Donor End Groups Research Articles

Structure-Property Relationship of Three 2-Chloro-4-fluoro Chalcone Derivatives: A Comprehensive Study on Linear and Non-linear Optical Properties, Structural Characterizations and Density Functional Theory

This work focused on the relationship between molecular structure and non-linear optical (NLO) property of the chalcone derivatives. The NLO property is well known increased by push-pull effect, therefore we have explored donor-acceptor substitutions on both rings to develop excellent NLO materials. Three new crystals of 2-chloro-4-fluorochalcone derivatives bearing various donor end groups were synthesized in order to evaluate the donor dependence of their second-order hyperpolarizability γ. The grown crystals were spectroscopically confirmed and crystallographically analysed. Their intermolecular interactions were visualized by Hirshfeld surface analysis. The electronic absorption spectrums were investigated by experimental and theoretical methods, to discuss the intramolecular charge transfer and energy gap of solution sample, which defined significantly affected NLO properties. Theoretical electronic properties have been simulated with density functional theory (DFT) at B3LYP/6-311++G (d,p) level and compared with experimental results. Thermally-induced NLO parameters such as non-linear absorption (NLA) coefficient (α2∼10−5 cmW−1), non-linear refractive (NLR) index (n2 ∼10−9cm2W−1), third-order susceptibility [χ(3)(-ω;ω,ω,-ω) ∼10−8 esu] and γ(-ω;ω,ω,-ω)∼ 10−27 esu] were measured by Z-scan technique under continuous-wave laser excitation (532 nm). The solution samples exhibit two-photon assisted reverse saturable absorption and self-defocusing non-linear refraction, optical limiting and all-optical switching behaviours. We have determined that γ depends on the strength of donor/acceptor substituents, which is the result of the two contributions: the energy gap and the transition dipole moment between the ground and first excited states. A large value of γ was found for compound I which bearing strong donor hydroxy substituent, thus the hydroxychalcone derivatives as a potential material with excellent NLO performance.

Stealth Luminescent Organic Nanoparticles Made from Quadrupolar Dyes for Two-Photon Bioimaging: Effect of End-Groups and Core.

Molecular-based Fluorescent Organic Nanoparticles (FONs) are versatile light-emitting nano-tools whose properties can be rationally addressed by bottom-up molecular engineering. A challenging property to gain control over is the interaction of the FONs’ surface with biological systems. Indeed, most types of nanoparticles tend to interact with biological membranes. To address this limitation, we recently reported on two-photon (2P) absorbing, red to near infrared (NIR) emitting quadrupolar extended dyes built from a benzothiadiazole core and diphenylamino endgroups that yield spontaneously stealth FONs. In this paper, we expand our understanding of the structure-property relationship between the dye structure and the FONs 2P absorption response, fluorescence and stealthiness by characterizing a dye-related series of FONs. We observe that increasing the strength of the donor end-groups or of the core acceptor in the quadrupolar (D-π-A-π-D) dye structure allows for the tuning of optical properties, notably red-shifting both the emission (from red to NIR) and 2P absorption spectra while inducing a decrease in their fluorescence quantum yield. Thanks to their strong 1P and 2P absorption, all FONs whose median size varies between 11 and 28 nm exhibit giant 1P (106 M−1.cm−1) and 2P (104 GM) brightness values. Interestingly, all FONs were found to be non-toxic, exhibit stealth behaviour, and show vanishing non-specific interactions with cell membranes. We postulate that the strong hydrophobic character and the rigidity of the FONs building blocks are crucial to controlling the stealth nano-bio interface.

Exciton Binding Energy of Non‐Fullerene Electron Acceptors

The past three years have witnessed the power conversion efficiency (PCE) of organic solar cells (OSCs) rocketing to over 18%, due to outstanding advantages of non‐fullerene acceptors (NFAs). However, large exciton binding energy (Eb) caused by strong Coulombic force is still one of the main limiting factors for high‐performance OSCs. Thus, it is critical to reduce theEbfor further enhancement of device performance. Many strategies have been developed to reduce theEbof organic materials previously. In this perspective, the calculation methods forEband the relationship betweenEband voltage loss (Vloss) are discussed. Then, the effects of the properties of small‐molecule acceptors onEbfrom the perspectives of fused‐ring donor cores, end groups, side chains, and molecular packing are discussed. Finally, the potential directions for reducingEband pointing out the trade‐off betweenEband bandgaps/miscibility are put forward. It is hoped that this perspective could provide a new thinking of a molecular design for the breakthrough of OSCs.

INVESTIGATION OF LOW-TEMPERATURE FLUORESCENCE AND ABSORPTION SPECTRA OF HIGHLY STABLE MERO-CYANINES DERIVATIVES OF 2, 6-DI-TERT-BUTYL-4-[R]-CYCLOHEXA-2, 5-DIENONE

This work presents the results of the investigation of the dependence of the fluorescence and absorption spectra of merocyanines, derivatives of the 2,6-di-tret-butyl-4-[R]-cyclohexa-2,5-dienone, on the nature of donor end groups (pyridinium, quinolinium, pyrilium, benzo[c,d]indolium, benzoimidindolium). Quantum-chemical calculation of the distribution was organized to electronic density and lengths of the relationships, which has shown that introduction tert-butyl groups in nucleus cyclohexa-2,5-dienone practically does not influence upon the general characteristic merocyanines in contrast with hydrogen. The stability merocyanines vastly increases when entering tert-butyl groups in cyclohexa-2,5-dienone. But such three-dementional groups vastly complicate the bands of the absorption, which become broader, have a complex oscillatory structure. So more suitable spectrums turned out to be for interpreting electronic transition to fluorescences, to measure at the temperature of the fluid nitrogen. As it is seen, spectral bands become more structuring with clearly marked by maximum of the transition. Well-defined 0`→ 0 vibronical transition was found at use of the low-temperature fluorescent spectra. Merocyanines with highly stable tert-butyl groups can be used as fluorescence probes and labels in chemistry and biology, active and passive components for tunable dye lasers, highly effective materials for non-linear optic.

Boron Difluoride Curcuminoid Fluorophores with Enhanced Two-Photon Excited Fluorescence Emission and Versatile Living-Cell Imaging Properties.

The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time-dependent (TD)-DFT calculations confirm the charge-transfer character of the second lowest-energy transition band and ascribe the lowest energy band to a "cyanine-like" transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV-visible absorption and fluorescence spectra. Two-photon-excited fluorescence and Z-scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two-photon cross section, reaching 5000 GM, with predominant two-photon absorption from the S0-S2 charge-transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two-photon active band for the curcuminoid derivatives has the same intramolecular charge-transfer character and therefore arises from a dipolar structure. Overall, this structure-relationship study allows the optimization of the two-photon brightness (i.e., 400-900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission.

Solution processed bulk heterojunction solar cells based on A–D–A small molecules with a dihydroindoloindole (DINI) central donor and different acceptor end groups

The optimized devices after TSA treatment showed PCEs of 7.04% and 6.16% when employing DIN-IND : PC71BM (1 : 2) and DIN-CN : PC71BM (1 : 2), respectively.

Extraction and Transport of Amino Acids Using Kryptofix 5 as Carrier through Liquid Membrane

The present work explores membrane‐mediated extraction and transport studies of amino acids through artificial bulk liquid membrane system with kryptofix 5 as a carrier. The various reaction parameters such as amino acid concentration, carrier concentration, time, pH, and stirring effect were studied to optimize reaction conditions. The stirring of source and receiving phases increased the efficiency of extraction process. Noncyclic receptor kryptofix 5 with five oxyethylene units and terminal aromatic donor end groups governs its transport and extraction efficiency. The extraction and transport efficiency followed the following trend: valine > alanine > glycine > threonine. Supported liquid membrane (SLM) studies were performed using cellulose nitrate, PTFE, eggshell, and onion membranes. The egg shell membrane support proved to be most efficient due to intricate network of water insoluble proteins fibers with very high surface area and homogeneity.

Synthesis and Photophysics of Fully π-Conjugated Heterobis-Functionalized Polymeric Molecular Wires via Suzuki Chain-Growth Polymerization

We present a fast and efficient in situ synthetic approach to obtain fully π-conjugated polymers with degrees of polymerization up to 23 and near quantitative (>95%) heterobis-functionalization. The synthesis relies on the key advantages of controlled Suzuki chain-growth polymerization: control over molecular weight, narrow polydispersity, and ability to define polymer end groups. The first end group is introduced through the initiator metal complex tBu(3)PPd(X)Br, while the second end group is added by quenching of the chain-growth polymerization with the desired boronic esters. In all cases, polymers obtained at 50% conversion showed excellent end group fidelity and high purity following a simple workup procedure, as determined by MALDI-TOF, GPC, and (1)H and 2D NMR. End group functionalization altered the optoelectronic properties of the bridge polymer. Building on a common fluorene backbone, and guided by DFT calculations, we introduced donor and acceptor end groups to create polymeric molecular wires exhibiting charge transfer and energy transfer as characterized by fluorescence, absorption, and transient absorption spectroscopy as well as by fluorescence lifetime measurements.

Theoretical study of two-photon absorption properties and up-conversion efficiency of new symmetric organic π-conjugated molecules for photovoltaic devices

Organic material with high intensity of two-photon absorption (TPA) induced fluorescence can be used as the frequency up-converter materials for improving efficiency of the solar cells. In this work, the organic molecular structures were designed by symmetrically grafting two elongated conjugated linkers on a conjugated core and then adding donor groups at both terminals. Fluorene derivatives as a core acceptor, phenylethynyl as the conjugated linker and diphenylamino or methyl-9H-carbozole as the donor end groups were selected. Quantum mechanical modeling techniques were applied to investigate the molecular electronic structure and properties. Absorption properties of these novel π-conjugated organic molecules were studied. The TPA cross-sections of these derivatives were calculated using few-states models, respectively. The effects of donor and acceptor groups on the TPA behaviors of these designed molecules were investigated. The up-conversion efficiency of designed molecules was also calculated.

Synthesis, Structural Characterization, and Physical Properties of Alkylammonium Derivative Complex with Acyclic Crown Ether Analog

The complexation abilities of cyclic or acyclic crown-type polyethers toward metal cations, ammonium (or alkylammonium) ion, and neutral molecules have attracted much attention during the last four decades because of their contributions to stereoselective complexation, cation transport, and enzyme chemistry. It is well-known that the cyclic polyethers such as 18-crown-6 show the excellent complexing ability and selectivity for the guest species with or without the charge. On the other hand, the complexation abilities of the acyclic polyethers are weaker because of their conformational freedom as well as much less effective complexation process. However, the complexing abilities of the dipodal type acyclic polyethers are improved remarkably when they have rigid aromatic donor end-groups at the both ends of the oligo(ethylene glycol) backbone. Among these, 1,13-bis-(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (L) is representative and has already been extensively investigated for its complexation ability toward several cationic or neutral guests because L has the attractive characteristics forming the pseudo-cyclic complexes with guest species in a manner similar to 18-crown-6. However, the crystal structures reported for complexation between L and the guest species, especially organic guests, are still rare.

OPE/OPV H-mers: synthesis, electronic properties, and spectroscopic responses to binding with transition metal ions

A new type of structurally defined H-shaped OPE/OPV co-oligomers (termed H-mers) functionalized with various donor and/or acceptor end groups was synthesized by iterative Sonogashira coupling and Horner–Wadsworth–Emmons (HWE) reactions. Electronic substitution effects on the H-mer backbone were investigated by UV–vis absorption and fluorescence spectroscopy. Some H-mers were found to show spectral responses upon binding to an acid (TFA) or transition metal ions, revealing the applicability of H-mers in the field of chromophore and fluorophore based chemosensors.

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

A combined experimental and theoretical study is conducted on a series of model compounds in order to assess the combined role of branching and charge symmetry on absorption, photoluminescence, and two-photon absorption (TPA) properties. The main issue of this study is to examine how branching of quadrupolar chomophores can lead to different consequences as compared to branching of dipolar chromophores. Hence, three structurally related pi-conjugated quadrupolar chromophores symmetrically substituted with donor end groups and one branched structure built from the assembly of three quadrupolar branches via a common donor moiety are used as model compounds. Their photophysical properties are studied using UV-vis spectroscopy, and the TPA spectra are determined through two-photon excited fluorescence experiments using femtosecond pulses in the 500-1000 nm range. Experimental studies are complemented by theoretical calculations. The applied theoretical methodology is based on time-dependent density functional theory, the Frenkel exciton model, and analysis in terms of the natural transition orbitals of relevant electronic states. Theory reveals that a symmetrical intramolecular charge transfer from the terminal donating groups to the middle of the molecule takes place in all quadrupolar chromophores upon photoexcitation. In contrast, branching via a central electron-donating triphenylamine moiety breaks the quadrupolar symmetry of the branches. Consequently, all Frank-Condon excited states have significant asymmetric multidimensional charge-transfer character upon excitation. Subsequent vibrational relaxation of the branched chromophore in the excited state leads to a localization of the excitation and fluorescence stemming from a single branch. As opposed to what was earlier observed when dipolar chromophores are branched via the same common electron-donating moiety, we find only a slight enhancement of the maximum TPA response of the branched compound with respect to an additive contribution of its quadrupolar branches. In contrast, substantial modifications of the spectral shape are observed. This is attributed to the subtle interplay of interbranch electronic coupling and asymmetry caused by branching.

Theoretical Study of One- and Two-Photon Absorption Properties of Octupolar D2d and D3 Bipyridyl Metal Complexes

The molecular equilibrium structures, electronic structures, and one- and two-photon absorption (TPA) properties of C2v (Zn(II), Fe(II) and Cu(I)) dipolar and D2d (Zn(II) and Cu(I)) and D3 (Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands have been studied by the ZINDO-SOS method. The calculated results show that one- and two-photon absorption properties of metal complexes are strongly influenced by the nature of the ligands (donor end groups and pi linkers) and metal ions as well as by the symmetry of the complexes. The length of the pi-conjugated backbone, the Lewis acidity of the metal ions, and the increase of ligand-to-metal ratio result in a substantial enhancement of the TPA cross sections of metal complexes. Substitution of C=N and N=N for C=C plays an important role in altering the maximum TPA wavelengths and the maximum TPA cross sections of metal complexes. Of them, the C=N substituted metal complexes have relatively large TPA cross sections. Replacing styryl with thienylvinyl makes the one-photon absorption wavelength red shift and at the same time leads to a great decrease of the maximum TPA cross sections of metal complexes. The possible reason is discussed. In the range 500-1250 nm, octupolar metal complexes exhibit intense TPAs and therefore are promising candidates for TPA materials.

Synthesis, Fluorescence, and Two‐Photon Absorption of a Series of Elongated Rodlike and Banana‐Shaped Quadrupolar Fluorophores: A Comprehensive Study of Structure–Property Relationships

An extensive series of push-push and pull-pull derivatives was prepared from the symmetrical functionalization of an ambivalent core with conjugated rods made from arylene-vinylene or arylene-ethynylene building blocks, bearing different acceptor or donor end-groups. Their absorption and photoluminescence, as well as their two-photon-absorption (TPA) properties in the near infrared (NIR) region, were systematically investigated to derive structure-property relationships and to lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Whatever the nature of the core or of the connectors, push-push systems were found to be more efficient than pull-pull systems, and planarization of the core (fluorene versus biphenyl) always leads to an increase in the TPA cross sections. In contrast, increasing the conjugation length as well as replacement of a phenylene moiety by a thienylene moiety in the conjugated rods did not necessarily lead to increased TPA responses. The present study also demonstrated that the topology of the conjugated rods can dramatically influence the TPA properties. This is of particular interest in terms of molecular engineering for specific applications, as both TPA properties and photoluminescence characteristics can be considerably affected. Thus, it becomes possible to optimize the transparency/TPA and fluorescence/TPA efficiency trade-offs for optical limiting in the red-NIR region (700-900 nm) and for two-photon-excited fluorescence (TPEF) microscopy applications, respectively.

2‐Arylthienyl‐Substituted 1,3‐Benzothiazoles as New Nonlinear Optical Chromophores.

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2‐Arylthienyl‐Substituted 1,3‐Benzothiazoles as New Nonlinear Optical Chromophores

AbstractA series of nonlinear optical chromophores 6 containing a substituted benzothiazole ring have been synthesized and characterized. 1,3‐Benzothiazoles 6 were prepared by treating various formyl derivatives of thienyl compounds withortho‐aminobenzenethiol in fair to excellent yields. These in turn were prepared by Suzuki coupling between aryl and thienyl precursors. The electronic interactions between donor and acceptor end groups in the conjugated 1,3‐benzothiazoles 6 are revealed by the intense and markedly solvatochromic CT transitions. The solvatochromic behaviour of compounds 6 was determined by linear regression analyses of absorption maxima in several solvents, where benzothiazole 6f was found to be a very appropriate indicator dye whose absorption wavenumbers (Δ$\tilde {\nu}$max = 1590 cm–1) in aliphatic and dipolar aprotic and in aromatic and chlorinated solvents correlated excellently with the π* values defined by Kamlet and Taft. Hyper‐Rayleigh scattering was used to measure the first hyperpolarizabilities β of the aforementioned compounds. Thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that good nonlinearity and thermal stability are well balanced for chromophores 6, making them good candidates for device applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, electronic structure, and absorption spectra of the merocyanines derived from pyranes and benzopyranes

The synthesis, peculiarities of the electron structure and spectral properties of the merocyanine derivatives of the pyranes and benzopyranes with nitrogen-containing heterocycles as donor end groups are presented. It is established that an annelation of the pyrane residue leads to bathochromic shift of the absorption band. Because of the considerable change in the dipole momentum upon excitation, the merocyanines studied show high sensitivity to the solvent polarity.

Improved Molecular Rectification from Self-Assembled Monolayers of a Sterically Hindered Dye

Self-assembled monolayers (SAMs) formed from the reaction of 1-(10-acetylsulfanyldecyl)-4-[2-(4-dimethylaminonaphthalen-1-yl)-vinyl]-quinolinium iodide (1a) and gold-coated substrates exhibit asymmetric current-voltage (I-V) characteristics with a rectification ratio of 50-150 at +/-1 V. It is the highest to date for a molecular diode, and the improved behavior may be assigned in part to the controlled alignment of the donor-(pi-bridge)-acceptor moieties and in part to steric hindrance, which imposes a nonplanar structure and effectively isolates the molecular orbitals of the donor and acceptor end groups. The molecular origin of the rectification is verified by its suppression upon exposure to HCl vapor, which protonates the dimethylamino group and inhibits the electron-donating properties, with restoration upon exposure to NH3. It is also established by a reduced rectification ratio of ca. 2 at +/-1 V when the cationic D-pi-A+ moieties adopt an antiparallel arrangement in self-assembled films of the derivative, bis-[1-(10-decyl)-4-[2-(4-dimethylaminonaphthalen-1-yl)-vinyl]-quinolinium]-disulfide diiodide (1b), which adsorbs via one of its terminal donors without rupture of the sulfur-sulfur bond: Au/D-pi-A+-C10H20-S-S-C10H20-+A-pi-D (I-)2.

Electronic properties of polymethine systems. 11. Absorption spectra and nature of electron transitions in cationic oxystyryl and their neutral derivatives

Complex quantum-chemical and spectral study of the features of the electron transitions and absorption spectra of the both oxystyryls and related merocyanines containing the pyridinium, quinolinium, indolium and benz[ c, d]indolium end residues has been performed. It was shown that the relative long wavelength absorption of the neutral merocyanines, in comparison with the cationic dyes, is caused by considerable redistribution of the electron density within the chromophore upon excitation, not by equalizing of the carbon–carbon bond lengths as it was predicted in the framework of the conception “cyanine limit”. The opposite sign change of the dipole momentum in the excited state in the cationic and neutral dyes depends noticeably on the basicity of the donor end groups and causes the opposite solvatochromism which increases additionally the distance between the absorption bands of these dyes of the different types.

Synthesis, linear, and quadratic-nonlinear optical properties of octupolar D3 and D2d bipyridyl metal complexes.

A series of D3 (Fe(II), Ru(II), Zn(II), Hg(II)) and D2d (Cu(I), Ag(I), Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands has been synthesized, and their thermal, linear (absorption and emission), and nonlinear optical (NLO) properties were determined. Their quadratic NLO susceptibilities were determined by harmonic light scattering at 1.91 microm, and the molecular hyperpolarizability (beta0) values are in the range of 200-657 x 10(-30) esu for octahedral complexes and 70-157 x 10(-30) esu for tetrahedral complexes. The octahedral zinc(II) complex 1 e, which contains a 4,4'-oligophenylenevinylene-functionalized 2,2'-bipyridine, exhibits the highest quadratic hyperpolarizability ever reported for an octupolar derivative (lambdamax=482 nm, beta1.91(1 e)=870 x 10(-30) esu, beta0(1 e)=657 x 10(-30) esu). Herein, we demonstrate that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and pi linkers), and the nature of the metallic centers. For example, the length of the pi-conjugated backbone, the Lewis acidity of the metal ion, and the increase of ligand-to-metal ratio result in a substantial enhancement of beta. The contribution of the metal-to-ligand (MLCT) transition to the molecular hyperpolarizability is also discussed with respect to octahedral d6 complexes (M=Fe, Ru).