Appending a secondary acceptor prolonged charge separation and led to improved photovoltaic performance.

1,2-dihydrophosphete: a platform for the molecular engineering of electroluminescent phosphorus materials for light-emitting devices

The discovery and molecular engineering of novel electroluminescent materials is still a challenge in optoelectronics. In this work, the development of new π-conjugated oligomers incorporating a dihydrophosphete skeleton is reported. Variation of the substitution pattern of 1,2-dihydrophosphete derivatives and chemical modification of their P atoms afford thermally stable derivatives, which are suitable emitters to construct organic light-emitting diodes (OLEDs). The optical and electrochemical properties of these new P-based oligomers have been investigated in detail and are supported by DFT calculations. The OLED devices exhibit good performance and current-independent CIE coordinates.

Phosphorus centers of different hybridization in phosphaalkene-substituted phospholes

Phosphole-substituted phosphaalkenes (PPAs) of the general formula Mes*P=C(CH(3))-(C(4)H(2)P(Ph))-R 5 a-c (Mes*=2,4,6-tBu(3)Ph; R=2-pyridyl (a), 2-thienyl (b), phenyl (c)) have been prepared from octa-1,7-diyne-substituted phosphaalkenes by utilizing the Fagan-Nugent route. The presence of two differently hybridized phosphorus centers (σ(2) ,λ(3) and σ(3) ,λ(3)) in 5 offers the possibility to selectively tune the HOMO-LUMO gap of the compounds by utilizing the different reactivity of the two phosphorus heteroatoms. Oxidation of 5 a-c by sulfur proceeds exclusively at the σ(3) ,λ(3) -phosphorus atom, thus giving rise to the corresponding thioxophospholes 6 a-c. Similarly, 5 a is selectively coordinated by AuCl at the σ(3),λ(3) -phosphorus atom. Subsequent second AuCl coordination at the σ(2),λ(3) -phosphorus heteroatom results in a dimetallic species that is characterized by a gold-gold interaction that provokes a change in π conjugation. Spectroscopic, electrochemical, and theoretical investigations show that the phosphaalkene and the phosphole both have a sizable impact on the electronic properties of the compounds. The presence of the phosphaalkene unit induces a decrease of the HOMO-LUMO gap relative to reference phosphole-containing π systems that lack a P=C substituent.