Photophysical properties of oligo(2,3-thienyleneethynylene)s

Photophysical properties of oligo(2,3-thienyleneethynylene)s (nTE, n denotes the number of thiophene rings, n = 2, 3) in benzene were investigated using steady-state, time-resolved fluorescence, and transient absorption spectroscopies. For 2TE, generation of the radiative S2 and nonradiative S1 states was confirmed. Upon excitation, the S2 state was initially generated and deactivated to the S1 state within 10 ps. The S1 state exhibited the transient absorption band at 470 nm, of which the lifetime was estimated to be 5.3 ns. In the case of 3TE, on the other hand, it was revealed that the radiative S1 state with a transient absorption peak at 650 nm was generated upon excitation. The T1 states of nTE were generated from the S1 states. The quantum yields were estimated to be 0.52 and 0.54 for 2TE and 3TE, respectively. Extremely fast reactions in the higher triplet excited state were indicated for both 2TE and 3TE.     

芳炔类共轭大环化合物

芳炔类大环化合物是最近10年来新兴的一种富碳共轭大环状分子，迅速发展到 近100种，可在光、电、磁、纳米等功能材料中得到广泛应用，引起了人们极大的 兴趣，对芳炔类大环化合物的研究，特别是合成方法和性质进行了综述，并提出了 这一领域的发展方向和需要解决的重点课题。     

Optical properties and delocalization of excess negative charges on oligo(phenylenevinylene)s: a quantum chemical study

A quantum chemical study of the electronic structure of negatively charged phenylenevinylene (PV) oligomers and methoxy-substituted derivatives is presented. The geometries of the PV oligomers were optimized using density functional theory. The geometry deformations are found to be delocalized along the entire oligomer chain without indication of polaron formation. The optical absorption spectra of the negatively charged PVs were calculated using both time-dependent density functional theory (TDDFT) and the singly excited configuration interaction method with an intermediate neglect of differential overlap reference wave function (INDO/s-CIS). The available experimental optical absorption energies are reproduced by the calculations. Introduction of methoxy substituents reduces the transition energies, while this does not have a strong effect on the charge distribution along the chain. DFT calculations yield a more delocalized excess negative charge than that of INDO/s-CIS calculations.     

First synthesis and electronic properties of cyano(oligo)phenothiazines

(Oligo)phenothiazinyl nitriles were synthesized in good to very good yields from bromo (oligo)phenothiazines via the Beller cyanation protocol either under conductive or under dielectric heating using NMP as a solvent. Their electronic properties were determined by absorption and emission spectroscopy and cyclic voltammetry. Cyano(oligo)phenothiazines display large Stokes-shifts (5800-8300 cm⁻¹) and substantial quantum yields (11-27%). Their reversible oxidation potentials are considerably shifted anodically due to the electron-withdrawing character of the cyano group.     

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.     

A reiterative approach to 2,3-disubstituted naphthalenes and anthracenes

[reaction: see text] Simple bis(bromoethynyl)arenediynes are easily prepared by the desilylative halogenation of the corresponding trimethylsilyl derivatives. Cycloaromatization of these halogenated enediynes leads to the otherwise difficult to prepare 2,3-dibromoarenes in good yield. Alkynylation of the resulting haloaromatic compound regenerates the soluble enediyne system, homologated by one aromatic ring. This iterative methodology can be terminated by the cycloaromatization of the unsubstituted enediyne, providing the simple acene hydrocarbon.     

Synthesis and functional properties of end-dendronized oligo(9,9-diphenyl)fluorenes

[structure: see text] A facile approach for the synthesis of a family of dendrimers OFn-EG with hole-transporting ability moieties by copper-catalyzed Buchwald's double-amination as a key reaction has been developed. These novel dendrimers exhibit good energy transfer efficiencies and very high thermal and electrochemical stabilities and have potential applications as hole transfer and emitting layers in the field of organic emitting diodes (OLEDs) or as host materials for electrophosphorescent applications.     

Photopolymerization kinetics of oligo(ethylene oxide) and oligo(methylene) oxide dimethacrylates

The influence of temperature on the photopolymerization kinetics of oligo(methylene) oxide and oligo(ethylene oxide) dimethacrylate series has been investigated by isothermal DSC. The DSC curves showed a rapid rise in rate due to the Trommsdorff effect, and then a slow decline. A shoulder, apparent on many of the DSC curves at low conversions, became more prominent when the cure temperature was lowered. The kinetics were relatively insensitive to the dimethacrylate structure in the early stages of the reaction, but became more dependent as the reaction proceeded. A previously derived mathematical model, which allows for the influence of diffusion on the rate constants, was used to predict the kinetics. The dependence of the maximum rate and conversion on the curing temperature were adequately described by the model. The experimentally observed shoulder on the rate curve was also predicated as was the evolution of the rate/time curves with curing temperature. Similar predictions were found when a nonsteady state version of the model was used. The radiation intensity exponent varied from 0.3 to 0.6 possibly due to chain-length effects and pseudo-first order termination, respectively. The final degree of conversion increased with curing temperature (T_cure) and was correlated with the flexibility of the dimethacrylate. These data were fitted to a theoretical expression relating the final conversion to the resin T_g and to the T_cure. © 1993 John Wiley & Sons, Inc.     

Thermoresponsive oligo(ethylene glycol) methacrylate colloids with antifouling surface properties

Thermoresponsive polymeric colloids attract great attention in several biotechnological applications owing to their ability to manipulate drug release characteristics in a controlled manner. Majority of these applications utilized N‐isopropylacrylamide (NIPAM)‐based particles for controlled drug release. Despite its advantages, such as easy chemical modification and well‐documented literature, a potentially important bottleneck for NIPAM in biological applications is its tendency for nonspecific protein adsorption. Herein, we report a simple way to prepare novel thermoresponsive colloids composed of oligo(ethylene glycol) side chains via precipitation polymerization technique. In addition to displaying highly reversible thermal response, these particles also have considerably low nonspecific protein adsorption when compared with NIPAM counterparts. These crosslinked poly(ethylene glycol) ethyl ether methacrylate particles were characterized using dynamic light scattering and transmission electron microscopy. The effects of co‐monomer, crosslinker and initiator on particle characteristics were investigated. Finally, particle toxicity studies were carried out using 3T3 fibroblast cell lines in MTT cytotoxicity assay. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Delineating poly(aniline) redox chemistry by using tailored oligo(aryleneamine)s: towards oligo(aniline)-based organic semiconductors with tunable optoelectronic properties

The simple and elegant Buchwald-Hartwig cross-coupling reaction has been used to synthesise a designed range of new aniline-based tetramers in one step, and without the need for protecting groups. Variation of the central aromatic ring has provided the opportunity to carefully tune the optoelectronic properties in this series, thus enabling a structure-activity relationship study by using a range of photophysical and electrochemical techniques. As a result, the long-proposed sequences of electron-electron (EE) and electron-chemical (EC) processes that support the complex redox and proton-transfer reactions involved in the well-known switching of redox states of poly- and oligo(aniline)s are revealed here for the first time. We also present the initial results from time-dependent DFT calculations to clarify the optoelectronic behaviour of these oligomers. The dc-conductivity measurements of conducting thin films of this series, doped with the prototypical poly(aniline) protonating agent D,L-camphor-10-sulfonic acid (CSA), externally plasticised with triphenyl phosphate (TPP), and processed from m-cresol (MC) solutions, are also presented.     

Backbone-rigidified oligo(m-phenylene ethynylenes)

Oligo(m-phenylene ethynylenes) (oligo(m-PE)) with backbones rigidified by intramolecular hydrogen bonds were found to fold into well-defined conformations. The localized intramolecular hydrogen bond involves a donor and an acceptor from two adjacent benzene rings, respectively, which enforces globally folded conformations on these oligomers. Oligomers with two to seven residues have been synthesized and characterized. The persistence of the intramolecular hydrogen bonds and the corresponding curved conformations were established by ab initio and molecular mechanics calculations, 1D and 2D (1)H NMR spectroscopy, and UV spectroscopy. Pentamer 5, hexamer 6, and heptamer 7 adopt well-defined helical conformations. Such a backbone-based conformational programming should lead to molecules whose conformations are resilient toward structural variation of the side groups. These m-PE oligomers have provided a new approach for achieving folded unnatural oligomers under conditions that are otherwise unfavorable for previously described, solvent-driven folding of m-PE foldamers. Stably folded structures based on the design principle described here can be developed and may find important applications.     

Emission energies and photophysical properties of ladder oligo(p-aniline)s

Emission properties and the photophysics of three ladder oligo(p-aniline)s; namely 5,11-diethyl-6,12-dimethylindolo[3,2-b]carbazole (DIMER 2P), 14-ethyl-5,8-dihydro-diindolo[3,2-b:2′,3′-h]carbazole (TRIMER 2P), and 5,8,14-triethyl-diindolo[3,2-b:2′,3′-h]carbazole (TRIMER 3P) are presented. The optimization (relaxation) of the first singlet excited electronic state (S₁) has been done using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S₁ state does not cause important changes in the geometrical parameters of the compounds, as is experimentally corroborated by the small Stokes shifts. Emission energies from the relaxed excited states have been obtained from TDDFT calculations performed on the S₁ optimized geometries and have been correlated with the corresponding fluorescence spectra of the derivatives dissolved in dichloromethane. A good agreement has been found between TDDFT emission energies and the (0,0) fluorescence bands. As predicted from theoretical calculations, all compounds exhibit small Stokes shift, which testify the rigidity of these ladder compounds. Moreover, this theoretical approach provides a good evaluation of the bathochromic shifts caused by the increase in the conjugation length or by the presence of alkyl chains on the nitrogen atoms. Finally, the fluorescence quantum yield and lifetime of the compounds in dichloromethane have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S₁ state have been determined.     

Synthesis, self-assembly, and photophysical properties of cationic oligo(p-phenyleneethynylene)s

Three series of cationic oligo p-phenyleneethynylenes (OPEs) have been synthesized to study their structure-property relationships and gain insights into the transition from molecular to macromolecular properties. The absorbance maxima and molar extinction coefficients in all three sets increase with increasing number of repeat units; however, the increase in λ(max) between the oligomers having 2 and 3 repeat units is very small, and the oligomer having 3 repeat units shows virtually the same spectra as a p-phenyleneethynylene polymer having 49 repeat units. A computational study of the oligomers using density functional theory calculations indicates that while the simplest oligomers (OPE-1) are fully conjugated, the larger oligomers are nonplanar and the limiting "segment chromophore" may be confined to a near-planar segment extending over three or four phenyl rings. Several of the OPEs self-assemble on anionic "scaffolds", with pronounced changes in absorption and fluorescence. Both experimental and computational results suggest that the planarization of discrete conjugated segments along the phenylene-ethynylene backbone is predominantly responsible for the photophysical characteristics of the assemblies formed from the larger oligomers. The striking differences in fluorescence between methanol and water are attributed to reversible nucleophilic attack of structured interfacial water on the excited singlet state.     

Synthesis and electronic properties of (oligo)phenothiazine-ethynyl-hydro-C60 dyads

Ethynyl bridged (oligo)phenothiazine-C₆₀ dyads 2 can be readily synthesized by addition of the corresponding (oligo)phenothiazinyl lithium acetylides 1 to C₆₀ followed by protonation with acetic acid. Cyclovoltammetric data of 1 and 2 reveal that the (oligo)phenothiazinyl moieties (donor) and the fullerene fragment (acceptor) are electronically decoupled in ground state, yet, each additional phenothiazine lowers the HOMO-LUMO gap by 100 mV. Upon UV excitation the phenothiazinyl fluorescence is considerably quenched, presumably as a consequence of a charge separation by an intramolecular photo-induced electron transfer from phenothiazine to fullerene.     

Synthesis of fullerene-substituted oligo(phenylenebutadiyndiyl)

A diethynylbenzene monomer substituted with two fullerene moieties has been prepared, and its oligomerization performed in the presence of phenylacetylene as end-capping reagent afforded the corresponding end-capped mono- and di-mer with an oligo(phenylenebutadiyndiyl) (OPB) conjugated backbone substituted with two and four fullerene subunits, respectively.     

First syntheses and electronic properties of (oligo)phenothiazine-C60 dyads

(Oligo)phenothiazine-C₆₀ dyads 3 can be readily synthesized by a three-component condensation-cycloaddition of the corresponding (oligo)phenothiazinyl carbaldehydes 1, N-hexyl glycine (2), and C₆₀. Cyclic voltammetry of 3 and reference compounds 4 shows that the phenothiazinyl moiety (donor) and the fullerene fragment (acceptor) are electronically decoupled in ground state. However, upon UV excitation the phenothiazinyl fluorescence is considerably quenched, presumably as a consequence of a charge separation by an intramolecular photo-induced electron transfer from phenothiazine to fullerene.     

Heteroaromatic alanine derivatives bearing (oligo)thiophene units: synthesis and photophysical properties

A series of new benzoxazolylalanine derivatives bearing (oligo)thiophene units at the side chain were synthesized in good yields. The photophysical characterization of these amino acids was performed by UV-vis absorption and fluorescence emission studies and revealed that some of the compounds display high fluorescent quantum yields, making them good candidates for application as fluorescent probes.     

Solid-phase synthesis of oligo(p-benzamide) foldamers

[reaction: see text] A coupling protocol has been developed which allows the synthesis of oligo(p-benzamide)s on solid support. Aromatic carboxylic acids are activated in situ with thionyl chloride and used to acylate secondary aromatic amines. N-p-Methoxy benzyl (PMB) as well as N-hexyl protected monomers were investigated. Heterosequences of both monomers were synthesized. Such nanoscale objects are important building blocks for supramolecular chemistry.