Donor-acceptor Molecules Research Articles

Efficient non-doped deep blue organic light emitting diodes with high external quantum efficiency and a low efficiency roll-off based on donor-acceptor molecules

Two phenanthroimidazole derivatives containing triphenylamine, carbazole and pyrene units were designed and synthesized. Highly efficient non-doped deep blue organic light emitting diodes (OLEDs) were fabricated by using these materials as emissive layer. The non-doped devices demonstrated high efficiency (4.24 cd/A, 3.67 lm/W, 4.66%), low efficiency roll-off at higher current densities, and stable deep blue emissions with CIEy around 0.10, which are excellent results for deep-blue OLED devices. This study reveals that the combination of phenanthroimidazole and donor-linker-acceptor strategy has a great potential for developing high performance deep-blue OLEDs.

Zero Quantum Coherence in a Series of Covalent Spin-Correlated Radical Pairs

Photoinitiated subnanosecond electron transfer within covalently linked electron donor-acceptor molecules can result in the formation of a spin-correlated radical pair (SCRP) with a well-defined initial singlet spin configuration. Subsequent coherent mixing between the SCRP singlet and triplet ms = 0 spin states, the so-called zero quantum coherence (ZQC), is of potential interest in quantum information processing applications because the ZQC can be probed using pulse electron paramagnetic resonance (pulse-EPR) techniques. Here, pulse-EPR spectroscopy is utilized to examine the ZQC oscillation frequencies and ZQC dephasing in three structurally well-defined D-A systems. While transitions between the singlet and triplet ms = 0 spin states are formally forbidden (Δms = 0), they can be addressed using specific microwave pulse turning angles to map information from the ZQC onto observable single quantum coherences. In addition, by using structural variations to tune the singlet-triplet energy gap, the ZQC frequencies determined for this series of molecules indicate a stronger dependence on the electronic g-factor than on electron-nuclear hyperfine interactions.

Blue Non-Doped Organic Light Emitting Diodes Based on a Novel Donor–Acceptor Molecule

Blue Non-Doped Organic Light Emitting Diodes Based on a Novel Donor–Acceptor Molecule

Donor–Acceptor Molecular Triangles

The synthesis and optoelectronic properties of five donor–acceptor molecules, featuring an electron-acceptor unit made of six fused benzenoid rings that resembles an equilateral triangle, are described. These molecular ‘triangles’ were synthesized in eight steps from simple building blocks such that the electron-donor substituents could be installed in the last step by means of the Suzuki cross-coupling reaction. All molecules absorb and emit visible light in the region of around 450–650 and 550–850 nm, respectively, exhibit solvatochromism, and possess up to four redox states.

E/Z isomerization, solvatachromism and aggregation-induced emission enhancement of donor-acceptor type oligo(p-phenylene vinylene)s.

A donor-acceptor molecule, PICNDSB, with cyclopenta[b]indole as the donor and (1,4-phenylene)bis(3-phenylacrylonitrile) as the acceptor, is designed and synthesized. PICNDSB shows typical aggregation-induced emission characteristics. The photoluminescence quantum yield of PICNDSB in dilute THF was only 0.7% and reaches 51.4% in the solid state. Compared with its analogue CzCNDSB, PICNDSB possesses stronger intramolecular charge transfer properties, as revealed from CV measurements, theoretical calculations, and their fluorescence behaviors. Correspondingly, the relatively more efficient electron-donating terminal group of cyclopenta[b]indole endows the molecule with a much higher two-photon absorption cross section of 1286 GM compared to CzCNDSB (357 GM).

Triphenylethylenyl-based donor–acceptor–donor molecules: studies on structural and optical properties and AIE properties for cyanide detection

Triphenylethylenyl-based donor–acceptor–donor molecules are synthesized and they exhibit a strong response to cyanide ions.

Effects of the acceptor pattern and substitution position on the properties of N-phenyl-carbazolyl based donor–acceptor–donor molecules

Four D–A–D type molecules were designed and synthesized, and their specific properties including optical, redox and thermal stabilities were studied in detail. The influence of substitution and the heteroatom effects were also studied.

2,6-Di(thiophenyl)-1,5-dihydrodipyrrolopyrazine (DT-DPP) structural isomers as donor–acceptor–donor molecules and their optoelectronic investigation

We report the synthesis and characterization of two new D–A–D molecules via Pd catalyzed C–C and C–N coupling reactions. This illustrates the potential of DT-DPP for promising optoelectronic applications.

The contributions of molecular vibrations and higher triplet levels to the intersystem crossing mechanism in metal-free organic emitters

Dual luminescence (RTP and TADF) is observed in a series of donor–acceptor–donor molecules.

Star-shaped fluorene–BODIPY oligomers: versatile donor–acceptor systems for luminescent solar concentrators

Energy transfer in star-shaped donor–acceptor molecules reduces self-absorption in luminescent solar concentrators.

Photoinduced electron transfer reaction in mitochondria for spatiotemporal selective photo-oxidation of lipids by donor/acceptor linked molecules.

Donor-acceptor-linked molecules have been synthesized and utilized to induce the rapid and site-selective lipid-oxidation in mitochondria by utilizing a photoinduced intermolecular electron transfer reaction. Two water-soluble donor-acceptor molecules (1 and 2) were designed and synthesized for this purpose. 2 was prepared to modulate its affinity to cell membrane in mitochondria. Confocal laser microscopy experiments revealed that 1 and 2 possess high localization abilities in mitochondria. By the photoinduced electron transfer, 2 exhibited the remarkable oxidation ability of lipids, mainly cardiolipin. In HeLa cells, 2 triggered mitochondrial lipid oxidation, which was followed by apoptotic cell death, under illumination within a few seconds. These results show that the present molecular system is highly promising to utilize the photoinduced intermolecular electron transfer reaction in a precise spatiotemporal manner in a cell by using light.

Experimental and Theoretical Studies of the Spectroscopic Properties of Chalcone Derivatives.

Newly synthesized, differently substituted chalcones (1,3-diaryl-2-propen-1-ones) have been studied using steady-state and time-resolved techniques combined with quantum-chemical modelling. To explore spectroscopic structure - property relationships the substituent (acceptor moiety) was chosen according to systematic variation in the Hammett parameter. It was shown that photophysical properties of the studied donor-acceptor (D-A) molecules can be predicted in terms of a simple model from the properties of individual chromophores (composite-model of decoupled moieties: donor (D) and acceptor (A)). The results of spectroscopic measurements also indicate that for investigated D-A fluorophores in medium-polar solvent, the initially populated, locally excited (LE) state (where the fundamental role plays donor moiety (D*-A)) reacts further to produce intramolecular charge transfer (ICT) state. Additionally, the experimental absorption (M ge ) and fluorescence (M eg ) transition dipole moments were calculated on the basis of spectroscopic data and compared with results of our quantum-chemical calculations. The absorption transition dipole moment was found to vary linearly with the Hammett substituent coefficient (σ).

Theoretical Investigation on Porphyrin-Based Small Molecules as Donor Materials for Photovoltaic Applications

An effective strategy to improve the efficiency of organic solar cells (OSCs) is to incorporate the porphyrin derivatives as electron-rich units into the acceptor–donor–acceptor molecules. To achieve this goal, starting from the parent molecules DTS(PTTh2)2 and DTS(FBTTh2)2 which are based on a dithieno(3,2-b;2′,3′-d)silole (DTS) electron-rich unit connected to each of two electron-withdrawing units ([1,2,5]thiadiazolo[3,4-c]pyridine (PT) and 5-fluorobenzo[c][1,2,5]thiadiazole (FBT)), we designed two types of porphyrin-based small molecules by replacing DTS unit with the porphyrin derivatives in DTS(PTTh2)2 and DTS(FBTTh2)2, respectively. From the calculated results, the porphyrin-based molecules in OSC applications not only yield an enhanced light absorptions with a redshift and stronger spectra and increased hole mobility, which is conducive to enhance the short circuit current and fill factor, but also exhibit smaller exciton binding energy and better electron transfer properties at donor/acceptor (D/A...

Optimum conjugation length in donor–acceptor molecules for third-order nonlinear optics

We report on the third-order nonlinear optical properties of a series of molecules, first published in Chem. Eur. J.19, 12693–12704 (2013)CHRYAQ0009-305X10.1002/chem.201301642, where a donor and an acceptor group are separated by a linear conjugated system consisting of only carbon atoms building triple bonds (0 to 5 acetylene spacers). We determine how the wavelength-dependent complex third-order polarizabilities of these molecules vary with the number of acetylene spacers between donor and acceptor groups. We find that both peak two-photon absorption cross sections and off-resonant third-order polarizabilities reach a maximum for 3 spacers and that their corresponding intrinsic values decrease for longer conjugation lengths. At the same time, the observed third-order polarizabilities are two orders of magnitude larger than those seen in similar molecules of similar size but without donor–acceptor substitution. There is also a resonant enhancement of the real part of the third-order polarizability that only appears for the longer molecules, and reaches ∼5 times the off-resonant value for a molecule with 4 spacers. This enhancement is found at the long-wavelength side of the two-photon absorption where the ratio between real and imaginary parts of the third-order polarizabilities still exceeds 10.

Aggregation-induced delayed fluorescence from phenothiazine-containing donor–acceptor molecules for high-efficiency non-doped organic light-emitting diodes

Highly luminescent donor–acceptor molecules based on a phenothiazine donor unit coupled with a xanthone or benzophenone acceptor unit were developed for use in organic light-emitting diodes (OLEDs). While both molecules are almost non-luminescent in pure tetrahydrofuran (THF) solution, a strong yellow delayed fluorescence was observed upon their aggregation in THF/water mixtures or in neat films. This result demonstrates the unique aggregation-induced delayed fluorescence (AIDF) characteristics of these molecules. OLEDs using these AIDF materials as a non-doped emission layer achieved high external electroluminescence quantum efficiencies of up to 11%, which exceeds the theoretical maximum for conventional fluorescent OLEDs. Highly luminescent donor–acceptor molecules based on a phenothiazine donor unit coupled with a xanthone or benzophenone acceptor unit were developed. While both molecules are almost non-luminescent in pure tetrahydrofuran (THF) solution, a strong yellow delayed fluorescence was observed upon their aggregation in THF/water mixtures and in neat films. This result demonstrates the unique aggregation-induced delayed fluorescence (AIDF) characteristics of these molecules. Organic light-emitting diodes (OLEDs) using these AIDF materials as a non-doped emission layer achieved high external electroluminescence quantum efficiencies of up to 11%, which far exceeds the theoretical maximum for conventional fluorescent OLEDs.

Molecular Engineering of Mechanochromic Materials by Programmed C-H Arylation: Making a Counterpoint in the Chromism Trend.

The development of facile methods for screening organic functional molecules through C-H bond activation is a revolutionary trend in materials research. The prediction of mechanochromism as well as mechanochromic trends of luminogens is an appealing yet challenging puzzle. Here, we present a strategy for the design of mechanochromic luminogens based on the dipole moment of donor-acceptor molecules. For this purpose, a highly efficient route to 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidines (2,7-diaryl-TAPs) has been established through programmed C-H arylation, which unlocks a great opportunity to rapidly assemble a library of fluorophores for the discovery of mechanochromic regularity. Molecular dipole moment can be employed to explain and further predict the mechanochromic trends. The 2,7-diaryl-TAPs with electron-donating groups on the 2-aryl and electron-withdrawing groups on the 7-aryl possess a relatively small dipole moment and exhibit a red-shifted mechanochromism. When the two aryls are interchanged, the resulting luminogens have a relatively large dipole moment and display a blue-shifted mechanochromism. Seven pairs of isomers with opposite mechanochromic trends are presented as illustrative examples. The aryl-interchanged congeners with a bidirectional emission shift are structurally similar, which provides an avenue for understanding in-depth the mechanochromic mechanism.

Synthesis, optical and redox properties of donor-acceptor molecules based on diketopyrrolopyrrole

A series of new donor-acceptor (D-A) functionalized diketopyrrolopyrrole (DPP) derivatives bearing different electron-donating and electron-withdrawing substituents at the terminal thiophene units were synthesized by palladium-catalyzed cross-coupling reactions. The introduction of different substituent groups can influence the properties of these DPP dyes. The optical and electrochemical properties of these synthesized DPP dyes ( DPP1 – DPP4 ) were investigated by UV-Vis and steady-state fluorescence spectroscopy and cyclic voltammetry (CV). They have 1.61–2.28 eV of band gaps and appropriate energy levels, the bistriphenyl amine (TPA) substituted DPP2 shows a strong absorption band reaching in the near-infrared (NIR) region, which is a highly desirable feature for application in organic photovoltaics.

Novel Design of Carbazole-Based Donor–Acceptor Molecules for Fullerene-Free Organic Photovoltaic Devices

Novel Design of Carbazole-Based Donor–Acceptor Molecules for Fullerene-Free Organic Photovoltaic Devices

Structure Direction, Solvent Effects, and Anion Influences in Halogen-Bonded Adducts of 2,6-Bis(iodoethynyl)pyridine

A new divergent and self-complementary halogen bond donor–acceptor molecule 2,6-bis(iodoethynyl)pyridine L has been prepared and structurally characterized, and used to generate a series of extended halogen-bonded adducts with tetrabutylammonium halide salts. The reaction between L and anions such as either bromide or chloride gives the one-dimensional polymeric species {L·TBABr} or {L·TBACl}, respectively, which contains helical strands linked by C–I···X– halogen bonds which partially encapsulate the associated organic cations. Varying the reaction solvent from ethyl acetate to 5:95 methanol/ethyl acetate gives rise to another polymeric phase on combining L with tetrabutylammonium chloride, the one-dimensional looped chain structure {L2·TBACl} in which each chloride ion acts as a four-connected square planar node for halogen bonding interactions originating from L. Similar solvent effects are observed in the discrete macrocyclic species {L·TBAI}-α and {L·TBAI}-β, both consisting of cyclic (L2I2)2– specie...

FRET Sensor for Erythrosine Dye Based on Organic Nanoparticles: Application to Analysis of Food Stuff.

An aqueous suspension of fluorescent nanoparticles (PHNNPs) of naphthol based fluorescent organic compound 1-[(Z)-(2-phenylhydrazinylidene) methyl] naphthalene -2-ol (PHN) were prepared using reprecipitation method shows bathochromically shifted aggregation induced enhanced emission (AIEE) in the spectral region where erythrosine (ETS) food dye absorbs strongly. The average size of 72.6nm of aqueous suspension of PHNNPs obtained by Dynamic light scattering results shows a narrow particle size distribution. The negative zeta potential of nano probe (-22.6mV) responsible to adsorb oppositely charged analyte on its surface and further permit to bind nano probe and analyte within the close distance proximity required for efficient fluorescence resonance energy transfer (FRET) to take place from donor (PHNNPs) to acceptor (ETS). Systematic FRET experiments performed by measuring fluorescence quenching of PHNNPs with successive addition of ETS solution exploited the use of the PHNNPs as a novel nano probe for the detection of ETS in aqueous solution with extremely lower limit of detection equal to 3.6nM (3.1ng/mL). The estimation of photo kinetic and thermodynamic parameters such as quenching rate constant, enthalpy change (∆H), Gibbs free energy change (∆G) and entropy change (∆S) was obtained by the quenching results obtained at different constant temperatures which were found to fit the well-known Stern-Volmer relation. The mechanism of binding and fluorescence quenching of PHNNPs by ETS food dye is proposed on the basis of results obtained in photophysical studies, thermodynamic parameter, energy transfer efficiency, critical energy transfer distance (R0) and distance of approach between donor-acceptor molecules (r). The proposed FRET method based on fluorescence quenching of PHNNPs was successfully applied to develop an analytical method for estimation of ETS from food stuffs without interference of other complex ingredients. Graphical Abstract A fluorescent organic nanoprobe developed for the detection of erythrosine (ETS) food dye in aqueous medium based on fluorescence resonance energy transfer (FRET). The FRET process between donor (nanoparticles) and acceptor (ETS dye) arises due to oppositely charge attraction through hydrophobic interactions. The proposed method was successfully applied to quantitative determination of ETS dye in food stuff sample collected from local market.