Synthesis and optical properties of unsymmetrical conjugated dendrimers focally anchored with perylenes in different geometries

Two sets of light-harvesting monodendrons with unsymmetrical conjugated phenylacetylene branches and perylene cores, one with pi-conjugation from the branches to the core and one without, were synthesized and their photophysical properties were studied by steady-state and time-resolved spectroscopic methods. These monodendrons show comparably high fluorescence quantum yields and efficient energy-transfer properties.     

Synthesis and optical properties of conjugated dendrimers with unsymmetrical branching

An improved synthetic approach to conjugated monodendrons with unsymmetrical branching structures is reported. Dendrimers containing two or three such conjugated monodendrons are synthesized and their optical properties are studied. Such dendrimers exhibit broad absorptions and very high fluorescence quantum yields, making them promising candidates for applications in molecular-based photonics.     

Energy transfer in unsymmetrical phenylene ethynylene dendrimers

We have applied the fluorescence upconversion technique to explore the electronic excitation energy transfer in unsymmetrical phenylene ethynylene dendrimers. Steady-state emission spectra show that the energy transfer from the dendrons to the core is highly efficient. Ultrafast time-resolved fluorescence measurements are performed at various excitation wavelengths to explore the possibility of assigning absorption band structures to exciton localizations. We propose a kinetic model to describe the time-resolved data. Independent of the excitation wavelength, a typical rise-time value of 500 fs is measured for the fluorescence in the dendrimer without an energy trap, indicating initial delocalized excitation. While absorption is into delocalized exciton states, emission occurs from localized states. When an energy trap such as perylene is introduced on the dendrimer, varying the excitation wavelength yields different energy-transfer rates, and the excitation energy migrates to the trap through two channels. The interaction energy between the dendrimer backbone and the trap is estimated to be 75 cm(-1). This value is small compared to the vibronic bandwidth of the dendrimer, indicating that the monodendrons and the energy trap are weakly coupled.     

Phenylacetylene Dendrimers Containing a Fluorene Core: Synthesis and Spectroscopic Studies

Phenylacetylene dendrimers 9 – 11 containing fluorene as the core with a larger HOMO‐LUMO energy gap were synthesized and characterized. Their structure and properties were studied by UV, FL, ¹H NMR, MS etc. These novel phenylacetylene dendrimers exhibit unique photophysical properties. They exist a new absorption band around 340 nm whose molar coefficient decreases with increasing generation. The band‐gaps of 9 – 11 are 3.54, 3.43 and 3.02 respectively. The fluorescence quantum yield of 10 is as high as 0.61.     

Synthesis of light-harvesting dendrimers focally anchored with crown ethers or terpyridine ligands

Crown ethers and terpyridine ligands have been successfully attached to the focal point of light harvesting phenylacetylene monodendrons through Pd-catalyzed coupling reactions. The structures of these functional monodendrons were characterized by 1H and 13C NMR spectroscopy, mass spectrometry and elemental analysis. Such binding-ligand anchored dendrons exhibit broad absorption, large molar extenction coefficients and high fluoresence quantum yields. Coordination of crown ethers with alkali ions results in a significant increase in absorption strength in the UV range, but little alteration in either intensity or position of fluorescence emission. Coordination of terpyridine ligands with Ru2+, however, does efficiently quench the fluorescence from the dendrons,albeit only the smallest dendron exhibits efficient binding.     

Polyaryl ether dendrimer with a 4-phenylacetyl-5-pyrazolone-based terbium(III) complex as core: synthesis and photophysical properties

A series of novel dendritic beta-diketone ligands, 1-phenyl-3-[G-n]-4-phenylacetyl-5-pyrazolone (n = 0-3, G stands for polyaryl ether), were synthesized by introducing Fréchet-type dendritic branches. The corresponding Tb3+-cored dendritic complexes were characterized by X-ray crystallography, elemental analysis, ESI mass spectra, and FT-IR spectra. These dendritic complexes, prepared from aqueous solution, exhibit high stability. Interestingly, the study of photophysical properties shows that the luminescence quantum yields of the dendritic Tb-complexes increase from 0.1 to 2.26% with an increase of the dendritic generation from 0 to 3. Importantly, an "energy-reservoir effect" was observed in the dendritic system using the method based on the resonance energy transfer from these complexes to rhodamine 6G. With the increase of the dendritic generation, the metal-centered luminescence quantum yield was almost the same, and the energy transfer (phi(transfer)) from the ligand to Tb(3+) increased. Further measurements of the triplet state and oxygen quenching of these dendritic complexes verify that this enhancement of the energy transfer (phi(transfer)) is attributed to both an "antenna effect" and a "shell effect".     

Spontaneously bundled nanotubes exhibit greatly enhanced emission via inter-nanotube energy transfer

Spontaneously bundled nanotubes assembled from chiral perylene diimide molecules exhibit greatly enhanced emission via inter-nanotube excitation energy transfer. The formation of densely packed superstructures is an effective approach for high fluorescence quantum yield in assembled nanomaterials without compromising optoelectronic properties.     

树枝形聚合物修饰双8-羟基喹啉衍生物的合成及稳态光物理性质研究

设计合成了1 3代芳醚骨架树枝形聚合物修饰的双8 羟基喹啉衍生物.对这些化合物在不同溶剂中的荧光光谱研究表明,随着代数的增加,目标树枝形聚合物的荧光量子产率增大,树枝形聚合物对核心发色团具有一定的隔离作用,并且目标分子内可以发生从骨架向核心发色团的能量传递.     

On/off switching of perylene tetracarboxylic bisimide luminescence by means of substitution at the N-position by electron-rich mono-, di-, and trimethoxybenzenes

A series of perylene tetracarboxylic bisimides, substituted at the N-position with methoxyphenyl groups, have been synthesized together with model compounds and their photophysical properties have been investigated by means of steady-state and time-resolved spectroscopic techniques. The luminescence properties of the examined compounds vary remarkably with the substitution pattern, with emission quantum yields ranging from 1 to 10(-2)-10(-3). The observed quenching of the luminescence is assigned to a photoinduced electron transfer (PET) from the electron-rich methoxybenzene unit to the perylene bisimide moiety. The radical anion of perylene bisimide has been detected by transient-absorption spectroscopy. The results could satisfactorily be explained by taking into consideration the redox potentials of the partners and the electron-releasing ability of each methoxy group in relation to its position with respect to N. Quantum-chemical calculations were also performed.     

Synthesis of phenothiazine-functionalized porphyrins with high fluorescent quantum yields

Two porphyrins with oligo-phenothiazine arms have been synthesized by a combination of Heck and Adler reaction, and their photophysical properties have been investigated by absorption and steady-state fluorescence spectroscopy. It is found that the excitation energy transfer occurs from the phenothiazine units to the porphyrin core, and that the porphyrins can emit intense red light with high fluorescent quantum yields.     

Synthesis and Self‐Assembly of Dihydroxyperylene Bisimides for the Tuning of Photophysical Properties

The synthesis of 1,10‐dihydroxyperylene bisimides by nucleophilic substitution of brominated perylene bisimide is described. 1,10‐Dihydroxyperylene bisimides formed J aggregates in nonpolar solvents and showed a clearly redshifted absorption band. The solvent polarity also influenced the hydrogen bond with the hydroxyl group, and thus, the photophysical properties of perylene bisimide. The photophysical properties of these dihydroxyperylene perylene bisimides can also be tuned by changing charge transfer from the hydroxyl groups to the perylene core through the introduction of metal ions.     

Synthesis and photophysical properties of chiral dendrimers with quinoline surface group via click chemistry

Synthesis of some novel chiral dendrimers containing quinoline as surface group and 1,2,3-triazole as branching unit is described. The chiroptical property exhibits the widening of the torsional angle in the BINOL core as the generation increases. The photophysical properties indicate an increase in the molar extinction coefficient and fluorescence intensity and a decrease in quantum yield and lifetime as the generation of the dendrimer increases.     

Silole‐core phenylacetylene dendrimers and their application in detecting picric acid

Silole‐core phenylacetylene dendrimers were designed and synthesized, among them, the model compound (n = 0) and the first generation of the dendrimer (n = 1) were obtained by the reaction of 2,5‐dibromosilole with corresponding terminal alkynes, the second generation of the dendrimers (n = 2) was synthesized from 2,5‐diiodosilole. These compounds indicated the absorptions of both phenylacetylene dendrons (250–350 nm) and silole core (400–500 nm). The first generation displayed efficient energy transfer from phenylacetylene dendrons to silole core, whose energy transfer efficiency was as high as 80%. These compounds were used as chemical sensors to probe explosive, for picric acid (PA), the Stern–Volmer constants of model compound and the first generation are 7120 and 5490M^?1, respectively. J. Heterocyclic Chem., (2012).     

Chemistry at boron: synthesis and properties of red to near-IR fluorescent dyes based on boron-substituted diisoindolomethene frameworks

A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure-fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650-800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13,000 cm(-1) depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications.     

Synthesis and photochemical characterization of a zinc phthalocyanine-zinc porphyrin heterotrimer and heterononamer

The synthesis of two phthalocyanine-porphyrin covalently linked heteromolecules are described. Intramolecular energy transfer is investigated and quantified in terms of the quantum yield of energy transfer and found to be highly effective in both molecules. The photophysical properties of both molecules are modified greatly by the presence of the porphyrin moieties on the phthalocyanine core.     

Molecular Packing and Solid-State Photophysical Properties of 1,3,6,8-Tetraalkylpyrenes

The relationship between the photophysical properties and molecular orientation of 1,3,6,8-tetraalkylpyrenes in the solid state is described herein. The introduction of alkyl groups with different chain structures (in terms of length and branching) did not affect the photophysical properties in solution, but significantly shifted the emission wavelengths and fluorescence quantum yields in the solid state for some samples. Pyrenes bearing ethyl, isobutyl, or neopentyl groups at the 1-, 3-, 6-, and 8-positions showed similar emission profiles in both the solution and solid states. In contrast, pyrenes bearing other alkyl groups exhibited an excimer emission in the solid state, similar to that of the parent pyrene. On studying the photophysical properties in the solid state with respect to the obtained crystal structures, the observed solid-state photophysical properties were found to depend on the relative position of the pyrene chromophores. The solid-state photophysical properties can be controlled by the alkyl groups, which provide changing crystal packing. Among the pyrenes tested, 1,3,6,8-tetraethylpyrene showed the highest fluorescence quantum yield of 0.88 in the solid state.     

Rainbow Perylene Monoimides: Easy Control of Optical Properties

Perylene dyes have been widely used as photoreceptors in organic photovoltaics because of their outstanding photo‐, thermal and chemical stability as well as their excellent photophysical properties. Herein we describe a novel generation of perylene dyes based on N‐(2,6‐diisopropylphenyl)‐perylene‐3,4‐dicarboximide. The optical properties of these novel perylenes can be finely tuned via the substituents in the 1‐, 6‐ and 9‐positions of the perylene core. The facile synthesis, tunable orbital and absorption properties, and electrochemical potentials help us to design efficient perylene sensitizers for solar‐cell applications.     

Conversion of intramolecular singlet electron transfer at room temperature into triplet energy transfer at 77 K: photoisomerization in norbornadiene- and carbazole-labeled poly(aryl ether) dendrimers

A series of Fréchet-type poly(aryl ether) dendrimers (CZ-Gn-NBD, n = 1-3) with carbazole (CZ) chromophores and a norbornadiene (NBD) group attached to the periphery and the core, respectively, were synthesized, and their photophysical and photochemical properties were investigated. Selective excitation of the carbazole units in CZ-Gn-NBD resulted in a singlet electron transfer from CZ to NBD at room temperature, and an intersystem crossing followed a triplet-triplet energy transfer from CZ to NBD in glassy 2-methyltetrahydrofuran at 77 K. Both singlet electron transfer and triplet energy transfer processes lead to the isomerization of the norbornadiene group into the quadricyclane (CZ-Gn-QC). The efficiencies and the rate constants for singlet electron transfer are approximately 88, 80, and 74% and 1.8 x 10(9), 6.1 x 10(8), and 4.0 x 10(8) s(-1) for generations 1-3, respectively. The quantum yields of the intramolecular photosensitized isomerization are measured to be approximately 0.013, 0.012, and 0.011, and the efficiencies of triplet norbornadiene formation via singlet electron transfer are approximately 0.070, 0.065, and 0.059 for generations 1-3, respectively. The light-harvesting ability of CZ-Gn-NBD increases with the generation due to an increase of the number of peripheral chromophores. In glassy 2-methyltetrahydrofuran at 77 K, the triplet-triplet energy transfer proceeds with efficiencies of approximately 0.86, 0.64, and 0.36 and rate constants of 0.96, 0.25, and 0.08 s(-1) for generations 1-3, respectively. The intramolecular singlet electron transfer and triplet energy transfer in CZ-Gn-NBD proceed mainly via a through-space mechanism involving the proximate donor (folding back conformation) and acceptor groups.     

Twisted, Z-shaped perylene bisimide

The first derivative of a new class of perylene bisimide chromophores, N,N'-bis(octyl)-3,9-bis(phenyl)perylene-1,2,7,8-tetracarboxyl bisimide, 1, has been synthesized and its fundamental photophysical and electrochemical properties assessed. The extended, Z-shaped structure was achieved by use of the classic photoenolization of an o-methylbenzophenone analogue, 1,5-dibenzoyl-9,10-dihydroanthracene, and in situ Diels-Alder trapping of the resulting o-xylylenol intermediates with N-octylmaleimide. Subsequent dehydration and aromatization of the resulting bisadduct afforded 1. In dichloromethane, bisimide 1 has an absorption lambdamax at 491 nm (epsilon = 29,600 M-1 cm-1), a fluorescence lambdamax at 517 nm with a high quantum yield (Phi = 0.70), and a single-exponential fluorescence decay (tau = 5.01 ns). Pure crystals of 1 have red emission, suggesting exciplex formation in the solid state. X-ray crystallographic analysis of 1 revealed significant twisting of its perylene core.     

Synthesis and physical properties of triptycene-based oligo(p-phenyleneethynylene)s

A series of symmetrical and unsymmetrical triptycene-based oligo(op-phenyleneethynylene)s were synthesized by deprotection of the acetone protected terminal alkynes, followed by Sonogashira coupling reactions. The photophysical properties of triptycene-based OPEs both in solution and solid state have been investigated by UV–Vis and fluorescence spectroscopy. Interestingly, the obtained compounds show strong fluorescence with partly high quantum yields in solid state, which suggested that triptycene moieties have not only prevented the intermolecular aggregation but also enforced the coplanarity of OPEs backbone in the solid state.