Photophysical and structural properties of cyanoruthenate complexes of hexaazatriphenylene

The tritopic bridging ligand hexaazatriphenylene (HAT) has been used to prepare the mono-, di-, and trinuclear cyanoruthenate complexes [Ru(CN)(4)(HAT)](2-) ([1](2-)), [{Ru(CN)(4)}(2)(mu(2)-HAT)](4-) ([2](4-)), and [{Ru(CN)(4)}(3)(mu(3)-HAT)](6-) ([3](6-)). These complexes are of interest both for their photophysical properties and ability to act as sensitizers, associated with strong MLCT absorptions; and their structural properties, with up to 12 externally directed cyanide ligands at a single "node" for preparation of coordination networks. The complexes are strongly solvatochromic, with broad and intense MLCT absorption manifolds arising from the presence of low-lying pi* orbitals on the HAT ligand, as confirmed by DFT calculations; in aprotic solvents [3](6-) is a panchromatic absorber of visible light. Although nonluminescent in fluid solution, the lowest MLCT excited states have lifetimes in D(2)O of tens of nanoseconds and could be detected by time-resolved IR spectrosocopy. For dinuclear [2](4-) and trinuclear [3](6-) the TRIR spectra are indicative of asymmetric MLCT excited states containing distinct Ru(III) and Ru(II) centers on the IR time scale. The complexes show red (3)MLCT luminescence as solids and in EtOH/MeOH glass at 77 K. Ln(III) salts of [1](2-), [2](4-), and [3](6-) form infinite coordination networks based on Ru-CN-Ln bridges with a range of one-, two-, and three-dimensional polymeric structures. In the Yb(III) and Nd(III) salts of [3](6- )the complex anion forms an 8-connected node. Whereas all of the Gd(III) salts show strong (3)MLCT luminescence in the solid state, the Ru-based emission in the Nd(III) and Yb(III) analogues is substantially quenched by Ru --> Ln photoinduced energy transfer, which results in sensitized near-infrared luminescence from Yb(III) and Nd(III).     

Synthesis and photophysical properties of soluble polyimides and polyquinazolones containing side-chain chalcones or azo chromophores

Soluble aromatic and carboxyl- and hydroxyl-containing polyimides, mixed polyimides, and polyquinazolones of various chemical structures, as well as a series of new dicyanoazobenzene chromophores, are synthesized. From 20 to 80 mol % of chromophore groups are incorporated into side chains of the polymers. The thermal, photosensitive, and nonlinear optical properties (second-harmonic generation) of the chromophore-containing polymers are investigated. The polymers with covalently attached groups of the dye DR-13 or azo-derivatives of 4-phthalonitrile demonstrate the highest nonlinearity. The T _g values of the polyimides vary from 165 to 215°C; their temperatures corresponding to 5% weight loss lie in the range 290–350°C; and the measured coefficients of second-harmonic generation, d ₃₃, for a number of polarized films based on chromophore-containing polymers attain several tens of picometers per volt. The incorporation of chromophore groups into the side chains of the polymers causes an increase in the photosensitivity of polyimides by an order of magnitude relative to that of the parent polymers (S _0.1 = (3?4) × 10⁵ cm²/J in the range of dye absorption).     

Synthesis and photophysical properties of novel pyrimidine-based two-photon absorption chromophores

Three new two-photon absorption chromophores based on a pyrimidine core were synthesized by Aldol condensation in the absence of any organic solvents. Their single-photon spectroscopic characterization as well as their two-photon absorption properties is reported. In addition, strong modulation of single-photon and two-photon fluorescent spectra of these molecules by (de)protonation is also discussed.     

Nonlinear optical properties of some side chain copolymers based on benzoxazole containing chromophores

Acrylate‐methylmethacrylate copolymers have been synthesized for nonlinear optical applications. Acrylate monomer units are characterized by the presence in the side chain of phenylbenzoxazole groups containing electron donor‐electron acceptor substituents. The phase behavior of all polymers has been investigated by DSC, X‐ray diffraction and polarizing microscopy: two of them exhibit liquid crystalline behavior of smectic type. For four polymers, nonlinear optical properties have been examined by second harmonic generation measurements on thin films (∼ 1 μm thickness) electrically poled by corona discharge. Second order susceptibility coefficients d₃₃ and average relaxation times 〈τ〉, relative to the time stability of the chromophore poling, have been measured. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 603–608, 1999     

新型双光子吸收化合物的合成、光物理及其在固态分散体系中的性质

通过多步反应制备了三个新型的双光子吸收化合物,测试了它们的光物理性质,发现该系列化合物具有较大的双光子吸收截面,并且随温度降低其双光子吸收截面增大.尤其是化合物TMVDB,其量子效率为0.83,常温时的双光子吸收截面达到1164GM,其双光子吸收截面除以分子量为2.08,表现出了优良的双光子吸收发光性能.进一步将TMVDB掺杂到固体材料中,得到强双光子诱导发光的固体材料.     

Effects of (multi)branching of dipolar chromophores on photophysical properties and two-photon absorption

To investigate the effect of branching on linear and nonlinear optical properties, a specific series of chromophores, epitome of (multi)branched dipoles, has been thoroughly explored by a combined theoretical and experimental approach. Excited-state structure calculations based on quantum-chemical techniques (time-dependent density functional theory) as well as a Frenkel exciton model nicely complement experimental photoluminescence and one- and two-photon absorption findings and contribute to their interpretation. This allowed us to get a deep insight into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved. Both experiment and theory reveal that a multidimensional intramolecular charge transfer takes place from the donating moiety to the periphery of the branched molecules upon excitation, while fluorescence stems from an excited state localized on one of the dipolar branches. Branching is also observed to lead to cooperative enhancement of two-photon absorption (TPA) while maintaining high fluorescence quantum yield, thanks to localization of the emitting state. The comparison between results obtained in the Frenkel exciton scheme and ab initio results suggests the coherent coupling between branches as one of the possible mechanisms for the observed enhancement. New strategies for the rational design of NLO molecular assemblies are thus inferred on the basis of the acquired insights.     

Absorption spectra, photophysical properties, and redox behavior of ruthenium(II) polypyridine complexes containing accessory dipyrromethene-BF2 chromophores

The six multichromophoric species 1-6, containing the potentially luminescent Ru(II) polypyridine subunits and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene fluorophores (dipyrromethene-BF(2) dyes, herein after called bodipy), have been prepared and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox properties have been investigated (for the structuralformulas of all the compounds, see Figure 1). For comparison purposes, also the same properties of the bodipy-based free ligands have been examined. Three of the multichromophoric species (1-3) are based on the Ru(bpy)(3)-type metal subunit, whereas 4-6 are based on the Ru(terpy)(2)-type metal subunit. Transient absorption spectroscopy at room temperature of all the compounds has also been performed. The absorption spectra of all the metal complexes show features that can be assigned to the Ru(II) polypyridine subunits and to the bodipy centers. In particular, the lowest energy spin-allowed pi-pi* transition of the bodipy groups dominates the visible region, peaking at about 530 nm. All the new complexes exhibit a rich redox behavior, with reversible processes attributed to specific sites, indicating a small perturbation of each redox center and therefore highlighting the supramolecular nature of the multichromophoric assemblies. Despite the good luminescence properties of the separated components, 1-6 do not exhibit any luminescence at room temperature; however, transient absorption spectroscopy evidences that for all of them a long-lived (microsecond time scale) excited state is formed, which is identified as the bodipy-based triplet state. Pump-probe transient absorption spectroscopy suggests that such a triplet state is formed from the promptly prepared bodipy-based (1)pi-pi* state in most cases by the intervention of a charge-separated level. At 77 K, all the complexes except complex 1 exhibit the bodipy-based fluorescence, although with a slightly shortened lifetime compared to the corresponding free ligand(s), and 4-6 also exhibit a phosphorescence assigned to the bodipy subunits. Phosphorescence of bodipy species had never been reported in the literature to the best of our knowledge: in the present cases we propose that it is an effective decay process thanks to the presence of the ruthenium heavy atom and of the closely lying (3)MLCT state of the Ru(terpy)(2)-type subunits.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Boron-containing two-photon-absorbing chromophores. 3. One- and two-photon photophysical properties of p-carborane-containing fluorescent bioprobes

Boron-containing two-photon-absorbing fluorophores have been prepared as new bifunctional molecules, potentially useful in two-photon excited microscopy (TPEM) and boron neutron capture therapy. They are based on a one-dimensional conjugated system containing a p-carborane entity at one end of the molecule and various electron-donating groups containing oxygen or nitrogen atoms at the other end. We investigated their one- and two-photon photophysical properties. They showed efficient fluorescence in an organic solvent, as well as in water for two of them, allowing microscopy on cell cultures. High two-photon absorption cross sections were determined in the 700-900 nm range. TPEM images were obtained with these new p-carborane-containing fluorophores, with laser intensities in the submilliwatt range.     

Theoretical study of the effects of solvent environment on photophysical properties and electronic structure of paracyclophane chromophores

We use first-principles quantum-chemical approaches to study absorption and emission properties of recently synthesized distyrylbenzene (DSB) derivative chromophores and their dimers (two DSB molecules linked through a [2.2]paracyclophane moiety). Several solvent models are applied to model experimentally observed shifts and radiative lifetimes in Stokes nonpolar organic solvents (toluene) and water. The molecular environment is simulated using the implicit solvation models, as well as explicit water molecules and counterions. Calculations show that neither implicit nor explicit solvent models are sufficient to reproduce experimental observations. The contact pair between the chromophore and counterion, on the other hand, is able to reproduce the experimental data when a partial screening effect of the solvent is taken into account. Based on our simulations we suggest two mechanisms for the excited-state lifetime increase in aqueous solutions. These findings may have a number of implications for organic light-emitting devices, electronic functionalities of soluble polymers and molecular fluorescent labels, and their possible applications as biosensors and charge/energy conduits in nanoassemblies.     

Strong two photon absorption and photophysical properties of symmetrical chromophores with electron accepting edge substituents

Two photon absorption (TPA) and photophysical properties of three new symmetrical chromophores with electron accepting phthalimide edge substituents have been studied. The three chromophores contain fluorene, alcoxy-substituted divinyl benzene, and carbazole moieties as central cores, respectively. The femtosecond time-resolved fluorescence upconversion spectroscopy and two photon excited fluorescence technique have been carried out. The effect of solvent polarity on TPA and on photophysics has also been determined. Ultrafast fluorescence dynamics, with decay times ranging from 1 to 13 ps, are revealed in polar solvents. This is attributed to the relaxation of the chromophores to the intramolecular charge transfer state. The chromophore bearing fluorene central core, being of the type A-pi-A, is the most efficient concerning TPA. Strong TPA, with a cross section value as high as 2100 GM at an excitation wavelength of 770 nm is found in acetophenone which is a solvent of intermediate polarity. The TPA spectra were also reproduced using a sum over states three-state model. A study of the TPA induced photobleaching of the fluorene molecule, doped in a solid poly(methyl-methacrylate) film, has shown that this material is very promising for efficient TPA optical data storage.     

Two novel terpyridine-based chromophores with donor-acceptor structural model containing modified triphenylamine moiety: Synthesis, crystal structures and two-photon absorption properties

Two novel terpyridine-based chromophores with D-A (D = donor, A = acceptor) structural model containing modified triphenylamine moiety (L1 and L2 ) have been conveniently synthesized via formylation and reduction in satisfactory yields, and fully characterized. The single crystals of them were obtained and determined by X-ray diffraction analysis. The relationships between structure and photophysical properties of the two chromophores were investigated both experimentally and theoretically. The measured maximum TPA cross-sections per molecular weight (δmax /MW) of the chromophores are 0.63 GM/(g mol) (L1) and 0.72 GM/(g mol) (L2), respectively, in DMF as a high polar solvent. The results indicate that the value of δmax/MW could be well tuned by the intramolecular charge transfer (ICT), which could be realized by introducing additional elecron-donor/acceptor groups.     

Vinyl copolymers containing pendant 1,3,4-oxadiazole chromophores: Preparation and electrochemical and electroluminescent properties

Three vinyl copolymers (P1–P3) containing pendant aromatic 1,3,4-oxadiazole derivatives were prepared from their precursor poly(styrene-ran-4-vinylbenzyl chloride) (weight-average molecular weight = 11,400, polydispersity index = 1.18), which had been synthesized by controlled radical polymerization (reversible addition–fragmentation chain transfer). The copolymers were readily soluble in common organic solvents and were basically amorphous materials with 5% weight loss temperatures higher than 360°C. The photoluminescence spectroscopy results revealed that the architectures of P2 and P3 suppressed aggregate formation in the solid state. The LUMO levels of P2 (−3.10 eV) and P3 (−3.09 eV), estimated from cyclic voltammetry data, were much higher than that of P1 (−3.81 eV). The HOMO levels were in the order of P3 (−5.37 eV) > P2 (−5.77 eV) > P1 (−5.96 eV). However, both the HOMO and LUMO levels of P1–P3 were much lower than that of poly[2-methoxy-5-(2′-ethylhexoxy)-p-phenylenevinylene] (MEH-PPV) because of the electron-withdrawing characteristics of the pendant aromatic 1,3,4-oxadiazole groups. The luminance (5860 cd/m²) and current efficiency (1.45 cd/A) of an electroluminescence device [indium tin oxide/poly(3,4-ethylene dioxythiophene)/MEH-PPV/Al] were improved significantly to 16,261 cd/m² and 4.79 cd/A, respectively, through blending with P2 (50/50). This study suggests that copolymers P1–P3 are versatile materials for electron-transport/injection applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2259–2272, 2007     

Elaboration of covalently linked polyoxometalates with ruthenium and pyrene chromophores and characteriation of their photophysical properties

Keggin and Dawson-type polyoxometalates (POMs) decorated by organometallic [cyclometalated ruthenium(II) polypyridine complex] or organic (pyrene) chromophores were prepared by postfunctionalization of hybrid disilylated POM platforms. The connection is made in a very efficient and modular way via Sonogashira coupling reactions, which provide a rigid linkage between the POM and the photoactive centers. Electronic properties have been inferred from electrochemical and photophysical studies and reflect poor electronic interactions between both partners. The presence of the POM leads to luminescence quenching of the chromophores, which was attributed to an intramolecular electron transfer from the chromophore to the POM. The rate of this process is much faster in the POM-pyrene than in the POM-Ru system. It depends on the driving force dictated by the redox potentials of both partners but also in the case of the POM-Ru system on the presence of the metallacycle, which acts as a molecular insulator and delays the intramolecular electron transfer. In the POM-Ru system, a comparative study of the luminescence quenching showed that the electron transfer is still more important in the covalently bonded hybrids than in systems where the POM and the ruthenium complexes are assembled via electrostatic interactions.     

Bipolar molecules with high triplet energies: synthesis, photophysical, and structural properties

This article sheds new light on the interplay of electronic and conformational effects in luminescent bipolar molecules. A series of carbazole/1,3,4-oxadiazole hybrid molecules is described in which the optoelectronic properties are systematically varied by substituent effects which tune the intramolecular torsion angles. The synthesis, photophysical properties, cyclic voltammetric data, X-ray crystal structures, and DFT calculations are presented. Excited state intramolecular charge transfer (ICT) is observed from the donor carbazole/2,7-dimethoxycarbazole to the acceptor phenyl/diphenyloxadiazole moieties. Introducing more bulky substituents onto the diphenyloxadiazole fragment systematically increases the singlet and triplet energy levels (E(S) and E(T)) and blue shifts the absorption and emission bands. The triplet excited state is located mostly on the oxadiazole unit. The introduction of 2,7-dimethoxy substituents onto the carbazole moiety lowers the value of E(S), although E(T) is unaffected, which means that the singlet-triplet gap is reduced (for 7bE(S) - E(T) = 0.61 eV). A strategy has been established for achieving unusually high triplet levels for bipolar molecules (E(T) = 2.64-2.78 eV at 14 K) while at the same time limiting the increase in the singlet energy.     

Arylethynylacridines: electrochemiluminescence and photophysical properties

Electrogenerated chemiluminescence (ECL) of six new ethyne-based acridine derivatives (1-6) has been studied. The new acridine derivatives were synthesized by cross-coupling of 9-chloroacridine and corresponding donor-substituted phenylethynes under modified Sonogashira conditions. The donor groups were varied in the order of increasing steric hindrance and donor strength at the donor site. The solution phase photophysical properties and ECL of these compounds were studied comparatively in acetonitrile solvent. The UV-Visible spectra of compounds 1-5 exhibit closely the same maxima. Density functional theory (DFT) has been invoked to analyze and understand the unexpected UV-Visible absorption behavior. Compounds with weak electron donors produce excimer ECL irrespective of steric hindrance at the donor site, while the compound with a stronger donor gives rise to ECL that is blue-shifted with respect to its photoluminescence spectrum. All except one of these compounds also exhibit solid state fluorescence which may be useful for solid state devices such as organic light emitting diodes (OLEDs) and as laser dyes. The observed properties are discussed with reference to the structure of the compounds synthesized.     

Synthesis and photophysical properties of highly emissive compounds containing a dibenzosilole core

A series of new rigid rod-like molecules consisting of a dibenzosilole core, ethynylene linkages, and different aryl end-groups has been synthesized by palladium-catalyzed Sonogashira cross-coupling reactions. These compounds exhibit intense blue to green emissions with high quantum efficiencies and good thermal stabilities.     

Self-assembling and photophysical properties of the organogelators based on cyanostyryl-substituted carbazoles

Four cyanostyryl-substituted carbazole derivatives (CN-ODEC1, CN-ODEC2, CN-DDEC1, and CN-DDEC) were synthesized and their self-assembly properties have been studied. It was found that they could form organogels especially in aromatic solvents. Scanning electron microscopy and light microscopy images show that the xerogels formed from monosubstituted derivatives (CN-O/DDEC1) gave well-organized tapes, and those from disubstituted derivatives (CN-O/DDEC2) exhibited heavy entangled three-dimensional structures. The UV–vis absorption and fluorescence emission spectra, as well as X-ray diffraction patterns, suggest that carbazole derivatives underwent J-type π-stacking. Meanwhile, we suggested that strong H-bonding and moderate π–π interactions were the key driving force for the gelation of the monosubstituted derivatives, and head-to-tail “ladder-type” J-aggregates were formed in the gel state. On the other hand, strong π–π interaction might be considered as the main driving force for the gelation of disubstituted derivatives, and J-aggregates with no well-organized packing mode of molecules were obtained in the gel phase. It should be noticed that aggregation-induced emission was observed during the gelation processes.     

Donor-functionalized polydentate pyrylium salts and phosphinines: synthesis, structural characterization, and photophysical properties

A series of donor-functionalized pyrylium salts have been prepared by classical condensation reactions which were further converted into the corresponding thienyl- and pyridyl-substituted polydentate lambda(3)-phosphinines by reaction with P(SiMe(3))(3). Further chemical modification of these phosphorus heterocycles with Hg(OAc)(2) in the presence of methanol resulted in the formation of lambda(5)-phosphinines. The photophysical properties of a selected series of thienyl- and pyridyl-functionalized pyrylium salts, lambda(3)- and lambda(5)-phosphinines, were investigated and the results compared and supported by theoretical calculations on the DFT level. Significant fluorescence was observed for the pyrylium salts and lambda(5)-phosphinines. In contrast, the heteroaromatic substituted lambda(3)-phosphinines show very little emission which is consistent with the low oscillator strength predicted by DFT calculations for this pi-->pi* transition. Furthermore, all three classes of compounds show readily observable phosphorescence in solution, which was determined by time-gated detection at low temperature.     

Molecular wires based on thienylethynylene: synthesis, photophysical properties, and excited-state lifetime

A series of pi-conjugated molecular wires based on thienylethynylene units have been developed to understand the effect of the molecular structures on their photophysical properties. The investigation of their photophysical properties indicates that the formation of aggregates at the ground state is effectively suppressed by the incorporation of truxene units. The excited-state lifetimes are observed to be biexponential for these molecular wires.