Achieving yellow emission by varying the donor/acceptor units in rod-shaped fluorenyl-alkynyl based π-conjugated oligomers and their binuclear gold(i) alkynyl complexes

Highly emissive supramolecular gold(I)-BTD materials

Herein we report the synthesis of three light emitting rod-shaped gold(I) complexes by combining ethynyl-functionalized 2,1,3-benzothiadiazole (BTD), with different N-heterocyclic (imidazole, benzimidazole and phenantroimidazole) carbene gold(I) complexes. As could be determined by single crystal structure determination, the size of the N-heterocyclic carbene affects the relative disposition of the two ligands in the linear gold complexes (nearly perpendicular in the benzimidazole vs. planar in the phenantroimidazole derivative) which translates to different types of interactions between neighbouring units. In fact, the planar conformation in the more π-extended phenantroimidazole carbene allows Au(I) atoms to get sufficiently closer favouring aurophilic interactions. This compound is obtained as two different colour emitting solids which is ascribed to changes in packing modes probably leading to differences in the strength of aurophilic interactions. Interestingly, while the emission in the solid state is almost quenched, the incorporation of the compounds in polymer matrixes enhances the emissive properties of the compounds reaching near unity quantum yields.

Unexpectedly Long Lifetime of the Excited State of Benzothiadiazole Derivative and Its Adducts with Lewis Acids

We report a study of photoluminescent properties of 4-bromo-7-(3-pyridylamino)-2,1,3-benzothiadiazole (Py-btd) and its novel Lewis adducts: (PyH-btd)₂(ZnCl₄) and [Cu₂Cl₂(Py-btd)₂{PPO}₂]·2C₇H₈ (PPO = tetraphenyldiphosphine monoxide), whose crystal structure was determined by X-ray diffraction analysis. Py-btd exhibits a lifetime of 9 microseconds indicating its phosphorescent nature, which is rare for purely organic compounds. This phenomenon arises from the heavy atom effect: the presence of a bromine atom in Py-btd promotes mixing of the singlet and triplet states to allow efficient singlet-to-triplet intersystem crossing. The Lewis adducts also feature a microsecond lifetime while emitting in a higher energy range than free Py-btd, which opens up the possibility to color-tune luminescence of benzothiadiazole derivatives.

Gold(i)-doped films: new routes for efficient room temperature phosphorescent materials

The synthesis of four novel gold(i)-phosphane complexes coordinated to 9-phenanthrene chromophore has been carried out through the reaction of 9-phenanthreneboronic acid and the corresponding AuClPR₃ (PR₃ = PPh₃ for triphenylphosphane (1a); 1,4-bis(diphenylphosphanyl)butane or dppb (2b); bis(diphenylphosphanyl)acetylene or dppa (2c); (AuCl)₂(diphos) (diphos = bis(diphenylphosphanyl)methane or dppm (3)) sources. The X-ray crystal structures of compounds 1a and 2b show the existence of MOF-like intermolecular assemblies that contain empty inner cavities in the absence of aurophilic contacts. In contrast, the formation of a tetranuclear complex with intramolecular aurophilic interactions was evidenced for 3. Photophysical characterization indicates dual emission in all gold(i) complexes when oxygen is removed from the sample, while only fluorescence emission is recorded for the uncoordinated ligand. The introduction of the compounds within PMMA and Zeonex was assayed, and luminescent films containing gold(i) complexes where phosphorescence is the sole pathway for emission are obtained, instead of the dual emission (with significant fluorescence contribution) recorded in solution.

Mild and Efficient Synthesis of Diverse Organo-AuI -L Complexes in Green Solvents

An exceptionally mild and efficient method was developed for the preparation of (hetero)aryl-Au^I -L complexes using ethanol or water as the reaction medium at room temperature and Ar-B(triol)K boronates as the transmetalation partner. The reaction does not need an exogeneous base or other additives, and quantitative yields can be achieved through a simple filtration as the only required purification method, which obviates considerable waste associated with alternative workup methods. A broad reaction scope was demonstrated with respect to both the L and (hetero)aryl ligands on product Au complexes. Despite the polar reaction medium, large polycyclic aromatic hydrocarbon units can be incorporated on the Au complexes in very good to excellent yields. The approach was demonstrated for the chemoselective manipulation of orthogonally protected aryl boronates to afford a new class of N-heterocyclic carbene-Au-aryl complexes. A mechanistic rationale was proposed.

Controlling the supramolecular polymerization of dinuclear isocyanide gold(i) arylethynylene complexes through tuning the central π-conjugated moiety

Tuning the middle chromophores of dinuclear gold(i) arylethynyl complexes has been demonstrated to exhibit a pronounced effect on the photophysical properties, self-assembly mechanisms and morphologies.

Dinuclear gold(i) complexes: from bonding to applications

The last two decades have seen a veritable explosion in the use of gold(i) complexes bearing N-heterocyclic carbene (NHC) and phosphine (PR₃) ligands.

Diruthenium(ii)-capped oligothienylethynyl bridged highly soluble organometallic wires exhibiting long-range electronic coupling

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Near-unity thermally activated delayed fluorescence efficiency in three- and four-coordinate Au(i) complexes with diphosphine ligands

The synthesis and photoluminescence properties of three-coordinate Au(i) complexes with rigid diphosphine ligands LMe {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, LEt {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and LiPr {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene} are investigated. The LMe and LEt ligands afford two types of complexes: dinuclear complexes [μ-LMe(AuCl)2] (1d) and [μ-LEt(AuCl)2] (2d) with an Au(i)-Au(i) bond and mononuclear three-coordinate Au(i) complexes LMeAuCl (1) and LEtAuCl (2). On the other hand, the bulkiest ligand, LiPr, affords three-coordinate Au(i) complexes, LiPrAuCl (3) and LiPrAuI (4), but no dinuclear complexes. X-ray analysis suggests that both 3 and 4 possess a highly distorted trigonal planar geometry. Moreover, luminescence data reveal that at room temperature, 3 and 4 exhibit yellow-green thermally activated delayed fluorescence in the crystalline state with maximum emission wavelengths at 558 and 549 nm, respectively. The emission yields are close to unity. Quantum chemical calculations suggest that the emission of 4 originates from the (σ + X) → π* excited state that possesses strong intraligand charge-transfer character. The luminescent properties of four-coordinate Au(i) complex (5) possessing a tetrahedral geometry are discussed on the basis of the emission spectra and decay times measured in a temperature range of 309-77 K.