The D‐π‐A type phosphonium salts in which electron acceptor (A=‐+PR3) and donor (D=‐NPh2) groups are linked by polarizable π‐conjugated spacers show intense fluorescence that is classically ascribed to excited‐state intramolecular charge transfer (ICT). Unexpectedly, salts with π=‐(C6H4)n‐ and ‐(C10H6C6H4)‐ exhibit an unusual dual emission (F1 and F2 bands) in weakly polar or nonpolar solvents. Time‐resolved fluorescence studies show a successive temporal evolution from the F1 to F2 emission, which can be rationalized by an ICT‐driven counterion migration. Upon optically induced ICT, the counterions move from ‐+PR3 to ‐NPh2 and back in the ground state, thus achieving an ion‐transfer cycle. Increasing the solvent polarity makes the solvent stabilization dominant, and virtually stops the ion migration. Providing that either D or A has ionic character (by static ion‐pair stabilization), the ICT‐induced counterion migration should not be uncommon in weakly polar to nonpolar media, thereby providing a facile avenue for mimicking a photoinduced molecular machine‐like motion.

Rationally designed cationic phospha‐polyaromatic fluorophores were prepared through intramolecular cyclization of the tertiary ortho ‐(acene)phenylene‐phosphines mediated by Cu II triflate. As a result of phosphorus quaternization, heterocyclic phosphonium salts 1 c – 3 c , derived from naphthalene, phenanthrene, and anthracene cores, exhibited very intense blue to green fluorescence ( Φ em =0.38–0.99) and high photostability in aqueous medium. The structure–emission relationship was further investigated by tailoring the electron‐donating functions to the anthracene moiety to give dyes 4 c – 6 c with charge‐transfer character. The latter significantly decreases the emission energy to reach near‐IR region. Thus, the intramolecular phosphacyclization renders an ultra‐wide tuning of fluorescence from 420 nm ( 1 c ) to 780 nm ( 6 c ) in solution, extended to 825 nm for 6 c in the solid state with quantum efficiency of approximately 0.07. The physical behavior of these new dyes was studied spectroscopically, crystallographically, and electrochemically, whereas computational analysis was used to correlate the experimental data with molecular electronic structures. The excellent stability, water solubility, and attractive photophysical characteristics make these phosphonium heterocycles powerful tools in cell imaging.

The series of chelating phosphine ligands, which contain bidentate P 2 (bis[(2-diphenylphosphino)phenyl] ether, DPEphos; 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Xantphos; 1,2-bis(diphenylphosphino)benzene, dppb), tridentate P 3 (bis(2-diphenylphosphinophenyl)phenylphosphine), and tetradentate P 4 (tris(2-diphenylphosphino)phenylphosphine) ligands, was used for the preparation of the corresponding dinuclear [M(μ 2 -SCN) P 2 ] 2 (M = Cu, 1 , 3 , 5 ; M = Ag, 2 , 4 , 6 ) and mononuclear [CuNCS( P 3 /P 4 )] ( 7 , 9 ) and [AgSCN( P 3 /P 4 )] ( 8 , 10 ) complexes. The reactions of P 4 with silver salts in a 1:2 molar ratio produce tetranuclear clusters [Ag 2 (μ 3 -SCN)(t-SCN)( P 4 )] 2 ( 11 ) and [Ag 2 (μ 3 -SCN)( P 4 )] 2 2+ ( 12 ). Complexes 7 – 11 bearing terminally coordinated SCN ligands were efficiently converted into derivatives 13 – 17 with the weakly coordinating – SCN:B(C 6 F 5 ) 3 isothiocyanatoborate ligand. Compounds 1 and 5 – 17 exhibit thermally activated delayed fluorescence (TADF) behavior in the solid state. The excited states of thiocyanate species are dominated by the ligand to ligand SCN → π(phosphine) charge transfer transitions mixed with a variable contribution of MLCT. The boronation of SCN groups changes the nature of both the S 1 and T 1 states to (L + M)LCT d,p(M, P) → π(phosphine). The localization of the excited states on the aromatic systems of the phosphine ligands determines a wide range of luminescence energies achieved for the title complexes (λ em varies from 448 nm for 1 to 630 nm for 10c ). The emission of compounds 10 and 15 , based on the P 4 ligand, strongly depends on the solid-state packing (λ em = 505 and 625 nm for...

The series of cyanide-bridged coordination polymers [(P )CuCN] (1), [(P )Cu{M(CN) }] (M=Cu 3, Ag 4, Au 5) and molecular tetrametallic clusters [{(P )MM'(CN)} ] (MM'=Cu 6, Ag 7, AgCu 8, AuCu 9, AuAg 10) were obtained using the bidentate P and tetradentate P phosphane ligands (P =1,2-bis(diphenylphosphino)benzene; P =tris(2-diphenylphosphinophenyl)phosphane). All title complexes were crystallographically characterized to reveal a zig-zag chain arrangement for 1 and 3-5, whereas 6-10 possess metallocyclic frameworks with different degree of metal-metal bonding. The d -d interactions were evaluated by the quantum theory of atoms in molecules (QTAIM) computational approach. The photophysical properties of 1-10 were investigated in the solid state and supported by theoretical analysis. The emission of compounds 1 and 3-5, dominated by metal-to-ligand charge transfer (MLCT) transitions located within {CuP } motifs, is compatible with thermally activated delayed fluorescence (TADF) behaviour and a small energy gap between the T and S excited states. The luminescence characteristics of 6-10 are strongly dependent on the composition of the metal core; the emission band maxima vary in the range 484-650 nm with quantum efficiency reaching 0.56 (6). The origin of the emission for 6-8 and 10 at room temperature is assigned to delayed fluorescence. AuCu cluster 9, however, exhibits only phosphorescence that corresponds to theoretically predicted large value ΔE(S -T ). DFT simulation highlights a crucial impact of metallophilic bonding on the nature and energy of the observed emission, the effect being greatly enhanced in the excited state.

A potentially tridentate hemilabile ligand, PPh2-C6H4-PPh(O)-C6H4-PPh2 (P(3)O), has been used for the construction of a family of bimetallic complexes [MM'(P(3)O)2](2+) (M = M' = Cu (1), Ag (2), Au (3); M = Au, M' = Cu (4)) and their mononuclear halide congeners M(P(3)O)Hal (M = Cu (5-7), Ag (8-10)). Compounds 1-10 have been characterized in the solid state by single-crystal X-ray diffraction analysis to reveal a variable coordination mode of the phosphine-oxide group of the P(3)O ligand depending on the preferable number of coordination vacancies on the metal center. According to the theoretical studies, the interaction of the hard donor P[double bond, length as m-dash]O moiety with d(10) ions becomes less effective in the order Cu > Ag > Au. 1-10 exhibit room temperature luminescence in the solid state, and the intensity and energy of emission are mostly determined by the nature of metal atoms. The photophysical characteristics of the monometallic species were compared with those of the related compounds M(P(3))Hal (11-16) with the non-oxidized ligand P(3). It was found that in the case of the copper complexes 5-7 the P(3)O hybrid ligand introduces effective non-radiative pathways of the excited state relaxation leading to poor emission, while for the silver luminophores the P[double bond, length as m-dash]O group leads mainly to the modulation of luminescence wavelength.

The coordination chemistry of the tri- and tetradentate chelating phosphines (2-PPh2C6H4)2P­(O)­Ph ( P 3 O ) and (2-PPh2C6H4)3P ( P 4 ) with respect to d10 copper subgroup metal ions has been investigated. Depolymerization of (MC2R) n (M = Cu, Ag) with P 4 affords the series of mono- and trinuclear complexes ( P 4 )­CuC2Ph (1), ( P 4 )­Cu3(C2Ph)3 (2), ( P 4 )­Ag3(C2Ph) (Hal)2 (Hal = Cl (3), Br (4), I (5)). Reactions of the M+ (M = Cu, Ag) ions with (M′C2R) n (M′ = Cu, Ag, Au) acetylides in the presence of P 4 yield the family of dinuclear species [( P 4 )­MM′(C2R)]+ (6–12), which comprise the Cu2/Ag2 (6, 7; R = Ph), AuCu (8–10; R = Ph, C­(OH)­Me2, C­(OH)­Ph2), and AuAg (11, 12; R = Ph, C­(OH)­Ph2) metal cores. A related triphosphine, (2-PPh2C6H4)2PPh ( P 3 ), applied in a similar protocol undergoes partial oxidation and leads to the heterotrimetallic clusters [{( P 3 O )­M}2Au­(C2R)2]+ (M = Cu, R = C­(OH)­Ph2, 13; M = Ag, R = C­(OH)­Ph2, 14; M = Ag, R = Ph, 15), which can be prepared more efficiently starting from the oxidized ligand P 3 O . The structures of the complexes 1–4 and 6–15 were established by single-crystal X-ray crystallography. According to the variable-temperature 1H and 31P­{1H} NMR experiments, compounds 1–12 demonstrate fluxional behavior in solution. The title complexes do not show appreciable luminescence in solution at 298 K, and the photophysical properties of 1–15 were studied in the solid state. The observed phosphorescence (Φem up to 0.46, λem from 440 to 635 nm) is assigned to cluster-centered transitions mixed with some MLCT d → π*­(alkynyl) character.

The high element abundance and d10 electron configuration make ZnII‐based compounds attractive candidates for the development of novel photoactive molecules. Although a large library of purely fluorescent compounds exists, emission involving triplet excited states is a rare phenomenon for zinc complexes. We have investigated the photophysical and ‐chemical properties of a series of dimeric and monomeric ZnII halide complexes bearing a cyclic (alkyl)(amino)carbene (cAAC) as chromophore unit. Specifically, [(cAAC)XZn(μ‐X)2ZnX(cAAC)] (X=Cl (1), Br (2), I (3)) and [ZnX2(cAAC)(NCMe)] (X=Br (4), I (5)) were isolated and fully characterized, showing intense visible light photoluminescence under UV irradiation at 297 K and fast photo‐induced transformation. At 77 K, the compounds exhibit improved stability allowing to record ultra‐long lifetimes in the millisecond regime. DFT/MRCI calculations confirm that the emission stems from 3XCT/LEcAAC states and indicate the phototransformation to be related to asymmetric distortion of the complexes by cAAC ligand rotation. This study enhances our understanding of the excited state properties for future development and application of new classes of ZnII phosphorescent complexes.

Preparation and photoluminescence properties of graphene quantum dots by decomposition of graphene-encapsulated metal nanoparticles derived from Kraft lignin and transition metal salts Temerov, Filipp Elsevier BV Tieteelliset aikakauslehtiartikkelit