Search

Three V-shaped host molecules with a cyclohexane linker were successfully synthesized for thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The unipolar host molecules, BBCzC and BTDC, contained two 9-phenyl-9H-3,9'-bicarbazole (PBCz) moieties and two 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (PDBNA) moieties, respectively. BCzTC, a bipolar host molecule, consisted of a donor unit, PBCz, and an acceptor unit, PDBNA, connected by a cyclohexane linker. Three host molecules showed good solubility in various organic solvents, making them suitable for solution processing. Among the solution-processed green TADF-OLEDs using three host molecules and a green TADF emitter, the one with BCzTC showed the highest external quantum efficiency of up to 30% with a high power efficiency of 71 lm W-1 and a current efficiency of 102 cd A-1. Compared with BBCzC and BTDC, BCzTC exhibited a relatively high photoluminescence quantum yield (PLQY), an excellent balance in hole and electron transport properties in the emitting layer, and more efficient energy transfer to the emitter, giving such an excellent device performance.

Two new hole transport styrene polymers, 2DMFCz and 2DBFCz, were successfully synthesized via radical polymerization. The design concept aims to investigate the hole-transporting ability and energy-level tunability by introducing bis(9,9-dimethyl-9H-fluoren-2-yl)aminocarbazole and bis(dibenzo[b,d]furan-2-yl)aminocarbazole as side-chain pendants. They were found to show good solubility in chlorobenzene but poor solubility in toluene, similar to poly(9-vinylcarbazole) (PVK). The highest occupied molecular orbital levels of 2DMFCz and 2DBFCz were determined to be −5.23 eV and −5.31 eV, respectively, while hole mobilities were estimated to be 1.65 × 10−7 cm2 V−1 s−1 and 1.48 × 10−8 cm2 V−1 s−1 measured by the space-charge limited-current method. Subsequently, in solution-processed green thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs), the 2DMFCz- and 2DBFCz-based devices exhibited a relatively low turn-on voltage of 2.7 V and higher maximum external quantum efficiencies of 23.84% and 21.11%, respectively. These values were superior to those of a PVK-based device. The polymer hole-transport materials presented in this study are promising materials that can play a significant role in improving the performance of TADF-OLEDs fabricated through a solution process in the future.

Recently, various host materials have been developed for solution-processed thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Compared with small-molecule hosts, polymeric hosts are advantageous for inducing a uniform distribution and segregation of dopant molecules in the emissive layer without undesired large-scale phase separation. In this study, new polymer hosts were demonstrated, in which a bipolar conjugative moiety consisting of a carbazole (Cz) donor and an α-carboline (α-Cb) acceptor was bound to the polystyrene backbone through a non-conjugated linker. They exhibited high triplet energies of >2.8 eV, and their emission spectra overlapped with the absorption spectrum of a green TADF emitter, which allowed facile energy transfer from the polymeric host to the small-molecule dopants. High device performance was observed, with external quantum efficiencies (EQEs) of 13.65, 17.09, and 17.48% for solution-processed green TADF-OLEDs using PSCzCz, PSCzCb, and PSCbCz, respectively, as hosts for the EML. The EQEs of bipolar host (PSCzCb and PSCbCz)-based devices were higher than those of unipolar host (poly(N-vinylcarbazole) and PSCzCz)-based devices owing to the well-balanced charge-carrier transport. According to these results, the polymeric host bearing a bipolar Cz and α-Cb coupled moiety is a promising material for solution-processable TADF-OLEDs.

The use of soluble host materials and thermally activated delayed fluorescence (TADF) emitters is indispensable for developing high-efficiency organic light-emitting diodes (OLEDs) by cost-effective solution processes. In this study, two bipolar hosts were designed as structural isomers, namely 3-(3,5-di(9H-carbazol-9-yl)phenyl)-9H-xanthen-9-one (Xp-mCP) and 2-(3,5-di(9H-carbazol-9-yl)phenyl)-9H-xanthen-9-one (Xm-mCP). The two host materials were synthesized by combining the unipolar host, 1,3-di(9H-carbazol-9-yl)benzene (mCP) with 9H-xanthen-9-one as an electron-accepting moiety. The two hosts exhibit good solubility in various organic solvents and high triplet energy (ET = 2.67 eV for Xp-mCP and ET = 2.82 eV for Xm-mCP), which renders them suitable for t4CzIPN-containing solution-processable green TADF-OLEDs. The maximum external quantum efficiency (EQE) values were 19.3% and 22.0% for Xp-mCP- and Xm-mCP-based green TADF-OLED, respectively. Among them, the device comprising Xm-mCP showed an excellent efficiency roll-off behavior by displaying only a 4.5% decrease and 11.4% decrease at 1000 cd m−2 and 2000 cd m−2, respectively. These results show the significant potential of xanthone-mCP host materials to develop solution-processable OLED technologies.

In this study, two polymeric host materials, P(NmCP) and P(mCP), were synthesized, and high-performing sky-blue and green thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs) were achieved. The simple structure polymer host was designed by inserting a pyridine group into the core of P(NmCP) and an electron-donating phenyl group into the core of P(mCP). The two polymeric hosts exhibited high triplet energies (T1 = 3.04 eV for P(NmCP) and 3.05 eV for P(mCP)), which were sufficiently high to realize blue and green TADF-OLEDs. In brief, solution-processed OLEDs with an emissive layer bearing P(NmCP) as a bipolar electron host exhibited remarkable performance with a maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 70.36 cd A−1, 63.15 lm W−1, and 20.07%, respectively, in the green-emitting device. In the blue-emitting device, we obtained a maximum CE, PE, and EQE of 27.13 cd A−1, 22.30 lm W−1, and 10.70%, respectively. The polymer design with such a high T1 value is believed to be the cornerstone for implementing high-performance TADF-OLEDs via solution processing in the future.

A new photocrosslinkable hole-transporting homopolymer (PX2Cz) was successfully synthesized using 9-((3-methyloxetan-3-yl)methyl)-9′-(4-vinylbenzyl)-9H,9′H-3,3′-bicarbazole monomer via radical polymerization. Biscarbazole, as a hole-transporting material, has two reactive sites that can introduce a radical polymerizable styrene moiety and a photocrosslinkable oxetane moiety. The photocuring temperature and time for the PX2Cz film was optimized to be 120 °C and 10 s. The photocured films showed good solvent resistance, which is favorable for the deposition of an emitting-layer solution on them. In particular, the highest occupied molecular orbital (HOMO) energy of the as-cast PX2Cz film was determined to be −5.37 eV which remained unchanged even after photocuring, thus facilitating hole transportation from the hole-injection layer. Subsequently, solution-processed, green, thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs) were manufactured using PX2Cz as the hole-transport material. The devices displayed a notable performance with an exceptionally low turn-on voltage (Von) of only 2.8 V and a high external quantum efficiency (EQE) of 22.5%; these values are substantially better than those of commonly used poly(9-vinylcarbazole) (PVK)-based OLEDs (Von = 3.6 V, EQE of 15.5%). The remarkably low turn-on voltage and high EQE were ascribed to the shallower HOMO energy level and more pronounced hole-transport ability of the photocured PX2Cz film.

In this study, we have synthesized a new asymmetric n-type semiconducting molecule (Me-ITBD) by combining 4,4-bis(4-hexylphenyl)-7-methyl-6-(thiophen-2-yl)-4H-indeno[1,2-b]thiophene with 2-(benzo[c][1,2,5]-thiadiazol-4-yl methylene)-malononitrile and applied it to polymer solar cells. Compared to the PhITBD acceptor without methyl substituent in the 7-position of the core, Me-ITBD showed a larger torsional angle between thiophene and indenothiophene. Non-fullerene polymer solar cells (PSCs) with the methyl-substituted asymmetric acceptor Me-ITBD displayed an enhanced power conversion efficiency (PCE) of 5.75%, compared to the PSC (PCE = 1.79%) based on a PhITBD acceptor. The higher PCE value of the Me-ITBD-based PSC was ascribed to its improved device parameters, i.e. the Jsc and FF, induced by a favorable fine morphology in the active layer. By simply introducing a methyl substituent in the indenothiophene unit of the PhITBD acceptor, the PSC performance was enhanced.

Organic polymers that exhibit features pertinent to functioning as host materials for thermally activated delayed fluorescence (TADF) emitters have considerable potential in solution-processable organic light-emitting diodes (OLEDs), allowing simple, low-cost, and large-area applications. In particular, polymer hosts have superior characteristics, including facile functionality to introduce various electron donor and acceptor entities, the ability to uniformly disperse and contain small molecular dopants, and the ability to produce more smooth and homogeneous films, compared to those of their small-molecule counterparts. This manuscript describes the design and development of three new styrene-based copolymers (ABP91, ABP73, and ABP55) bearing diphenylacridine as the electron donor and 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene as the electron acceptor. In particular, ABP91, ABP73, and ABP55 were synthesized via variations in the ratio of donor to acceptor monomers to substantiate their influence in OLED applications. With the ability of the styrene backbone of interrupting the direct electronic coupling between the adjacent electron donor and acceptor entities through non-conjugated linkages, high triplet energy can be inherited by the resulting polymers (>2.70 eV). Furthermore, these materials manifest thermal robustness through high decomposition temperatures (between 348 and 366 °C) and high glass transition temperatures (between 234 and 277 °C). Consequently, solution-processable OLEDs fabricated using the newly synthesized copolymers as host materials and the familiar t4CzIPN as a green-emissive TADF dopant deliver state-of-the-art performance with maximum external quantum efficiencies of 21.8, 22.2, and 19.7% for ABP91, ABP73, and ABP55, respectively. To our knowledge, this is, to date, the best performance reported when organic polymers are used as host materials in solution-processable TADF OLEDs. The pragmatic outcomes obtained in this study can provide useful insights into the structure-property relationship to the OLED community for the further development of efficient polymer hosts for use in solution-processable TADF OLEDs.

In this study, two host materials, pCzBzbCz and pCzPybCz, are synthesized to achieve a high efficiency and long lifetime of blue thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The molecular design strategy involves the introduction of a pyridine group into the core structure of pCzPybCz as an electron-withdrawing unit, and an electron-donating phenyl group into the structure of pCzBzbCz. These host materials demonstrate good thermal stability and high triplet energy (T1 =3.07 eV for pCzBzbCz and 3.06 eV for pCzPybCz) for the fabrication of blue TADF-OLEDs. In particular, pCzPybCz-based OLED devices demonstrate an external quantum efficiency (EQE) of 22.7 % and an operational lifetime of 24 h (LT90 , time to attain 90 % of initial luminance) at an initial luminance of 1000 cd m-2 . This superior lifetime could be explained by the C-N bond dissociation energy (BDE) in the host molecular structure. Furthermore, a mixed-host system using the electron-deficient 2,4-bis(dibenzo[b,d]furan-2-yl)-6-phenyl-1,3,5-triazine (DDBFT) is proposed to inhibit the formation of the anion state of our host materials. In short, the device operational lifetime is further improved by applying DDBFT. The carbazole-based asymmetric host molecule containing a pyridine core realizes a high-efficiency blue TADF-OLED showing a positive effect on the operating lifetime, and can provide useful strategies for designing new host materials.

Organic entities that can transport electrons are seldom available to develop adequate bipolar host materials applicable for solution-processable thermally activated delayed fluorescence (TADF)-organic light-emitting diodes (OLEDs). Therefore, the introduction of new electron-affine entities that plausibly demonstrate high triplet energy (ET) is of urgent need. In this contribution, we introduced benzimidazo[1,2-a][3,1]benzothiazine (BBIT) as a novel electron-affine entity and developed two new bipolar host materials, CzBBIT and 2CzBBIT. Both host materials exhibit high ET of 3.0 eV, superior thermal robustness with the thermal decomposition temperature of up to 392 °C, a glass transition temperature of up to 161 °C, and high solubility in common organic solvents. Single-carrier devices evidenced that both the hosts manifest balanced charge-carrier transport properties. Consequently, the solution-processable OLEDs fabricated using a recognized IAcTr-out as the green TADF emitter doped into CzBBIT as the host, realized a maximum external quantum efficiency (EQE) of 23.3%, while the 2CzBBIT: IAcTr-out blend film-based device displayed an EQE of 18.7%. These outcomes corroborated that this work could shed light on the scientific community on the design of new electron-affine entities to establish the effective use of bipolar host materials toward proficient solution-processable TADF-OLEDs.

New electron-acceptor cores are necessary for developing highly efficient bipolar hosts, particularly for blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Herein, chromenopyrazole (CP) was used for the first time as an electron-acceptor core to design and synthesize two novel blue bipolar hosts, viz., 8-(9H-carbazol-9-yl)-3-methyl-1-phenylchromeno[4,3-c]pyrazol-4(1H)-one (CzCP) and 8-(9H-[3,9′-bicarbazol]-9-yl)-3-methyl-1-phenylchromeno[4,3-c]pyrazol-4(1H)-one (2CzCP). The influence of donor strength on the photophysical, electrochemical, and electroluminescent performances was systematically investigated. CzCP and 2CzCP both maintain high triplet energy (∼3.0 eV), appropriate highest occupied and lowest unoccupied energy levels (HOMO/LUMO), and bipolar nature. Consequently, OLEDs containing CzCP as a host in the emissive layer exhibited state-of-the-art performance with external quantum efficiency of 27.9% and CIE color coordinates of (0.15, 0.21), thus achievin...

We successfully synthesized a wide-bandgap p-type copolymer, 3MT-Th-S, bearing alkylthio-substituted benzodithiophene (BDT) as a donor and methyl-3-thiophenecarboxylate (3MT) as a weak electron acceptor. The electron affinity of the sulfur atom in the 2-ethylhexylthio side chains tethered to the thiophene units induces a low-lying highest occupied molecular orbital (HOMO) energy level in the corresponding polymer. 3MT-Th-S displays a strong absorption band from 400 to 600 nm, resulting in a relatively wide optical bandgap. Thin films of 3MT-Th-S exhibit a prominent face-on orientation in the out-of-plane profile, which might be a favorable orientation for moving charge carriers in the vertical direction in polymer solar cells (PSCs). Non-fullerene PSCs based on 3MT-Th-S as the donor and an n-type small molecule (ITIC, ITIC-Me, or IMIDT) were fabricated, and their performance was investigated in detail. Among the PSC devices bearing three different acceptors, the 3MT-Th-S:ITIC-based PSC exhibits the highest power conversion efficiency of 7.86% with a high short-circuit current density of 16.11 mA cm−2 and an open circuit voltage of 0.96 V. The high PCE values of PSC using the as-cast blend films of 3MT-Th-S and ITIC as an active layer without solvent additive are attributed to the low-lying HOMO level of the donor polymer, the complementary absorption behavior of the blend film, the face-on arrangement of polymer chains on the substrate, and the well-formed morphology of the binary blend film. These results clearly demonstrate that 3MT-Th-S is a promising wide-bandgap p-type polymer for high-performance fullerene-free simple PSCs.

A new A-b-D-b-A-type n-type small molecule, IDT-3MT, was synthesized bearing a weak acceptor thiophene-3-carboxylate bridge (3MT = b) between indacenodithiophene as a donating core and 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile as the accepting end groups. Compared to IDT-T bearing a neat thiophene bridge, IDT-3MT displayed a red-shifted absorption spectrum in the film state, which is a more effective complementary absorption behavior with PBDB-T as the donor material. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of IDT-3MT became correspondingly lower. Based on the results of grazing-incidence wide-angle X-ray scattering, the blend film of PBDB-T:IDT-3MT exhibited a more prominent face-on orientation and fine surface morphology compared with PBDB-T:IDT-T, which can facilitate charge transportation in the vertical direction. Among the two acceptors, the polymer solar cell based on a solvent additive-free as-cast PBDB-T:IDT-3MT blend film exhibited the highest power conversion efficiency of 8.40% with a high open-circuit voltage of 0.95 V and a short-circuit current density of 14.43 mA cm−2 due to the more prominent face-on orientation and favorable morphology of the blend film. According to the simple structural modification of the acceptor molecule, the ester group in the thiophene bridge played an important role toward achieving high-performance polymer solar cells.

The importance of thermally activated delayed fluorescence (TADF) materials in organic light-emitting diode (OLED) applications continues to grow as a consequence of their unique properties and excellent performance. Herein, a new green-emitting TADF polymer, P(DMTRZ-Cp), for solution-processable OLEDs was designed and synthesized based on the structure of DMAC-TRZ that shows typical TADF characteristics as a small molecule. The 1,1-diphenylcyclohexane (Cp) moiety introduced into the structure of the polymeric emitter not only acts as a linker between the conjugated monomeric units, but also helps enhancing solubility while disconnecting conjugation along the polymer backbones. P(DMTRZ-Cp) exhibits obvious TADF features such as a small energy gap (0.023 eV) between its lowest singlet and triplet excited states, and obvious delayed photoluminescence (PL) decay behavior. Moreover, this new polymeric emitter exhibits high PL quantum yield over 90% in the film state. By applying solution-processed TADF-OLED devices, P(DMTRZ-Cp) exhibited the maximum external quantum efficiency of up to 15.4% with green emission. As far as we know, this is the first report to introduce a non-conjugated linker, Cp, in the main-chain type polymeric emitter structure that presents TADF characteristics. The Cp linker is considered to be a promising moiety for the development of solution-processable polymeric emitters with high efficiencies.

New versatile host materials with good solubility in common organic solvents are greatly desired to promote solution-processable thermally activated delayed fluorescence organic light-emitting diodes. This paper describes the design and synthesis of two new host materials, namely 3′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3,5-diylbis(diphenylphosphine oxide) (CDPO) and 3′,5′-di-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3,5-diylbis (diphenylphosphine oxide) (mCPDPO), featuring hole-transporting carbazole and electron-transporting diphenylphosphine oxide (DPO) entities. The donor strength was varied to a constant n-type DPO core to tune the functional properties. The detailed studies proved that the resulting two new materials exhibit excellent solubility in common organic solvents, high triplet energy (>2.80 eV), high glass transition temperature (up to 133 °C), and good bipolar electronic nature. Consequently, both compounds were used as hosts in solution-processable blue and green thermally activated delayed fluorescence (TADF) OLEDs. In particular, the devices using mCPDPO as a host in the emissive layer showed outstanding performance with a maximum current efficiency, power efficiency, and external quantum efficiency of 35.3 cd A−1, 17.0 lm W−1 and 15.4% in the blue-emitting diode, and 61.5 cd A−1, 29.7 lm W−1 and 18.8% in the green-emitting diode, respectively. These results corroborated the potential of carbazole-phosphine oxide derivatives as host materials in solution-processable blue and green TADF OLEDs.

In order to investigate the effect of the geometries of perylene diimide (PDI)-based small molecules, five different isomers were synthesized by using a cyclohexane core as a simple sp3-σ core. Diaminocylohexane is such an effective core for the systematic development of many kinds of isomers via geometric tuning as well as for reducing the self-aggregation tendency of PDIs. Depending on the anchoring position of the PDI units on the cyclohexane core (ortho-, meta- and para-), isomers exhibited differences in solubility and crystallinity. Among the studied isomers, ortho-substituted t-OCP was found to have a highly twisted molecular structure which minimizes the strong tendency towards crystallization due to individual PDI moieties. The unique geometrical nature of the t-OCP isomer led to the highest power conversion efficiency (PCE = 6.23%) of bulk heterojunction (BHJ) polymer solar cells (PSCs) with a higher short-circuit current density (Jsc) and fill factor (FF). It is mainly ascribed to the formation of a nanophase interpenetrating network with well-balanced carrier mobility in the blend film.

Three new derivatives containing silane cores, viz. 9,9′,9′′-(((4-(pyridin-3-yl)phenyl)silanetriyl)tris(benzene-4,1-diyl))tris(9H-carbazole) (SiCz3Py1), bis(4-(9H-carbazol-9-yl)phenyl)bis(4-(pyridin-3-yl)phenyl)silane (SiCz2Py2), and 9-(4-(tris(4-(pyridin-3-yl)phenyl)silyl)phenyl)-9H-carbazole (SiCz1Py3), were designed and synthesized. Carbazole as a donor and pyridine as an acceptor were tethered to tetraphenylsilane at different mole ratios. All three host materials showed high glass transition temperatures between 118 and 164 °C, which are different from those of the previous silane-based host materials (e.g., diphenyldi-o-tolylsilane (UGH-1), 1,4-bis(triphenylsilyl)benzene (UGH-2), and 1,3-bis(triphenylsilyl)benzene (UGH-3)). The triplet energies of these three hosts are observed at 2.85–2.90 eV, which is high enough for them to act as blue host materials in thermally activated delayed fluorescence organic light emitting diodes (TADF OLEDs). In particular, SiCz2Py2 and SiCz1Py3 hosted-TADF OLEDs demonstrated excellent performances, with a maximum external quantum efficiency (EQEmax) of 18.7 and 18.8%, respectively. Such good performances of SiCz2Py2 and SiCz1Py3 are originated by suppressing the non-radiative triplet decay and high reverse intersystem crossing (RISC) rate constant for efficient triplet to singlet up-conversion. This work demonstrates that tetraphenylsilane is a promising non-conjugate (i.e., sp3-hybridized) linkage core for developing a variety of high Tg host materials, particularly for blue TADF OLEDs.

To control the molecular energy levels of highly π-extended n-type molecules, we synthesized two acceptor–donor–acceptor (A–D–A)-type molecules with indacenodithiophenes (IDTs) or IDT–benzodithiophene (BDT)–IDT as donating cores and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile (IM) as terminal accepting units. These molecules showed different optical and electrochemical properties, indicating that the energy levels can be easily tuned by changing the structure of the donating core. Among two molecules, IM-BDTIDT2 showed a relatively blue shifted absorption spectrum and low-lying highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels. Although IM-IDT3 and IM-BDTIDT2 have a highly π-extended conjugated structure, no clear crystalline behaviour was observed in their thin films. When applied to polymer solar cells (PSCs), the device based on IM-BDTIDT2 displayed a higher PCE (5.33%) than the device bearing IM-IDT3 owing to the lower-lying energy levels of IM-BDTIDT2. Thus, the use of BDT as a donating core unit is favorable for limiting high-lying energy levels in highly π-extended A–D–A-type molecules.

Three A 1 -D-A 2 -D-A 1 -type conjugated molecules (A: acceptor, D: donor), containing diketopyrrolopyrrole (DPP) acceptors, another weaker acceptor, and thiophenes as common donors, were synthesized. The molecules exhibited strong absorption from 500 nm to the near-IR wavelength region, and different molecular energy levels. The three molecules synthesized were applied in solar cells made with phenyl-C 71 -butyric acid methyl ester, and thienopyrroledione (TPD) (DPP) 2 exhibited the highest power conversion efficiency of 3.37% owing to its appropriate internal morphology and relatively high open circuit voltage, which is conferred by its relatively low-lying highest occupied molecular orbital level.

Three A1-D-A2-D regular conjugated terpolymers containing diketopyrrolopyrrole, isoindigo, or thienoisoindigo moieties were synthesized. Each terpolymer with the combination of two different acceptors and thiophene as common donor displayed strong absorption from 500 nm to the near-IR region as well as different molecular energy levels. Among three terpolymers, bulk heterojunction polymer solar cell made of the terpolymer containing diketopyrrolopyrrole, isoindigo, and thiophene moieties and phenyl-C71-butyric acid methyl ester showed the highest power conversion efficiency of 6.95% due to its appropriate internal morphology and the high open circuit voltage conferred by the relatively low-lying highest occupied molecular orbital level of the polymer.

A light-emitting molecular triad (BPCP-2CPC) with dual functionality was successfully synthesized and applied to solution-processed non-doped organic light-emitting diodes. The BPCP-2CPC triad contains 9-phenyl-9H-carbazole units as a host moiety tethered to a green-emitting core (BPCP) through a cyclohexane unit and exhibits thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) characteristics simultaneously. The BPCP-2CPC-based non-doped TADF-OLED devices showed a high external quantum efficiency (EQE) of 13.4%.

Isoindigo-based copolymers containing non-fluorinated (PIIDBT) and fluorinated bithiophene moieties (PIIDFBT) were synthesized. The replacement of hydrogen atoms with electronegative fluorine atom attained the intramolecular noncovalent interactions in conjugated polymer structure employing the concept of conformational locks. Furthermore, the fluorine characteristics as substituent atoms tuned the electron withdrawing ability and made the HOMO energy levels of fluorinated moieties deeper (−5.79 eV) than that of non-fluorinated polymer (−5.54 eV). As a result, the photovoltaic performance of PIIDFBT was improved by increasing its open circuit voltage ( V oc ) up to 1.01 V, resulting in a power conversion efficiency of 6.21%. The PIIDFBT with high V oc can be recognized as a promising candidate for both single junction and multi-junction photovoltaics.

New M- and V-shaped perylene diimide (PDI)-based small molecules using a non-conjugated 1,1-diphenylcyclohexane linker (CP-M and CP-V, respectively) were designed and synthesized as new n-type acceptors for nonfullerene-based polymer solar cells. The blended film with poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) and CP-V displayed a higher power conversion efficiency of 5.28% due to higher short circuit current and fill factor values.

New bipolar host molecules composed of carbazole, pyridoindole, and dibenzothiophene (DBT) were synthesized for blue thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs). 2,8-Di(9H-carbazol-9-yl)dibenzo[b,d]thiophene, 9-(8-(9H-carbazol-9-yl)dibenzo[b,d]thiophen-2-yl)-9H-pyrido[2,3-b]indole, and 2,8-bis(9H-pyrido[2,3-b]indol-9-yl)dibenzo[b,d]thiophene were prepared based on the selective reactivity at the 2,8-positions of DBT. The new symmetric and asymmetric host materials exhibited high triplet energies (2.89–2.95 eV). 4,5-Di(9H-carbazol-9-yl)phthalonitrile (2CzPN) was selected as an emitting dopant for achieving sky-blue emissions in TADF-OLEDs. 2CzPN-doped TADF-OLEDs, whose configuration is ITO (50 nm)/HATCN (7 nm)/TAPC (75 nm)/host:6% 2CzPN (20 nm)/TmPyPB (50 nm)/LiF (15 nm)/Al (100 nm), showed low driving voltages and high external quantum efficiencies (EQEs). These results are attributed to the well-controlled bipolar character of the host giving a better charge balance in the emitting layer. In particular, the device containing ZDN:6% 2CzPN showed an unprecedentedly high EQE of 25.7% (at 0.074 mA cm−2).

Polyfluorene (PF)-based chiral alternating copolymers, i.e., PFPh and PFTh, were successfully synthesized to obtain high circular dichroism (CD) in pristine thin films. By tethering chiral side-chains to the fluorene moiety, the resultant PFPh and PFTh films intriguingly exhibited high CD even in pristine films, which was attributed to the relatively low steric hindrance between the repeating units and intermolecular interactions between the polymer chains. Compared to PFTh bearing a five-membered heteroaromatic thiophene monomer, PFPh containing a six-membered aromatic benzene monomer, showed significantly enhanced CD in an annealed film. Of particular importance, results of optical microscopy and atomic force microscopy can be used to assess the CD of a chiral polymer thin film after thermal annealing.

Conjugated polymers are of great interest and have been extensively examined as colorimetric and fluorometric sensors for biologically important species. Here, we report the systematic investigation of diketopyrrolopyrrole based conjugated polymers (PDTDPPT, PDTDPPSe and PDTDPPTe) bearing S, Se, and Te towards oxidative addition of Br2 using absorption spectroscopy, NMR spectroscopy, cyclic voltammetry, atomic force microscopy, and density functional theory calculations. PDTDPPTe polymer displays a highly sensitive, selective, and rapid response to Br2.

A series of bipolar host materials containing dibenzo[b,d]thiophene (DBT) or dibenzo[b,d]thiophene 5,5-dioxide core were successfully synthesized, and their physical, photophysical, and electrochemical properties were investigated. The three host materials showed well-localized electron distribution at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states, as evidenced by theoretical calculations. Triplet energies of the new host materials are higher than 2.6 eV, and the blend film with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as a blue phosphorescent dopant showed highly efficient energy transfer between the host material and dopant.

New large-bandgap host materials with carbazole and carboline moieties were designed and synthesized for high-performance blue phosphorescent organic light-emitting diodes (PhOLEDs). The two kinds of host materials, 9-(4-(9H-carbazol-9-yl)phenyl)-6-(9H-carbazol-9-yl)-9H-pyrido[2,3-b]indole (pP2CZCB) and 9-(3-(9H-carbazol-9-yl)phenyl)-6-(9H-carbazol-9-yl)-9H-pyrido[2,3-b]indole (mP2CZCB), displayed promisingly high triplet energies of ∼2.92–2.93 eV for enhancing the exothermic energy transfer to bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) in PhOLED devices. It was found that the blue PhOLEDs bearing the new host materials and the FIrpic dopant exhibited markedly higher external quantum efficiencies (EQEs) than a device made with 1,3-bis(N-carbazolyl)benzene (mCP) as the host. In particular, the PhOLED device made with 3 wt% FIrpic as the dopant and mP2CZCB as the host material displayed a low driving voltage of 4.13 V and the high EQE of 25.3% at 1000 cd m−2.

In this work, three-armed luminogens IAcTr-out and IAcTr-in were synthesized and used as emitters bearing triazine and indenoacridine moieties in thermally activated delayed fluorescence organic light-emitting diodes (OLEDs). These molecules could form a uniform thin film via the solution process and also allowed the subsequent deposition of an electron transporting layer either by vacuum deposition or by an all-solution coating method. Intriguingly, the new luminogens displayed aggregation-induced emission (AIE), which is a unique photophysical phenomenon. As a nondoped emitting layer (EML), IAcTr-in showed external quantum efficiencies (EQEs) of 11.8% for the hybrid-solution processed OLED and 10.9% for the all-solution processed OLED with a low efficiency roll-off. This was evident by the higher photoluminescence quantum yield and higher rate constant of reverse intersystem crossing of IAcTr-in, as compared to IAcTr-out. These AIE luminogens were used as dopants and mixed with the well-known host material 1,3-bis( N-carbazolyl)benzene (mCP) to produce a high-efficiency OLED with a two-component EML. The maximum EQE of 17.5% was obtained when using EML with IAcTr-out doping (25 wt %) into mCP, and the OLED with EML bearing IAcTr-in and mCP showed a higher maximum EQE of 18.4% as in the case of the nondoped EML-based device.

Two novel donor-π-acceptor (D-π-A type) porphyrin dyes were successfully synthesized and use in a dye-sensitized solar cell (DSSC). The molecular structures of both porphyrins are composed of the same dialkyl-substituted diphenylamino unit acting as the donor part, and two bisalkoxyphenyl substituents at the 5,15-meso positions. The acceptor part is composed of different ethyne-linked π-extended bridges, and a cyanoacrylic acid (Dye I) or carboxyphenyl (Dye II) moiety acting as anchoring groups. In order to investigate the effects of including the π-extended bridge between the porphyrin and acceptor unit, two different π-extended bridges such as 2,2′-bithiophene and 2-(phenylethynyl)-thiophene, were employed. In particular, Dye II contains two triple bonds between donor substituted porphyrin and carboxylic acid group. These modifications could potentially reduce dye aggregation on the TiO 2 surface. The charge recombination resistance and diffusion length for the cells with Dye II were relatively higher for all the measured ranges of bias potentials, implying that electron recombination loss from injected electrons was highly suppressed when Dye II molecules were adsorbed on the TiO 2 surface. Eventually, Dye II containing a 2,2′-bithiophene π-spacer and anchored trough a carboxyphenyl group exhibited a superior power conversion efficiency of 6.7% under AM 1.5 illumination (100 mW.cm-2) in a photoactive area of 0.46 cm2 than Dye I with a 2-(phenylethynyl)thiophene (PCE = 3.5%) anchored through a cyanoacrylic group.

Novel two-dimensional π-conjugated molecules, i.e., 5′,5″′-((9,10-bis((4-hexylphenyl)ethynyl)anthracene-2,6-diyl)bis(ethyne-2,1-diyl))bis(5-hexyl-2,2′-bithiophene) (2,6-HBT) and 5′,5″′-((2,6-bis((4-hexylphenyl)ethynyl)anthracene-9,10-diyl)bis(ethyne-2,1-diyl))bis(5-hexyl-2,2′-bithiophene) (9,10-THB) were successfully synthesized and utilized as highly soluble p-type organic semiconductors for organic thin film transistors (TFTs) and solar cells. From the TFTs, the high hole mobility of the pristine film of 9,10-THB was measured to be 0.07 cm2 V−1 s−1 (Ion/off = 106–107), which is mainly attributed to slip-stacked charge-transport behavior in J-aggregation-induced crystallites. Further, a solution-processed solar cell made of 9,10-THB and PC61BM exhibited very promising and reproducible power conversion efficiencies of 3.30% and 2.53% with composition 1:1 and 1:2 w/w ratio, respectively.

A diketopyrrolopyrrole derivative was synthesized and designed with two trimethylsilyl groups to allow for sensitive, selective and fast recognition of fluoride ions by using a chemodosimeter approach. The probe exhibited a blue shift in the absorption and emission spectra in the presence of fluoride ions due to deprotection of the electron donating trimethylsilyl groups in the probe. UV–vis absorption, fluorescence, density functional theory and cyclic voltammetry studies indicated fluoride triggered cleavage of the Si–C bond resulting in the blue spectral shift.

Correlation between the photovoltaic activity and adsorption characteristics of a TiO 2 electrode coated with an organo-dendritic dye containing three chromophores in one molecule ((2 E ,2′ E ,2″ E )-3,3′,3″-(10,10′,10″-(6,6′,6″-(4,4′,4″-(ethane-1,1,1-triyl)tris(benzene-4,1-diyl))tris (oxy)tris(hexane-6,1-diyl))tris(10 H -phenothiazine-10,3-diyl))tris(2-cyanoacrylic acid), triple-PTZ) was investigated by applying it in dye-sensitized solar cells (DSSCs). The photovoltaic performance of the DSSCs utilizing the Triple-PTZ dyes varied based on the solvent conditions employed for adsorbing the dye on the TiO 2 electrode surface. Aggregation of the Triple-PTZ dyes on the electrode surface was induced in the poor solvent system, with a consequent increase in the total amount of Triple-PTZ dye, which is directly adsorbed on the TiO 2 surface. However, incomplete tethering of the Triple-PTZ dye molecules onto the TiO 2 surface substantially reduced the short-circuit current ( J sc ). A good solvent promoted uniform adsorption of the Triple-PTZ dye on the TiO 2 surface, with a consequent enhancement of the power conversion efficiency (PCE) of the fabricated DSSCs up to 4.90%, which is much higher than the PCE of 1.93% obtained from the DSSC fabricated using the poor solvent system. The correlation between the adsorption properties of the photosensitizing Triple-PTZ dyes on the TiO 2 electrode and the photovoltaic performance was intensively investigated with the help of ATR-FT-IR spectroscopy, the incident photon-to-electron conversion efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) analysis.

A reversible probe based on diketopyrrolopyrrole–tellurophene conjugate for the detection of reactive oxygen species has been designed and synthesized. The probe utilizes the redox properties of the tellurium atom for the detection of reactive oxygen species and exhibits high selectivity and sensitivity towards H 2 O 2 ; the presence of which is demonstrated by a fluorescent signal. In addition to fluorescence signal, the probe displayed a color change from light blue to light purple upon oxidation by H 2 O 2 in aqueous media. The generated tellurophene-1-oxide may be quickly reduced by glutathione to regenerate the original diketopyrrolopyrrole–tellurophene conjugate. The probe can be applied to monitor the concentration of H 2 O 2 in aqueous solution over an approximate pH range 3.8–8.0.

We designed and synthesized a series of phenothiazine-based donor–acceptor type molecules which consist of different numbers of chromophores in a molecule for use as photosensitizers for dye-sensitized solar cells (DSSCs). Intriguingly, a dendritic molecule containing three chromophores not only gave a new possibility to modify the three dimensional structure, but also reduced aggregation between chromophores inducing dipole–dipole interaction. The DSSCs made of a dendritic photosensitizer system exhibited much higher cell efficiencies than those with the single- or double-chromophoric photosensitizers due to efficient electron extraction pathways in the dendritic molecule which lead to a significantly reduce recombination rate of electrons from the TiO2 to the electrolyte when the same numbers of chromophores were loaded on the TiO2 surface. In particular, the DSSC based on the dendritic molecule exhibited improved open-circuit voltage than that of the single- or double-chromophoric photosensitizers. This can be attributed to strong adsorption properties of the TiO2 electrode and a screening effect to the electrolyte ions provided by the network structure of the dendritic photosensitizer. The different behavior of these DSSCs was explained by comparing the results of electrochemical impedance spectroscopy and measurement of open-circuit voltage decay.

Two new metal-free organic dyes bridged by anthracene-mediated π-conjugated moieties were successfully synthesized for use in a dye-sensitized solar cell (DSSC). A N,N-diphenylthiophen-2-amine unit in these dyes acts as an electron donor, while a (E)-2-cyano-3-(thiophen-2-yl)acrylic acid group acts as an electron acceptor and an anchoring group to the TiO2 electrode. The photovoltaic properties of (E)-2-cyano-3-(5-((10-(5(diphenylamino)thiophen-2-yl)anthracen-9-yl)ethynyl)thiophen-2-yl)acrylic acid (DPATAT) and (E)-2cyano-3-(5'-((10-(5-(diphenylamino)thiophen-2-yl)anthracen-9-yl)ethynyl)-2,2'-bithiophen-5-yl)acrylic acid (DPATABT) were investigated to identify the effect of conjugation length between electron donor and acceptor on the DSSC performance. By introducing an anthracene moiety into the dye structure, together with a triple bond and thiophene moieties for fine-tuning of molecular configurations and for broadening the absorption spectra, the short-circuit photocurrent densities (Jsc), and open-circuit photovoltages (Voc) of DSSCs were improved. The improvement of Jsc in DSSC made of DPATABT might be attributed to much broader absorption spectrum and higher molecular extinction coefficient (e) in the visible wavelength range. The DPATABT-based DSSC showed the highest power conversion efficiency (PCE) of 3.34% (ηmax = 3.70%) under AM 1.5 illumination (100 mW cm �2 ) in a photoactive area of 0.41 cm 2 , with the Jsc of 7.89 mA cm �2 , the Voc of 0.59 V, and the fill factor (FF) of 72%. In brief, the solar cell performance with DPATABT was found to be better than that of DPATAT-based DSSC.

New Donor-σ-acceptor (D-σ-A) molecules of (HAT)-2(PDI) and (HAT)-2(PCBM); PDI refers to perylene diimide, PCBM refers to [6,6]-phenyl C61-butyric acid methyl ester, and HAT refers to 5,5′-(9,10-bis((4-hexylphenyl)ethynyl)anthracene-2,6-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene) were successfully synthesized for studying the intermolecular association behavior and their possible applications of these molecules to electrically bistable devices. The memory devices with the configuration of Al/(HAT)-2(PDI) or (HAT)-2(PCBM)/ITO exhibited a low-voltage operating flash type memory capability.

Novel two-dimensional X-shaped donor–π–acceptor (D–π–A)-type dyes were designed and successfully synthesized for use in a dye-sensitized solar cell (DSSC). Two triphenylamine units in these dyes act as electron donor units, while two cyanoacrylic acid groups act as electron acceptor units and anchoring groups to the TiO 2 photoanode. The photovoltaic properties of the newly synthesized dye-containing DSSCs were investigated to identify the effects of conjugation length between the electron donors and acceptors, and the molecular energy levels of the dyes. Among the three dyes we synthesized, (2E,2′E)-3,3′-(5′,5″-(4,5-bis(4-(bis(4-tert-butylphenyl)amino)styryl)-1,2-phenylene)bis(2,2′-bithiophene-5′,5-diyl))bis(2-cyanoacrylic acid) ( 11 ) showed the highest power conversion efficiency of 3.14% ( η max = 4.06% with TiCl 4 treatment) under AM 1.5G illumination (100 mW cm −2 ) in a photoactive area of 0.418 cm 2 with short circuit current density of 7.27 mA cm −2 , open circuit photovoltage of 612 mV, and a fill factor of 70.6%.

A new anthracene-containing conjugated molecule was synthesized through the Sonogashira coupling and reduction reactions. 1-Ethynyl-4-hexylbenzene was coupled to 2,6-bis((4-hexylphenyl) ethynyl)anthracene-9,10-dione through a reduction reaction to generate 2,6,9,10-tetrakis((4-hexylphenyl)ethynyl) anthracene. The semiconducting properties were evaluated in an organic thin film transistor (OTFT) and a single-crystal field-effect transistor (SC-FET). The OTFT showed a mobility of around 0.13 ( > ), whereas the SC-FET showed a mobility of 1.00-1.35 , which is much higher than that of the OTFT. Owing to the high photoluminescence quantum yield of 2,6,9,10-tetrakis((4-hexylphenyl)ethynyl) anthracene, we could observe a significant increase in drain current under irradiation with visible light ( = 538 nm, 12.5 ).

Tricyanofuran-based small molecules were synthesized through Knoevenagel reaction with formyl heteroaromatic donating moieties and 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as a strong acceptor. UV–vis absorption demonstrated that the combination of TCF with donating units resulted in an enhanced intra-molecular charge transfer (ICT) transition, which led to long wavelength absorption in the chromophores. The absorption coefficients and the molecular energy levels of the chromophores can be tuned effectively by employing different donating groups. The chromophores were used in conjunction with [6,6]-phenyl C61 butyric acid methyl ester (PC 61 BM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) to fabricate organic heterojunction photovoltaic cells. This solution-processed bulk heterojunction (BHJ) solar cells exhibited a power conversion efficiency (PCE) of 2.44%, a short-circuit current density ( J SC ) of 8.74 mA/cm 2 , and an open-circuit voltage ( V OC ) of 0.93 V under simulated air mass 1.5 global irradiation (100 mW/cm 2 ).

A hole-injection/transport bilayer structure on an indium tin oxide (ITO) layer was fabricated using two photocrosslinkable polymers with different molecular energy levels. Two photoreactive polymers were synthesized using 2,7-(or 3,6-)-dibromo-9-(6-((3-methyloxetan-3-yl)methoxy)hexyl)-9H-carbazole) and 2,4-dimethyl-N,N-bis(4- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline via a Suzuki coupling reaction. When the oxetane groups were photopolymerized in the presence of a cationic photoinitiator, the photocured film showed good solvent resistance and compatibility with a poly(N-vinylcarbazole) (PVK)-based emitting layer. Without the use of a conventional hole injection layer (HIL) of poly(3,4-ethylenedioxythiophene)/(polystyrenesulfonate) (PEDOT:PSS), the resulting green light-emitting device bearing PVK: 5-4-tert-butylphenyl-1,3,4-oxadiazole (PBD):Ir(Cz-ppy)3 exhibited a maximum external quantum efficiency of 9.69%; this corresponds to a luminous efficiency of 29.57 cd/A for the device K-4 configuration ITO/POx-I/POx-II/PVK:PBD:Ir(Cz-ppy)3/triazole/Alq3/LiF/Al. These values are much higher than those of PLEDs using conventional PEDOT:PSS as a single HIL. The significant improvement in device efficiency is the result of suppression of the hole injection/transport properties through double-layered photocrosslinked-conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Novel donor–acceptor (D–A) type cruciform dyes were synthesized for use in a dye-sensitized solar cell. The geometries and electronic structures of the dyes were designed by the results of density functional theory (DFT) calculations. Two phenothiazine units in these dyes act as electron donors, while two cyanoacrylic acid groups act as electron acceptors. The solubility of these compounds is increased because of the presence of the hexyl groups in the phenothiazine rings. The photovoltaic properties of 14D-25A and 12A-45D were measured to identify the effects of the dye having two electron donors and two electron acceptors on the DSSC performance. The 12A-45D dye showed a power conversion efficiency of 4.5% under AM 1.5 illumination (100 mW cm −2 ) in an photoactive area of 0.42 cm 2 , short circuit current density of 10.8 mA cm −2 , open circuit photovoltage of 0.65 V and a fill factor of 64%.

A functionalized deoxyribonucleic acid (Cz-DNA) was prepared with carbazolyl ammonium lipid as a triplet host material for phosphorescent material system. It is soluble in organic solvents, which facilitates the sample preparation for the absorption and luminescent properties in solid states. A highly soluble iridium complex, Ir(Cz-ppy)3 with carbazolyl-substituted 2-phenylpyridine ligands was employed for studying the phosphorescence in Cz-DNA. There is a good overlap between the photoluminescence spectrum of Cz-DNA and the metal-to-ligand charge transfer (MLCT) absorption bands of the iridium complex. This overlap enables efficient energy transfer from the excited state in the host to the MLCT band of Ir(Cz-ppy)3. In addition, photoluminescence quantum yield of Cz-DNA was found to be relatively larger than the copolymer (PCzSt) with vinylcarbazole and styrene. Thus, Cz-DNA was employed as a triplet host material for fabricating multilayered electrophosphorescence devices via modification of its property by doping 5,4-tert-butylhexyl-1,3,4-oxadiazole (PBD). After doping 30 wt % PBD and 10 wt % Ir(Cz-ppy)3 into Cz-DNA, we achieved much improvement in electron injection/transport from an adjacent carrier transport layer, resulting in much improved device performances. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1913–1918, 2010

9-((6-Phenylpyridin-3-yl)methyl)-9H-carbazole and 9-((6-(4-fluorophenyl)pyridin-3-yl)methyl)-9H-carbazole were synthesized as ligands by attaching a carbazolyl group to the pyridine in 2-phenylpyridine and 2-(4-fluorophenyl)pyridine, respectively. Four different Ir(III) complexes were prepared using a simple procedure, the solubility of which was significantly greater than that of conventional green-emitting Ir(ppy)3. Among the many devices fabricated, that which contained 10% of Ir(Cz-ppy)1(Cz-Fppy)2 in PVK/PBD (70:30 wt%), exhibited an external quantum efficiency of 6.80%, luminous efficiency of 20.23 cd/A, and maximum brightness of 17520 cd/m2. In particular, the electronic property of the new 9-((6-(4-fluorophenyl)pyridin-3-yl)methyl)-9H-carbazole ligand can manipulate the triplet energy level of the Ir(III) complex to finely tune the emission spectra.

New anthracene-containing conjugated molecules have been synthesized through Stille coupling reaction. 2,6-Dibromoanthracene-9,10-dione was reacted with ethynylbenzene or 1-ethynyl-4-hexylbenzene to yield 2,6-dibromo-9,10-bis(phenylethynyl)anthracene 4 and 2,6-dibromo-9,10-bis((4-hexylphenyl) ethynyl)anthracene 5. Tributyl(5-hexylthiophen-2-yl)stannane was coupled through Stille reaction to generate two anthracene-based X-shaped molecules. They exhibit good solubility in common organic solvents and good self-film-forming properties. The semiconducting properties of the two molecules were evaluated in organic thin film transistors (OTFTs). Two conjugated molecules 7 and 8 exhibit fairly high charge carrier mobilities—as high as 0.010–0.014 cm2 V−1 s−1 (Ion/Ioff = 1.27 × 107 to 4.38 × 106) without thermal annealing process. The X-shaped molecules result in easy crystallization and densely cover the surface of a dielectric layer. This helps in attaining good network interconnection for the carrier transport channel, which is responsible for the relatively high carrier mobility in solution-processed OTFT.

The preparation of organic-soluble DNA bearing carbazole side chain (Cz-DNA) was carried out and the resulting Cz-DNA shows good solubility in alcohol, which allows the fabrication of thin films fo...

Donor-σ-acceptor molecules of HPBT- n (PDI) ( n = 1, 2, and 4) containing perylene diimide (PDI) and π-extended 1,2,4,5-tetrakis((E)-2-(5′-hexyl-2,2′-bithiophen-5-yl)vinyl)benzene (HPBT) have been successfully synthesized for studying the self-organization of each moiety and their applications in photovoltaic devices. Interesting features were found in these molecules: the aggregation-induced crystallization in the HPBT moieties enhanced the power conversion efficiency (PCE) in the photovoltaic cell. By incorporating HPBT as the donor and PDI as the acceptor moiety, we anticipated that their high degree of independent aggregation-induced crystallization would yield electron/hole transport channels and high mobility in the desired direction of charge transport. In a photovoltaic device, HPBT-1(PDI) gave a PCE of 0.22% with an open circuit voltage ranging from 0.62 to 0.63 V. When the HPBT moiety was more hindered by the PDI moiety, less PCE was observed in HPBT-2(PDI). Addition of methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) resulted in enhancement of the PCE due to enhanced visible absorption. The device bearing HPBT-1(PDI) and PCBM (1:4 mol ratio) demonstrate much higher PCE to be around 1.60%.

The ligands, 9-((6-phenylpyridin-3-yl)methyl)- 9H -carbazole and 9-(4-(pyridin-2-yl)benzyl)- 9H -carbazole were synthesized by attaching a carbazolyl group to the pyridine and phenyl rings of 2-phenylpyridine, respectively. Ir(III) complexes were prepared by a simple procedure and the solubility of the novel complexes was significantly better than that of the conventional, green-emitting conventional fac -tris(2-phenylpyridinato-C 2 ,N)iridium(III). The Ir(III) complexes were used to prepare electrophosphorescent polymer light-emitting devices. The device comprising 10% of fac -tris(2-(4′-((9 H -carbazol-9-yl)methyl)phenyl)pyridinato-C 2 ,N)iridium(III) exhibited an external quantum efficiency of 7.88%, luminous efficiency of 23.01 cd/A, and maximum brightness of 32,640 cd/m 2 . The color of the emissions of fac -tris(2-(4′-((9 H -carbazol-9-yl)methyl)phenyl)pyridinato-C 2 ,N)iridium(III) was similar to that of conventional fac -tris(2-phenylpyridinato-C 2 ,N)iridium(III). This work shows that integration of a rigid hole-transporting carbazole and phosphorescent complex in one molecule provides a new route to highly efficient, solution-processable complexes for electrophosphorescent applications.