Derivatives of 2-(2′-hydroxy-5′-dimethylaminobenzyl)-4,6-dimethylamino-1,3,5-triazine were synthesized by an original multistep protocol that afforded, after quaternization of the N,N-dimethylaminobenzyl moiety, water-soluble fluorescent dyes. These fluorophores exhibited excited-state intramolecular proton transfer and large Stokes shifts (Δ_SS > 10000 cm^–1). The phenol residue was masked by an enzyme-labile protecting group based on self-immolative para-hydroxybenzyl alcohol. Lipases were used to unveil the fluorescence under physiological conditions (phosphate-buffered saline, pH 7.2) without aggregation or precipitation of the fluorescent dyes.

Differently substituted anils (Schiff bases) and their boranil counterparts lacking the proton-transfer functionality have been studied using stationary and femtosecond time-resolved absorption, fluorescence, and IR techniques, combined with quantum mechanical modelling. Dual fluorescence observed in anils was attributed to excited state intramolecular proton transfer. The rate of this process varies upon changing solvent polarity. In the nitro-substituted anil, proton translocation is accompanied by intramolecular electron transfer coupled with twisting of the nitrophenyl group. The same type of structure is responsible for the emission of the corresponding boranil. A general model was proposed to explain different photophysical responses to different substitution patterns in anils and boranils. It is based on the analysis of changes in the lengths of CN and CC bonds linking the phenyl moieties. The model allows predicting the contributions of different channels that involve torsional dynamics to excited state depopulation.

This paper describes the synthesis of π-conjugated fluorophores based either on an anil or a benzoxazole scaffold incorporating a rigid 2-(6′-hydroxy-5′-benzofuryl) fragment. Their subsequent coordination to a BF₂ motif led to highly luminescent B^III complexes called boranils or HBBO borate complexes, respectively. All the new compounds were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. The study of their optical properties in solution revealed two distinct photophysical behaviors depending on the substitution. Complexes bearing a strong electron-donating p-nBu₂NC₆H₄ group displayed a marked internal charge transfer (ICT) leading to a pronounced solvatochromism with λ_em ranging from 507 to 663 nm and quantum yields of up to 87 %. Alternatively, borate complexes functionalized with p-tBuC₆H₄ or p-OMeC₆H₄ displayed fluorescence in the visible range that is not influenced by the nature of the solvent. Although the emission of the boranils was quenched in the solid state, HBBO borate complexes displayed intense fluorescence from 489 to 567 nm and quantum yields of up to 23 %. Finally, the excited states of a selection of borate complexes were modeled by using time-dependent DFT, which allowed calculation of the dipole moments of the dyes in their excited states.

Multidisciplinary research on novel organic luminescent dyes is propelled by potential applications in plastic electronics and biomedical sciences. The construction of sophisticated fluorescent dyes around a tetrahedral boron(III) center is a particular approach that has fueled the creativity of chemists. Success in this enterprise has been readily achieved with simple synthetic protocols, the products of which display unusual spectroscopic behavior. This account is a critical review of recent advances in the field of boron(III) complexes (excluding BODIPYs and acetylacetonate boron complexes) involving species displaying similar coordination features, and we outline their potential development in several disciplines.

The photophysical properties of a prototypic donor–acceptor dyad, featuring a conventional boron dipyrromethene (Bodipy) dye linked to a dicyanovinyl unit through a meso-phenylene ring, have been recorded in weakly polar solvents. The absorption spectrum remains unperturbed relative to that of the parent Bodipy dye but the fluorescence is extensively quenched. At room temperature, the emission spectrum comprises roughly equal contributions from the regular π, π* excited-singlet state and from an exciplex formed by partial charge transfer from Bodipy to the dicyanovinyl residue. This mixture moves progressively in favor of the locally excited π, π* state on cooling and the exciplex is no longer seen in frozen media; the overall emission quantum yield changes dramatically near the freezing point of the solvent. The exciplex, which has a lifetime of approximately 1 ns at room temperature, can also be seen by transient absorption spectroscopy, in which it decays to form the locally excited triplet state. Under applied pressure (P<170 MPa), formation of the exciplex is somewhat hindered by restricted rotation around the semirigid linkage and again the emission profile shifts in favor of the π, π* excited state. At higher pressure (170<P<550 MPa), the molecule undergoes reversible distortion that has a small effect on the yield of π, π* emission but severely quenches exciplex fluorescence. In the limiting case, this high-pressure effect decreases the molar volume of the solute by approximately 25 cm³ and opens a new channel for nonradiative deactivation of the excited-state manifold.

A set of linear and dissymmetric BODIPY-bridged push–pull dyes are synthesized. The electron-donating substituents are anisole and dialkylanilino groups. The strongly electron-accepting moiety, a 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) group, is obtained by insertion of an electron-rich ethyne into tetracyanoethylene. A nonlinear push–pull system is developed with a donor at the 5-position of the BODIPY core and the acceptor at the 2-position. All dyes are fully characterized and their electrochemical, linear and nonlinear optical properties are discussed. The linear optical properties of dialkylamino compounds show strong solvatochromic behavior and undergo drastic changes upon protonation. The strong push–pull systems are non-fluorescent and the TCBD-BODIPY dyes show diverse photochemistry and electrochemistry, with several reversible reduction waves for the tetracyanobutadiene moiety. The hyperpolarizability μβ of selected compounds is evaluated using the electric-field-induced second-harmonic generation technique. Two of the TCBD-BODIPY dyes show particularly high μβ (1.907 μm) values of 2050×10⁻⁴⁸ and 5900×10⁻⁴⁸ esu. In addition, one of these dyes shows a high NLO contrast upon protonation–deprotonation of the donor residue.

The synthesis, structural, and photophysical properties of a new series of original dyes based on 2-(2′-hydroxybenzofuran)benzoxazole (HBBO) is reported. Upon photoexcitation, these dyes exhibit intense dual fluorescence with contribution from the enol (E*) and the keto (K*) emission, with K* being formed through excited-state intramolecular proton transfer (ESIPT). We show that the ratio of emission intensity E*/K* can be fine-tuned by judiciously decorating the molecular core with electron-donating or -attracting substituents. Push–pull dyes 9 and 10 functionalized by a strong donor (nNBu₂) and a strong acceptor group (CF₃ and CN, respectively) exhibit intense dual emission, particularly in apolar solvents such as cyclohexane in which the maximum wavelength of the two bands is the more strongly separated. Moreover, all dyes exhibit strong solid-state dual emission in a KBr matrix and polymer films with enhanced quantum yields reaching up to 54 %. A wise selection of substituents led to white emission both in solution and in the solid state. Finally, these experimental results were analyzed by time-dependent density functional theory (TD-DFT) calculations, which confirm that, on the one hand, only E* and K* emission are present (no rotamer) and, on the other hand, the relative free energies of the two tautomers in the excited state guide the ratio of the E*/K* emission intensities.

La synthèse, les études structurales et photophysiques d’une nouvelle série de fluorophore basée sur une architecture 2-(2′-hydroxybenzofuran)benzoxazole (HBBO) sont décrites. Après photoexcitation, ces composés présentent une intense émission duale issue de l’émission simultanée des états excités des formes énol (E*) et kéto (K*). La forme K* est formée après un transfert de proton intramoléculaire dans l’état excité (ESIPT). Nous montrons que le ratio des intensités d’émission E*/K* peut être finement modulé par un choix judicieux de décoration sur le squelette moléculaire avec des substituents fortement donneur ou attracteur. Les colorants push–pull 9 et 10 fonctionnalisés par un donneur fort (nNBu₂) sur la partie phénol et un accepteur fort (CF₃ et CN respectivement) sur la partie benzoxazole présentent une émission duale intense, et ceci plus particulièrement dans des solvants apolaires tels que le cyclohexane, cas où la séparation entre les deux pics d’émission est la plus importante. Tous ces composés présentent en plus, une importante émission à l’état solide, que ce soit dans une matrice de KBr ou dans un film polymère, avec un rendement quantique de fluorescence allant jusqu’à 54 %. Une sélection pertinente de substituents permet d’obtenir une émission blanche en solution ou à l’état solide. Enfin, ces résultats expérimentaux ont été confirmés par TD-DFT (time-dependent density functional theory); ces études montrent non seulement que seules les émissions des espèces E* et K* sont présentes durant le processus (pas de rotamère), mais aussi que l’énergie libre relative des deux tautomères dans l’état excite guide le ratio des intensités d’émission E*/K*.

Thesynthesis of three red-emitting and water-soluble thienyl-BODIPYs has beenachieved. The trimethyl(propargyl)ammonium group was chosen as a vector forwater solubility. One or two cationic arms were introduced either on the2-position of the thienyl unit or on the 4-position on the boron atom. Thesedyes have pronounced absorption around 600 nm and intense emission at 650 nmwith quantum yield of about 60% in water. Grafting of such BODIPYs via a flexible arm to BSA is veryefficient, allowing attachment of 1 to 30 labels in a controlled manner.  Very strong fluorescence (quantum yield 56%)without aggregation of the dye at a low loading ratio (1:5 BSA/label) in PBSbuffer is measured.

Invited for the cover of this issue is the group of Raymond Ziessel at the University of Strasbourg. The image depicts the bright red fluorescence of a probe, both free in aqueous solution and when covalently linked to a model protein, such as BSA. Read the full text of the article at 10.1002/chem.201303988.

This article describes the multistep synthesis and photophysical properties of three highly fluorescent dyes based on the 2-(2′-hydroxyphenyl)benzoxazole (HBO) scaffold and their resulting chelation to a BF₂ fragment. These dyes possess functionalization at the 3,5-positions of the phenol ring with an ethynyl-extended fragment bearing TMS, p-tBuC₆H₄, or p-NnBu₂C₆H₄ groups. All of the new compounds were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. The optical properties of the HBO dyes reveal the presence of enol and keto bands as a result of a strong excited-state intramolecular proton transfer (ESIPT). This ESIPT process is highly dependent on the nature of the electronic substituents and the polarity of the solvent. Upon coordination to a BF₂ fragment, typical singlet emission is observed with λ_em ranging from 439 to 553 nm and quantum yields from 0.03 to 0.36. If aromatic amines are involved, strong aggregates are observed that could be dissociated upon protonation of the lone electron pair.

A series of thirteen luminescent tetrahedral borate complexes based on the 2-(2′-hydroxyphenyl)benzoxazole (HBO) core is presented. Their synthesis includes the incorporation of an ethynyl fragment by Sonogashira cross-coupling reaction, with the goal of extending the conjugation and consequently redshifting their emission wavelength. Different regioisomers, substituted in the 3-, 4-, or 5-position of the phenolate side of the HBO core, were studied in order to compare their photophysical properties. The complexes were characterized by X-ray diffraction and NMR, UV/Vis, and emission spectroscopy in solution and in the solid state. In all cases, complexation to boron leads to a donor–acceptor character that impacts their photophysical properties. Complexes with a 3- or 5-substituted fragment display mild to pronounced internal charge transfer (ICT), a feature strengthened by the presence of p-dibutylaminophenylacetylene in the molecular structure, protonation of the nitrogen atom of which leads to a significant blueshift and an increase in quantum yield. On the contrary, when the ethynyl module is grafted on the 4-position, narrow, structured, symmetrical absorption/emission bands are observed. Moreover, the fact that protonation has little effect on the emission maximum wavelength reveals singlet excited-state decay. Solid-state emission properties reveal a redshift compared to solution, explained by tight packing of the π-conjugated systems and the high planarity of the dyes. Subsequent connection of these complexes to other photoactive subunits (BODIPY, Boranil) provides dyads in which efficient cascade energy transfer is observed.

Cet article présente une série de treize complexes de bore tétraédriques luminescents basés sur le motif 2-(2′-hydroxyphenyl)benzoxazole (HBO). Leur synthèse comprend l’incorporation d’un fragment ethynyle par une réaction de couplage croisé de Sonogashira dans le but d’étendre la conjugaison et ainsi déplacer leur longueur d’onde d’émission dans le rouge (basses longueur d’onde). Différents régioisomères, substitués en position 3, 4 ou 5 du côté phénol du groupement HBO ont été étudiés afin de comparer leurs propriétés spectroscopiques. Les complexes ont été caractérisés par RMN, diffraction des rayons X sur mono-crystal, spectroscopie UV-Visible et émission à la fois en solution et à l’état solide. Pour chaque composé, la complexation au bore entraine un caractère donneur-accepteur de la molécule, ce va qui fortement influer sur les propriétés photophysiques. Les complexes fonctionnalisés en position 3 et 5 présentent un transfert de charge interne (TCI) qui est amplifié par la présence du groupement dibutylaminophénylacetylène dans la structure des molécules; la protonation de l’atome d’azote par de l’HCl gazeux entraine un déplacement de la longueur d’onde d’émission vers le bleu (longueur d’onde plus élevée) et une augmentation du rendement quantique. A l’opposé, lorsque l’espaceur éthynyle est greffé en position 4, des bandes d’absorption/émission étroites, structurées et symétriques sont observées. Par ailleurs, la protonation n’a que peu d’effet sur le maximum de la longueur d’onde d’émission, mettant en évidence une décroissance de l’état excité de type singulet. L’étude des propriétés d’émission à l’état solide révèlent un déplacement vers le rouge en comparaison des propriétés en solution, qui est expliqué par les empilements importants des systèmes conjugués et la grande planéité des colorants. La connexion de ces complexes à d’autres sous-unités photoactives (BODIPY, Boranil) permet d’obtenir des dyades où un transfert d’énergie en cascade est observé.

A series of new compounds in which various Bodipy dyes are grafted logically on triptycene rigid structures are synthesized and characterized, and their absorption spectra and photophysical properties are studied, also by pump-probe transient absorption spectroscopy. The studied compounds are: the mono-Bodipy species TA, TB, and TC (where A, B, and C identify different Bodipy subunits absorbing and emitting at different wavelengths), the multichromophore species TA₃, which bears three identical A subunits, and the three multichromophoric species TAB, TBC, and TABC, all of them containing at least two different types of Bodipy subunits. The triptycene moiety plays the role of a rigid scaffold, keeping the various dyes at predetermined distances and allowing for a three-dimensional structural arrangement of the multichromophoric species. The absorption spectra of the multichromophoric Bodipy species are essentially additive, indicating that negligible inter-chromophoric interaction takes place at the ground state. Luminescence properties and transient absorption spectroscopy indicate that a very fast (on the picosecond time scale) and efficient photoinduced energy transfer occurs in all the multi-Bodipy species, with the lower-energy Bodipy subunits of each multi-Bodipy compounds playing the role of an electronic energy collector. In TAB, an energy transfer from the A-type Bodipy subunit to the B-type one takes place with a rate constant of 1.6×10¹⁰ s⁻¹, whereas in TBC an energy transfer from the B-type Bodipy subunit to the C-type subunit is bi-exponential, exhibiting rate constants of 1.7×10¹¹ and 1.9×10¹⁰ s⁻¹; the possible presence of different conformers with different donor–acceptor distances in this bichromophoric species is proposed to cause the bi-exponential energy-transfer process. Interpretation of the intricate energy-transfer pathways occurring in TABC is made with the help of the processes identified in the bichromophoric compounds. In all cases, the measured energy-transfer rate constants agree with a Förster mechanism for the energy-transfer processes.

Une nouvelle séries de sondes Bodipy ont été construites sur une plateforme triptycene T préalablement fonctionnalisée. L’approche synthétique a consistée à construire d’abord un triptycene modifié avec trois Bodipy identiques TA₃ et à sélectivement transformer les unités existantes en des composés ayant des couleurs différentes (A, B, et C). De nombreux composés modèles ont ainsi pu être préparés tels que TA, TB, TC, TAB, TBC. La molécule cible TABC possède un ensemble de chromophores capable de transférer leur énergie sur la sonde de plus basse énergie et ses processus en cascade permettent de concentrer les photons sur un émetteur unique localisé à basse énergie. Le spectre d’absorption de TABC est une combinaison linéaire de l’absorption individuelle des quatre modules démontrant une faible interaction dans l’état fondamental. Les transferts d’énergie sont extrêmement rapides (picoseconde) et ont été étudiés par absorption transitoire. Plus précisément dans le modèle TAB le transfert d’énergie de A vers B a lieu en 60 ps tandis que le transfert de B vers C dans TBC se fait en 6 et 50 ps. La présence de différents conformères a été invoquée pour expliquer le déclin bi-exponentiel. L’interprétation des phénomènes de transfert d’énergie dans TABC a été faite à l’aide des composés modèles et donne une image réaliste de l’ensemble des processus impliqués lors d’une irradiation. L’ensemble de ces données sont en accord avec un transfert d’énergie par résonnance lié à une superposition spectrale de l’émission du donneur et de l’absorption de l’accepteur (théorie de Förster). Ces résultats montrent les progrès réalisables dans la concentration de photons et la monochromatisation de la lumière dans des molécules tridimensionnelles. Abstract in Italian: E’ stata sintetizzata e caratterizzata una nuova famiglia di antenne costituite da diversi frammenti cromoforici Bodipy ancorati su un core tripticenico. Sono stati studiati i loro spettri di assorbimento e le loro proprietà fotofisiche, anche tramite spettroscopia pump-probe di assorbimento transiente. Oltre ai sistemi multicromoforici TAB, TBC, e TABC (A, B, e C identificano differenti subunità Bodipy, che assorbono ed emettono a diversa energia) sono state preparate e studiate sia le specie modello monocromoforiche TA, TB e TC sia la specie multicromoforica TA₃, contenente tre Bodipy identici. Il frammento tripticenico ha il ruolo fondamentale di permettere un arrangiamento topologicamente controllato e rigido, nelle tre dimensioni, dei diversi cromofori. Gli spettri di assorbimento delle specie multicromoforiche sono essenzialmente additivi, indicando che allo stato fondamentale l′interazione intercromoforica è trascurabile. Le proprietà di luminescenza e la spettroscopia di assorbimento transiente hanno messo in evidenza che in tutti i sistemi multicromoforici investigati si verificano processi di trasferimento di energia elettronica fotoindotti, particolamente efficenti e veloci (nella scala temporale dei ps) verso la subunità a più bassa energia (trappola di energia) di ciascun sistema multi-Bodipy. In particolare, nel sistema TAB il trasferimento di energia dalla subunità di tipo A a quella di tipo B avviene con una costante di velocità pari a 1.6×10¹⁰ s⁻¹, mentre in TBC il trasferimento da B a C è biesponenziale, con costanti di velocità pari a 1.7×10¹¹ e 1.9×10¹⁰ s⁻¹. Tale comportamento potrebbe essere razionalizzato grazie alla presenza, per tale specie, di diversi conformeri con differenti distanze donatore - accettore. I risultati ottenuti per i sistemi bicromoforici hanno permesso di interpretare le complesse dinamiche di decadimento degli stati eccitati caratteristiche della specie multicromoforica TABC. Per tutte le specie investigate, i risultati ottenuti sperimentalmente sono in accordo con un meccanismo di trasferimento energetico fotoindotto di tipo Förster.

A small series of donor–acceptor molecular dyads has been synthesized and fully characterized. In each case, the acceptor is a dicyanovinyl unit and the donor is a boron dipyrromethene (BODIPY) dye equipped with a single styryl arm bearing a terminal amino group. In the absence of the acceptor, the BODIPY-based dyes are strongly fluorescent in the far-red region and the relaxed excited-singlet states possess significant charge-transfer character. As such, the emission maxima depend on both the solvent polarity and temperature. With the corresponding push–pull molecules, there is a low-energy charge-transfer state that can be observed by both absorption and emission spectroscopy. Here, charge-recombination fluorescence is weak and decays over a few hundred picoseconds or so to recover the ground state. Overall, these results permit evaluation of the factors affecting the probability of charge-recombination fluorescence in push–pull dyes. The photophysical studies are supported by cyclic voltammetry and DFT calculations.

New boron-dipyrromethene (BODIPY) dyes linked to viologen are prepared and their photophysical and electrochemical properties are investigated. Both synthesized molecules have similar electronic absorption spectra with the absorption maximum localized at 517 and 501 nm for dye 1 and dye 2, respectively. They exhibit well-defined redox behavior, highlighting the presence of BODIPY and viologen subunits, with little perturbation of the redox potential of both subunits with respect to the parent compounds. Both dyes are heavily quenched by photoinduced electron transfer from the BODIPY to the viologen subunit. The transient absorption technique demonstrates that dye 2 forms the viologen radical within a timeframe of 7.1 ps, and that the charge-separated species has a lifetime of 59 ps. Sustained irradiation of dye 2 in the presence of a tertiary amine allows for the accumulation of BODIPY–methyl-4,4′-bipyridinium (BODIPY–MV⁺), as observed by its characteristic absorption at 396 and 603 nm. However, dye 2 does not generate catalytic amounts of hydrogen under standard conditions.

Novel metal-free and fluorescent dipyrrolopyrrole (DPP) dyes consisting of a central bis(lactam)-bearing pendent benzyl or branched hydrocarbon groups as solubilizing fragments and two orthogonal side arms (dimethylaminopropyne and benzoate anion) have been designed and synthesized. The UV/Vis absorption spectra recorded in THF are dominated by intense low-energy π–π* absorptions centered at 488 nm or 602 nm, respectively, for the phenyl- or thiophene-based DPP dyes. The fluorescence spectra also display broad bands at 555 nm (Φ_F=0.57 and τ_F=4.6 ns) for the phenyl- and at 624 nm (Φ_F=0.31 and τ_F=3.5 ns) for the thiophene-based molecular structures. Under standard global AM 1.5G irradiation a maximum photon-to-electron conversion efficiency of 2.54 % was achieved with dye-sensitized solar cells based on nanocrystalline TiO₂ (J_sc=7.5 mA cm⁻², V_oc=0.49 V, and FF=0.70) for the phenyl-based DPP dye and 1.89 % (J_sc=7.1 mA cm⁻², V_oc=0.41 V, and FF=0.65) for the thiophene-based DPP dye.

A series of water-soluble red-emitting distyryl-borondipyrromethene (BODIPY) dyes were designed and synthesized by using three complementary approaches aimed at introducing water-solubilizing groups on opposite faces of the fluorescent core to reduce or completely suppress self-aggregation. An additional carboxylic acid functional group was introduced at the pseudo-meso position of the BODIPY scaffold for conjugation to amine-containing biomolecules/biopolymers. The optical properties of these dyes were evaluated under simulated physiological conditions (i.e., phosphate-buffered saline (PBS), pH 7.5) or in pure water. The emission wavelength (λ_max) of these labels was found in the 640–660 nm range with quantum yields from modest to unprecedentedly high values (4 to 38 %). The bioconjugation of these distyryl-BODIPY dyes with bovine serum albumin (BSA) and the monoclonal antibody (mAb) 12A5 was successfully performed under mild aqueous conditions.

De nouveaux colorants fluorescents à architecture distyrylborondipyrromethene (BODIPY), émettant dans le rouge et solubles dans l’eau, ont été préparés en utilisant trois méthodes efficaces de fonctionnalisation chimique qui permettent l’introduction de groupements hydrophiles (motifs pseudo-PEG et sulfonate) sur les parties nord et sud de leur squelette conjugué, et ce afin de réduire ou de supprimer totalement l’agrégation en solution aqueuse. La solubilité dans l’eau des fluorophores ainsi obtenus est élevée et leurs propriétés optiques en milieu physiologique remarquables et comparables à celles déterminées dans les solvants organiques pour les composés hydrophobes parents. De plus, la présence d’une fonction acide carboxylique en position méso de ces composés distyryl-BODIPY a permis le marquage covalent de protéines d’intérêt (albumine de sérum bovin et anticorps monoclonaux 12A5) via la formation de liens amide dans des conditions biocompatibles.

While acetylacetone (acacH) derivatives are, upon deprotonation, ubiquitous ligands in coordination chemistry, their potential to form stable ionic liquids has not been studied so far. Here we describe a straightforward synthesis of novel trifluoroacetylacetone-functionalised imidazolium salts. These salts are built from an imidazolium ring substituted on one side with a flexible chain of fixed length carrying a terminal acacH group and on the opposite side a paraffin chain of various lengths. By changing the length of these flexible chains (n=4, 8, 12) and the nature of the counter-anions (PF₆⁻, BF₄⁻, NTf₂⁻), room-temperature ionic liquids were produced. Their application for the extraction of lanthanide salts (Eu, Tb) from dilute aqueous solution has been investigated. The presence of a strong UV absorber (imidazolium ring, λ_abs=290 nm) allows photosensitisation of the Eu^III and Tb^III luminescence by efficient energy transfer, and thus extraction of these two lanthanides can be followed by fluorescence techniques. It appears that loading of the ionic liquids onto silica particles pre-treated with a dilute aqueous solution of NaOH is the most efficient way to obtain fast and almost quantitative (>99.9 %) extraction of the metal ions as their diketonato complexes. The procedure is reproducible and the loaded SiO₂ particles can be simply treated with acid to strip the metal ions and regenerate the adsorbed (protonated) extractant.

Synthetic strategies have been devised that allow the rational design and isolation of highly coloured boron dipyrromethene (BODIPY) dyes that absorb across much of the visible region. Each dye has an aryl polycycle (usually pyrene or perylene) connected to the central BODIPY core through a conjugated tether at the 3,5-positions. Both mono- and difunctionalised derivatives are accessible, in certain cases containing both pyrene and perylene residues. For all new compounds, the photophysical properties have been recorded in solution at ambient temperature and in a glassy matrix at 77 K. The presence of the aryl polycycle(s) affects the absorption and emission maxima of the BODIPY nucleus, thereby confirming that these units are coupled electronically. Indeed, the band maxima and oscillator strengths depend on the conjugation length of the entire molecule, whereas there is no sign of fluorescence from the polycycle. As a consequence, the radiative rate constant tends to increase with each added appendage. The nature of the linkage (styryl, ethenyl, or ethynyl) also exerts an effect on the photophysical properties and, in particular, the absorption spectrum is perturbed in the region of the aryl polycycle. The perylene-containing BODIPY derivatives absorb over a wide spectral range and emit in the far-red region in almost quantitative yield. A notable exception to this generic behaviour is provided by the anthracenyl derivative, which exhibits charge-transfer absorption and emission spectra in weakly polar media at ambient temperature. Regular BODIPY-like behaviour is restored in a glassy matrix at 77 K. Overall, these new dyes represent an important addition to the range of strongly absorbing and emitting reagents that could be used as solar concentrators.

We report on the synthesis, optical properties and energy-transfer features of a series of transition-metal-containing complexes and dyads, based on a pre-organised truxene scaffold. In this series, the [Ru(bpy)₃]²⁺ and [Os(bpy)₃]²⁺ photoactive terminals are coupled to the bridging aromatic truxene core through rigid ethynyl linkers. The photoinduced energy-transfer processes taking place from the Ru- to the Os-based levels, and from the truxene bridging ligand to the terminal-metal chromophores are studied and the pathways and mechanisms are discussed. The photoinduced energy-transfer process observed in the dyad proceeds rapidly through: i) an efficient ¹L¹Os direct energy transfer followed by intersystem crossing to ³Os, and ii) a fast ¹L¹Ru energy-transfer step and subsequent intersystem crossing to ³Ru followed by a ³Ru³Os energy-transfer process. The first ¹L¹Os and ¹L¹Ru steps are controlled by a dipole–dipole interaction (Förster mechanism), whereas the subsequent ³Ru³Os step proceeds by means of a long-range (≈24 Å) through-bond mediated Dexter mechanism, facilitated by the conjugation along the bpy-truxene-bpy molecular axis.

A series of modular mesogenic salts based on the combination of anionic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (F-BODIPY) 2,6-disulfonate dyes and trialkoxybenzyl-functionalised imidazolium cations has been designed and synthesised. Each salt contains a rigid dianionic BODIPY core associated with two imidazolium cations functionalised by 1,2,3-trialkoxybenzyl (alkyl=n-C₈, n-C₁₂ or n-C₁₆) units or, in one case, with imidazolium cations functionalised by a trialkylgallate (3,4,5-trialkoxybenzoate) unit in which the 3,5-dialkyl groups are terminated with a polymerisable acrylate entity. All these compounds were highly fluorescent in solution with quantum yields ranging from 54 to 62 %. In the solid state, the width of the emission band observed at around 650 nm is a clear signature of aggregation. With the trialkoxybenzylimidazolium cations, polarised optical microscopy (POM) and X-ray scattering experiments showed that columnar mesophases were formed. Differential scanning calorimetry (DSC) studies confirmed the mesomorphic behaviour from room temperature to about 130 °C for salts with alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of the BODIPY unit was maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The salt containing the gallate-functionalised imidazolium cations showed no mesomorphism but the acrylate terminal units could be used to engender photoinitiated polymerisation thereby allowing the material to be immobilised on glass plates. The polymerisation process was followed by FTIR spectroscopy and the fixed and patterned films were highly fluorescent with a solid-state emission close to that of the complex in the solid state.

A series of novel multichromophoric, luminescent compounds has been prepared, and their absorption spectra, luminescence properties (both at 77 K in rigid matrix and at 298 K in fluid solution), and photoinduced intercomponent energy-transfer processes have been studied. The series contains two new multichromophoric systems 1 and 2, each one containing two different boron–dipyrromethene (Bodipy) subunits and one bridging fluorene species, and two fluorene–Bodipy bichromophoric species, 6 and 7. Three monochromophoric compounds, 3, 4, and 5, used as precursors in the synthetic process, were also fully characterized. The absorption spectra of the multichromophoric compounds are roughly the summation of the absorption spectra of their individual components, thus demonstrating the supramolecular nature of the assemblies. Luminescence studies show that quantitative energy transfer occurs in 6 and 7 from the fluorene chromophore to the Bodipy dyes. Luminescence studies, complemented by transient-absorption spectroscopy studies, also indicate that efficient inter-Bodipy energy transfer across the rigid fluorene spacer takes place in 1 and 2, with rate constants, evaluated by several experimental methods, between 2.0 and 7.0×10⁹ s⁻¹. Such an inter-Bodipy energy transfer appears to be governed by the Förster mechanism. By taking advantage of the presence of various protonable sites in the substituents of the lower-energy Bodipy subunit of 1 and 2, the effect of protonation on the energy-transfer rates has also been investigated. The results suggest that control of energy-transfer rate and efficiency of inter-Bodipy energy transfer in this type of systems can be achieved by an external, reversible input.

We have designed and synthesised a series of modular, mesogenic complexes based on anthracene-2,6-disulfonate and trialkoxybenzyl-functionalised imidazolium cations. Each complex contains a central, rigid, dianionic anthracene core and two flexible monocations bearing paraffin chains anchored on imidazolium rings. Anthracene-2,6-disulfonate can be crystallised with various simple alkylammonium ions and, in the case of ⁺N(CH₃)₂(C₁₆H₃₃)₂, a crystal structure determination has shown that the long paraffinic chains are intercalated between the anthracene moieties. The dianion forms columnar mesophases with trialkoxybenzylimidazolium cations, as identified by polarising optical microscopy and X-ray scattering measurements. Differential scanning calorimetry studies confirmed mesomorphic behaviour from room temperature to about 200 °C for alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of anthracene is maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The new functional materials described herein provide an easy access to stable and luminescent mesomorphic materials engineered by an ionic self-assembly process.

Une nouvelle série de complexes mésogènes obtenus par association électrostatique entre l’anthracène-2,6-disulfonate et des imidazoliums fonctionnalisés a été synthétisée. Les propriétés optiques et d’auto-organisation de ces complexes, constitués d’un noyau rigide central dianionique d’anthracène et de deux cations flexibles à cœur imidazolium, ont été étudiées. Associé à des dérivés d’ammoniums portant de longues chaînes carbonées, l’anthracène-2,6-disulfonate peut être cristallisé et la structure obtenue avec la cation ⁺N(CH₃)₂(C₁₆H₃₃)₂ montre qu’il n’y a pas de ségrégation entre les chaînes grasses et le cœur rigide du dérivé d’anthracène. Par contre, associé à des imidazoliums fonctionnalisés par des dérivés tris-alkoxybenzyl, une microségrégation peut être engendrée et des mésophases colonnaires ont pu être observées et identifiées par POM ainsi que par diffraction aux rayons X. Des études par calorimétrie différentielle à balayage (DSC) confirme le comportement mésomorphe des complexes sur une large gamme de température s’étalant de 20°C à 200°C avec des chaînes alkyles à 8, 12, 16 atomes de carbone. Les propriétés de luminescence de l’anthracène sont maintenues au sein des mésophases et des études par spectroscopie d’émission confirment la présence d’agrégat de type J entre les fragments aromatiques. Ces nouveaux complexes fonctionnels, obtenus par auto-assemblage par voie électrostatique, fournissent un accès rapide et simple à des matériaux mésomorphes et luminescents. Abstract in Spanish: Hemos diseñado y sintetizado una serie de complejos mesógenos modulares basados en antraceno-2,6-disulfonato y cationes imidazolio funcionalizados con tris(alcoxi)bencilo. Todos los complejos contienen un núcleo central rígido dianiónico de antraceno y dos monocationes flexibles que portan cadenas parafínicas ancladas en los anillos de imidazol. El antraceno-2,6-disulfonato puede cristalizarse con varios iones alquilamonio simples y, en el caso de ⁺N(CH₃)₂(C₁₆H₃₃)₂, la determinación de la estructura cristalina ha mostrado que las cadenas parafínicas largas están intercaladas entre las unidades de antraceno. Con los cationes tris(alcoxi)bencilimidazolio, el dianión forma mesofases columnares identificadas por medidas de microscopía óptica con luz polarizada y difracción de rayos X. Los estudios de DSC confirman el comportamiento mesomorfo desde temperatura ambiente hasta 200ºC para cadenas alquílicas que contienen 8, 12 y 16 átomos de carbono. La fuerte luminiscencia del antraceno se mantiene en la mesofase y las medidas de fluorescencia confirman la presencia de agregados J en todos los casos. Los nuevos materiales funcionales descritos aquí representan un fácil acceso a materiales mesomorfos luminiscentes estables generados por un proceso de auto-ensamblaje iónico.