Diketopyrrolopyrrole Units Research Articles

Diketopyrrolopyrrole-triggered low exciton binding energy in D-A covalent organic framework for enhanced uranyl photoreduction

Construction of donor–acceptor covalent organic framework (D-A COFs) photocatalysts is regarded as promising path to promote photocatalytic reduction of uranium, but faces greater challenge due to high exciton binding energies (Eb). In this work, we construct a D-A COF (named Py-DPP-COF) with dye diketopyrrolopyrrole (DPP) unit as acceptor to minimize the Eb (56.5 meV). Importantly, experimental and computational studies reveal that DPP unit as adsorption and photocatalytic active sites play a pivotal role for catalyzing photoreduction of UVI to UIV. The Py-DPP-COF not only broadens the visible light absorption and promotes charge transfer, but also enhances interfacial mass transfer, achieving a higher uranium extraction capacity of 903.6 mg g−1. To our knowledge, this is the first application of DPP-based COFs for photocatalytic reduction of uranium, which greatly inspires the exploration of novel COFs photocatalysts for photo-induced radionuclide removal.

Neutral and Anion Species of Quinoidal Thienothiophene Diketopyrrolopyrroles Display a Common Aggregation Mode.

A comprehensive investigation of two new molecular triads incorporating the diketopyrrolopyrrole unit into a quinoidized thienothiophene skeleton, which is further end-capped with dicyanomethylene (DPP-TT-CN) or phenoxyl groups (DPP-TT-PhO), has been carried out. A combination of UV-Vis-NIR and infrared spectroelectrochemical techniques and cryogenic UV-Vis-NIR absorption spectroscopy supported by theoretical calculations has been used. The main result is the formation of similar H-aggregates in the dimerization process of the neutral molecules and of the charged anionic species. The experimental absorption spectra of the aggregated species are accurately reproduced by quantum chemical calculations using the Spano's model, including excitonic coupling for the dimeric forms and full vibronic resolution of the absorption bands. The strong excitonic coupling taking place is key to understand the electronic structure of the dimeric species and has been instrumental to disentangle the type of H-aggregation. This study is of relevance to get a better understanding of the molecular aggregation of organic π-conjugated chromophores and is useful as a guideline for the refinement of the engineering of molecular materials for which supramolecular design is required.

Asymmetrical Diketopyrrolopyrrole Derivatives with Improved Solubility and Balanced Charge Transport Properties.

The diketopyrrolopyrrole (DPP) unit represents one of the building blocks more widely employed in the field of organic electronics; in most of the reported DPP-based small molecules, this unit represents the electron acceptor core symmetrically coupled to donor moieties, and the solubility is guaranteed by functionalizing lactamic nitrogens with long and branched alkyl tails. In this paper, we explored the possibility of modulating the solubility by realizing asymmetric DPP derivatives, where the molecular structure is extended in just one direction. Four novel derivatives have been prepared, characterized by a common dithyenil-DPP fragment and functionalized on one side by a thiophene unit linked to different auxiliary electron acceptor groups. As compared to previously reported symmetric analogs, the novel dyes showed an increased solubility in chloroform and proved to be soluble in THF as well. The novel dyes underwent a thorough optical and electrochemical characterization. Electronic properties were studied at the DFT levels. All the dyes were used as active layers in organic field effect transistors, showing balanced charge transport properties.

Novel Beta-Functionalized Porphyrins Approaching 11% Efficiency for Organic Solar Cells.

Porphyrins and their derivatives possess high molar extinction coefficients and strong electron-donating abilities and have been widely used in organic solar cells (OSCs). Though porphyrins can be easily functionalized at the four meso-positions and the eight β-positions, nearly all porphyrin photovoltaic materials are reported to be functionalized at the meso-positions, and the porphyrin photovoltaic materials functionalized at the β-positions are to be explored. Herein, the regioselective β-positions of a porphyrin are first brominated without using rare metal iridium catalysts, and then, after two more reactions, two antipodal β-substituted porphyrin donors EHDPP-Por and BODPP-Por are synthesized, in which four DPP (diketopyrrolopyrrole) units are connected symmetrically with acetylene at four of the β-positions, for OSCs. The all-small-molecule organic solar cells based on EHDPP-Por:Y6 and BODPP-Por:Y6 active layers achieved power conversion efficiencies of 10.19 and 10.99%, respectively, which are higher than most of the binary OSCs based on the porphyrins functionalized at the meso-positions, demonstrating that β-functionalized porphyrins are very promising for OSCs.

An A-D-A'-D-A-Type Narrow Bandgap Electron Acceptor Based on Selenophene-Flanked Diketopyrrolopyrrole for Sensitive Near-Infrared Photodetection.

Near-infrared organic photodetectors possess great application potential in night vision, optical communication, and image sensing, but their development is limited by the lack of narrow bandgap organic semiconductors. A-D-A'-D-A-type molecules, featuring multiple intramolecular charge transfer effects, offer a robust framework for achieving near-infrared light absorption. Herein, we report a novel A-D-A'-D-A-type narrow bandgap electron acceptor named DPPSe-4Cl, which incorporates a selenophene-flanked diketopyrrolopyrrole (Se-DPP) unit as its central A' component. This molecule demonstrates exceptional near-infrared absorption properties with an absorption onset reaching 1120 nm and a low optical bandgap of 1.11 eV, owing to the strong electron-withdrawing ability and quinoidal resonance effect induced by the Se-DPP unit. By implementing a doping compensation strategy assisted by Y6 to reduce the trap density in the photoactive layer, the optimized organic photodetector based on DPPSe-4Cl exhibited efficient spectral response and remarkable sensitivity in the range of 300-1100 nm. Particularly, a specific detectivity surpassing 1012 Jones in the wavelength range of 410-1030 nm is achieved. This work offers a promising approach for developing highly sensitive visible to near-infrared broadband photodetection technology using organic semiconductors.

Carbazole-alt-fluorene based π-conjugated Cu(II)-metallopolymer with pendent diketopyrrolopyrrole unit as highly selective and sensitive turn-on fluorescent probe for detection of amino acids

Highly emissive and soluble poly(carbazole-alt-fluorene) (P1) based π-conjugated alternative copolymers with thiophene-diketopyrrolopyrrole as pendent unit have been designed and synthesized via Pd(0)-catalyzed Suzuki coupling polymerization from the corresponding monomers 3,6-dibromo-9H-carbazol-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole and 2,7-bis-oxaborolan-9,9-dioctylfluorene. The well-defined copolymer P1 has been characterized by multinuclear NMR spectra as well as by tetradetector GPC showing molecular weight (Mn) of 15.6 kg/mol with the polydispersity indices of 1.38. The red emissive polymer has been explored for the detection of amino acids based on a secondary ‘‘turn-on’’ sensing approach. The thiophene-diketopyrrolopyrrole anchored carbazole-alt-fluorene copolymer shows high selectivity towards Cu2+ ions by changing the emission wavelength from red to blue due to the formation of the Cu(II)-metallopolymer (P1–Cu2+). The resulting metallopolymer P1–Cu2+ exhibits high sensitivity and selectivity towards amino acids over the other biologically relevant analytes. More importantly, the P1–Cu2+ metallopolymer exhibited higher sensitivity towards glycine, with the detection limit of 90 ppb (∼1.21 × 10−6 mol/L) along with relatively higher association constant of 2.55 × 108 M−1. To comprehend the sensing mechanism through photo-induced electron transfer (PET), the detailed photophysical studies have been carried out with P1 and its representative monomeric model compound M1. Furthermore, fluorescence anisotropy study has also been carried out to inspect the molecular interactions responsible for the sensing properties of P1–Cu2+ metallopolymer towards glycine.

Fine-tuning the color hue of the solution-processable electrochromic copolymers based on the diketopyrrolopyrrole, benzodithiophene and dithienosilole units

Electrochromic materials (ECMs) have attracted increasing attentions on account of their extensive prospects and numerous demands. Here, the classical donor-acceptor (D-A) alternative copolymerization strategy was used to synthesize three kinds of novel conjugated polymers PBPS-1, PBPS-2, and PBPS-3. The diketopyrrolopyrrole (M1) unit with a long alkyl side-chain was employed as the core acceptor while the dithienosilole (M2) used as the donor units. More importantly, the benzodithiophene (M3) units which have the high skeleton coplanarity was selected as the bridge units to enhance the charge transport. Variations of the feed ratios of monomers was used to regulate the energy level and spectral absorption range of the solid films. Three polymers exhibited the abundant color hues in the redox process, which including grape purple/brownness/aircraft ash color (PBPS-1), dark grey/red soap/dusty blue color (PBPS-2) and marine blue/grayish/celadon color (PBPS-3). Electrochromic performances demonstrated that PBPS-2 possessed the fast discoloration speed as low as 0.26 s and the outstanding coloration efficiency (550.1 cm2·C−1), which portended a valuable material for smart ECMs applications. Furthermore, the effect of different feed ratios for three polymer in electrochemical, optical and kinetic properties were investigated in detail, which showed the satisfactory optical contrasts (>70% in the NIR region) and good kinetic stability (>97% retention in 1000 s). In general, this exploration supplied a handy design strategy for fine tuning of polymer color and conducive to strengthen the understanding of EC behaviors of the ternary polymers, which deserve further researches to explore more promising ECMs.

Stretchable Semiconducting Polymers with Hydrogen-Bonding-Capable Conjugation Breakers: Synthesis and Application in Organic Thin-Film Transistors.

Diketopyrrolopyrrole (DPP)-based conjugated copolymers are important organic semiconductors for applications in high-efficiency organic thin-film transistors (OTFTs). However, the direct application of these polymers with rigid backbones in stretchable devices has limitations. In this study, we designed and synthesized three kinds of DPPBT-based copolymers, DPPBT-A1, DPPBT-A3, and DPPBT-A5, which have amide-coupled alkylene conjugation breakers capable of hydrogen bonding. Linkers with different segment lengths were copolymerized with DPP and bithiophene (BT) backbone units. A DPP-based copolymer with alternating BT moieties, DPPBT, was synthesized as a reference fully conjugated copolymer. The synthesized polymers with freely rotational backbone linkers have sufficient flexibility to develop ordered phase domains, even in thin films, in comparison to the reference copolymer. However, the introduction of the conjugation breakers, which disconnect the intramolecular π-π overlapping, tends to decrease the hole mobility (μ) from 0.76 to 0.20 cm2 V-1 s-1 in the corresponding OTFT devices. The TFT fabricated using DPPBT-A3 showed a mobility of 0.50 cm2 V-1 s-1, and the mobility value did not show a significant change even when elongated by more than 50%. Therefore, the molecular design strategy of introducing amide-coupled alkylene conjugation breakers into conjugated polymer chains can contribute significantly to the development of high-mobility stretchable conjugated polymers in future.

(Invited) Non-Polymer Organic Solar Cells: Microscopic Phonon Control to Suppress Non-Radiative Voltage Loss Via Charge-Separated State

Recent remarkable developments on non-fullerene solar cells have reached photoelectric conversion efficiency (PCE) of 18% by tuning the band energy levels in small molecular acceptors. In this respect, development of the small donor molecule is essential. Although several methods have been applied to elucidate the elementary processes of charge carriers in BHJ-OSCs, mechanistic details of non-radiative voltage loss are poorly understood originating from interfacial heterogeneous electron-hole pairs.A recent time-resolved electron paramagnetic resonance (TREPR) study suggested an impact of the recombination process generating the triplet excitons in non-fullerene acceptor solar cells,[1] while geometries and motions of charge-separated (CS) states were elucidated in details by electron spin polarization (ESP).[2-4] Furthermore, although effects of low-frequency nuclear motions (phonon) on the photocarrier generations have been discussed in several literatures,[2,5,6] microscopic origin of the phonon playing a role on the OPV performance is unclear including impact of the phonon assist on primary recombination processes. Here we systematically investigated mechanisms of solar cell performance with diketopyrrolopyrrole (DPP)–tetrabenzoporphyrin (BP) conjugates of C4-DPP–H2BP and C4-DPP–ZnBP where C4 represents butyl group substituted at the DPP unit as small p-type molecules in non-polymer organic solar cells (OSC) with an acceptor of [6,6]-phenyl-C61-buthylic acid methyl ester. We clarified microscopic origins of the photocarrier caused by phonon-assisted 1D electron-hole dissociations at donor:acceptor interface. Using a time-resolved electron paramagnetic resonance, we have characterized controlled charge-recombination by manipulating disorders in π-π donor stacking, ensuring carrier transport through face-on molecular conformations to suppress non-radiative voltage loss via capturing specific interfacial radical pairs separated by 1.8 nm in bulk-heterojunction solar cells. While disordered lattice motions from the π-π stackings via zinc ligation are essential to enhance the entropy for charge-dissociations at the interface, too much ordered crystallinity causes backscattering phonon to reduce OSC performances.

Doped/Undoped A1‐A2 Typed Copolymers as ETLs for Highly Efficient Organic Solar Cells

AbstractThe electron transport layer (ETL) is a critical component in achieving high device performance and stability in organic solar cells. Conjugated polyelectrolytes (CPEs) have become an attractive alternative due to film‐forming properties and ease of preparation. However, p‐type CPEs generally exhibit poor charge mobility and conductivity, incorporation of electron‐withdrawing units forming alternated D‐A conjugated backbone can make up for these deficiencies. Herein, the ratio of electron withdrawing moieties are further increased and two poly(A1‐alt‐A2) typed PIIDNDI‐Br and PDPPNDI‐Br based on the combination of naphthalene diimide (NDI) with isoindigo (IID) or diketopyrrolopyrrole (DPP) via direct arylation polycondensation are synthesized. These CPEs possess excellent alcohol solubility, a suitable lowest unocuppied molecular orbital energy level, and work function tunability. Surprisingly, the incorporation of IID and DPP units generate distinct self‐doping behaviors, which are confirmed by UV–vis absorption and ESR spectra. However, no matter doped or undoped, both CPEs present better charge‐transporting properties and conductivity when utilized as ETLs. The PIIDNDI‐Br and PDPPNDI‐Br display good universal compatibility with the blend of PM6:Y6 and PM6:L8‐BO, and PCEs of 18.32% and 18.36% are obtained, respectively, which also present excellent storage stability. In short, the combination of two different acceptors demonstrates an efficient strategy to design highly efficient ETLs for high performance photovoltaic devices.

Realizing p‐Type and n‐Type Doping of a Single Conjugated Polymer via Incorporation of a Thienoisatin‐Terminated Quinoidal Unit

AbstractSelective doping of a single conjugated polymer (CP) to obtain p‐type and n‐type conductive materials would be highly attractive for organic thermoelectric applications, because it will greatly reduce the time and costs of synthesizing different types of CPs. However, this strategy has rarely been investigated. In this study, two CPs are synthesized, designated PTQDPP‐T and PTQDPP‐2FT, based on a newly developed quinoidal unit with thienoisatin as the termini and a thiophene‐flanked diketopyrrolopyrrole (ThDPP) unit as the quinoidal core. The electron‐rich thiophene rings in thienoisatin and the electron delocalization induced by thienoisatin resulted in polymers with high‐lying highest occupied molecular orbital, and the electron‐deficient nature of ThDPP unit and its quinoidal backbone endowed the polymers with low‐lying lowest unoccupied molecular orbitals. As a result, both polymers can be p‐type and n‐type doped. Because of its high mobility, doped PTQDPP‐2FT performed better in organic thermoelectric devices than the doped PTQDPP‐T. After being doped with FeCl3 and N‐DMBI, PTQDPP‐2FT showed p‐type and n‐type power factors of 278.2 and 2.37 µW m−1 K−2, respectively. These are the best for bipolar (p‐type and n‐type) performances that obtained by selective doping of a single polymer.

Nonpolymer Organic Solar Cells: Microscopic Phonon Control to Suppress Nonradiative Voltage Loss via Charge-Separated State.

Recent remarkable developments on nonfullerene solar cells have reached a photoelectric conversion efficiency (PCE) of 18% by tuning the band energy levels in small molecular acceptors. In this regard, understanding the impact of small donor molecules on nonpolymer solar cells is essential. Here, we systematically investigated mechanisms of solar cell performance using diketopyrrolopyrrole (DPP)-tetrabenzoporphyrin (BP) conjugates of C4-DPP-H2BP and C4-DPP-ZnBP, where C4 represents the butyl group substituted at the DPP unit as small p-type molecules, while an acceptor of [6,6]-phenyl-C61-buthylic acid methyl ester is employed. We clarified the microscopic origins of the photocarrier caused by phonon-assisted one-dimensional (1D) electron-hole dissociations at the donor-acceptor interface. Using a time-resolved electron paramagnetic resonance, we have characterized controlled charge-recombination by manipulating disorders in π-π donor stacking. This ensures carrier transport through stacking molecular conformations to suppress nonradiative voltage loss capturing specific interfacial radical pairs separated by 1.8 nm in bulk-heterojunction solar cells. We show that, while disordered lattice motions by the π-π stackings via zinc ligation are essential to enhance the entropy for charge dissociations at the interface, too much ordered crystallinity causes the backscattering phonon to reduce the open-circuit voltage by geminate charge-recombination.

Synergetic Effects of Random Copolymerization/Backbone Fluorination and Heterojunction of Terpolymer/g‐C3N4 Enhance Photocatalytic Hydrogen Evolution

In the field of photocatalytic hydrogen evolution, most polymer heterojunctions (PHJs) exhibit an unsatisfactory hydrogen evolution rate due to the decay of undissociated excitons, charge recombination, and weak light capture capacity. Herein, the design and synthesis of a series of D–A1–D–A2‐type random conjugated terpolymers (DIn, n = 1, 2, 3) are reported by copolymerizing fluorinated 2,2′‐bithiophene with different proportions of diketopyrrolopyrrole (DPP) and isoindigo (IID) for efficient vis‐light‐driven hydrogen evolution. Notably, the ternary copolymerization and fluorination strategy in the polymer backbone would enhance the intramolecular interactions and rebuild the extended π‐network over the polymeric heterojunction, which achieve broad and strong absorption ranging from 350 to 900 nm and a better effective photoexcitation separation, thus leading to a significantly increased hydrogen evolution reaction (HER) of 16.01 mmol h−1 g−1, via simply tuning the composition of DPP and IID units in the backbone of random terpolymers. The HER performance is almost 20 times higher than that of the typical g‐C3N4. This work offers a new strategy to develop efficient visible‐light‐driven photocatalysts via ternary copolymerization and backbone fluorination strategy of terpolymer/g‐C3N4 PHJs for broadband solar photon harvesting.

Uniform π‐Conjugated‐Co‐Oligomer‐Based Nanofibers of Controlled Length with Near‐Infrared Emission, Photodynamic and Photothermal Activities

Abstractπ‐Conjugated‐polymer‐based nanofibers (CPNFs) have attracted considerable interest in the community of nanomedicine owing to their high‐aspect‐ratio architecture and inherent photo‐imaging, photothermal, photodynamic, and photoacoustic properties. However, the preparation of uniform CPNFs of controlled length and composition with near‐infrared emission (NIR), photothermal and photodynamic activity remains in its infancy. A novel block copolymer consisting of a donor‐acceptor‐donor (D‐A‐D) π‐conjugated co‐oligomer with a diketopyrrolopyrrole (DPP) unit as electron‐deficient acceptor flanked by oligo(p‐ phenylene ethynylene) (OPE) as an electron‐rich donor and a poly(2‐vinylpyridine) (P2VP) block (OPE4‐DPP‐OPE4‐b‐P2VP44, the subscripts describe the extra and average number of repeat units for π‐conjugated OPE segment and P2VP block, respectively) is designed and synthesized. By using the self‐seeding approach of living crystallization‐drive self‐assembly (CDSA), uniform CPNFs containing a D‐A‐D OPE4‐DPP‐OPE4 core and a P2VP corona with tunable length from 31 to 611 nm are generated. The resulting CPNFs exhibit NIR emission with a peak at 837 nm. The CPNFs also can serve as a photosensitizer to efficiently produce single oxygen and show a photothermal effect upon 660 nm irradiation. To the author's best knowledge, it is the first report on the generation of uniform CPNFs of controlled length with NIR emission, and photodynamic and photothermal activities by living CDSA.

A Theoretical Design of Chiral Molecules through Conformational Lock towards Circularly Polarized Luminescence

Circularly polarized (CP) light has shown great potential in quantum computing, optical communications, and three-dimensional displays. It is still a challenge to produce high-efficiency and high-purity CP light. Herein, we proposed a strategy to design chiral organic small molecules for CP light generation. These kinds of chiral molecules are formed by achiral light-emitting groups and achiral alkyl chains through conformational lock, which indicates that chirality can also be introduced into achiral light-emitting groups through rational molecular design. The chirality of these molecules can be further tuned by changing the length of the alkyl chains connecting the diketopyrrolopyrrole unit. The chiroptical properties of these molecules are confirmed by calculated electronic circular dichroism and chiral emission spectra, and further confirmed in experiments. The strategy developed in this work will greatly enlarge the candidate library of chiral luminescent materials.

Side-chain engineering by thymine groups enables hydrogen bond in P-type donor-acceptor polymers with enhanced optoelectronic properties

Realizing ordered structures at the molecular level is a key approach to increase the charge mobility of organic semiconductors. However, the typical solution-based methods employed for the processing make the achievement of well-organized organic nanostructures difficult with the favored formation of disordered assemblies. To realize well-ordered thin films, one needs to design conjugated materials with the ability of self-assembling. In this work, two alternating donor-acceptor copolymers based on the carbazole and diketopyrrolopyrrole (DPP) units, namely P1 and P2, are successfully synthesized. Compared to P1, the polymer P2 contains an extra thymine group at the end of the alkyl chain, through which the hydrogen bonding (CO⋯NH) can be formed between the amide (NH) and carbonyl units (CO), as verified by the fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) study. The electrochemical analysis shows that the hydrogen bonding association influences the carbazole donor ability, resulting in a higher HOMO energy level of P2 compared to P1. In addition, the as-formed hydrogen bonds promote the assembling of the molecules into highly ordered structures by enabling strong aggregation as well as a narrow distance between adjacent molecules with long-range ordering packing and large nanocrystalline grains. As a result, the intermolecular charge transfer is enhanced. Consequently, the organic field-effect transistors (OFETs) constructed with P2 as the semiconductor layer present a p-type behavior with maximum hole mobility up to 1.32 cm2 V−1 s−1 upon annealing, which is almost 5 times higher than that of the pristine P2 (0.26 cm2 V−1 s−1), while the hole mobility of the annealed P1 is only 0.23 cm2 V−1 s−1. Our results indicate that the alkyl chain engineering, with the introduction of a thymine group into the donor units of the polymer, is responsible for the formation of hydrogen-bonded superstructures. This is a facile approach to enhance the optoelectronic properties of organic semiconductors.

(Invited) Metalation Effect on Diketopyrrolopyrrole-Tetrabenzoporphyrin Conjugate As p-Type Material in BHJ Organic Photovoltaics

Organic photovoltaics have attracted much attention for the next generation of photovoltaics. Tetrabenzoporphyrin (BP) is a p-type organic semiconductor characterized as the large, rigid p-framework, excellent stability, and good photoabsorption capability. Because of the low solubility, thermal precursor approach is necessary for the deposition of BP by solution process, where a soluble precursor (CP) of BP is spin-coated on the substrate, followed by annealing of CP film to make BP film by in-situ retro-Diels-Alder reaction of CP.[1,2] In 2017, we reported side-chain engineering for efficient photocurrent generation using a series of diketopyrrolopyrrole (DPP)–tetrabenzoporphyrin (BP) conjugates named Cn-DPP–BP (n = 4, 6, 8 or 10 depending on the length of n-alkyl groups on the DPP unit) as p-type materials in BHJ OPVs in combination with PC61BM as a n-type material by the thermal precursor approach.[3] The comparative study shows that the short-circuit current density largely depends on the length of alkyl substituents, ranging from 0.88 mA cm-2 with C10-DPP–BP to 15.2 mA cm-2 with C4-DPP–BP. C10-DPP–BP in the film is edge-on orientation dominant while that of C4-DPP–BP is face-on orientation dominant.Encouraged with the results, we synthesized a zinc complex of C4-DPP-CP (C4-DPP-ZnCP) as a soluble precursor of C4-DPP-ZnBP to investigate the effect of metalation of the porphyrin cavity for the BHJ OPV performance. BHJ OPV was prepared by thermal precursor approach: spin-coating of a mixed solution of the precursor, C4-DPP-ZnCP, and PC61BM, followed by annealing at 200 ºC to make a blend film of C4-DPP-ZnBP and PC61BM. Interestingly, the energy gap and ionization potential of C4-DPP-ZnBP film and C4-DPP-BP film are similar to each other, but the Jsc of C4-DPP-ZnBP is 1.5 times larger than that of C4-DPP-BP. We will discuss the relationship between film morphology and OPV performance by studying the blend film of C4-DPP-ZnBP/PC61BM by atomic force microscopy (AFM), X-ray diffraction (XRD) analysis and p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS).References H. Yamada, T. Okujima, N. Ono, Chem. Commun. 2008, 2957-2974. H. Yamada, D. Kuzuhara, M. Suzuki, H. Hayashi, N. Aratani, Bull. Chem. Soc. Jpn. 2020, 93, 1234-1267. K. Takahashi, D. Kumagai, N. Yamada, D. Kuzuhara, Y. Yamaguchi, N. Aratani, T. Koganezawa, S. Koshika, N. Yoshimoto, S. Masuo, M. Suzuki, K. Nakayama, H. Yamada, J. Mater. Chem. A 2017, 5, 14003-14011.

The Role of Long-Alkyl-Group Spacers in Glycolated Copolymers for High-Performance Organic Electrochemical Transistors.

Semiconducting polymers with oligoethylene glycol (OEG) sidechains have attracted strong research interest for organic electrochemical transistor (OECT) applications. However, key molecular design rules for high-performance OECTs via efficient mixed electronic/ionic charge transport are still unclear. In this work, new glycolated copolymers (gDPP-TTT and gDPP-TTVTT) with diketopyrrolopyrrole (DPP) acceptor and thiophene (T) and vinylene (V) thiophene-based donor units are synthesized and characterized for accumulation mode OECTs, where a long-alkyl-group (C12 ) attached to the DPP unit acts as a spacer distancing the OEG groups from the polymer backbone. gDPP-TTVTT shows the highest OECT transconductance (61.9 S cm-1 ) and high operational stability, compared to gDPP-TTT and their alkylated counterparts. Surprisingly, gDPP-TTVTT also shows high electronic charge mobility in a field-effect transistor, suggesting efficient ion injection/diffusion without hindering its efficient electronic charge transport. The elongated donor unit (TTVTT) facilitates hole polaron formation to be more localized to the donor unit, leading to faster and easier polaron formation with less impact on polymer structure during OECT operation, as opposed to the TTT unit. This is supported by molecular dynamics simulation. These simultaneously high electronic and ionic charge-transport properties are achieved due to the long-alkyl-group spacer in amphipathic sidechains, providing an important molecular design rule for glycolated copolymers.

Small molecules based on strongly electron-deficient aza-isatinylidene malononitrile for solution-processed n-type field-effect transistors

In this paper, three donor–acceptor (D/A) small molecules (M1, M2, and M3) based on aza-isatinylidene malononitrile (AIMN) and diketopyrrolopyrrole (DPP) containing different N-alkyl chains in AIMN unit were synthesized and characterized for application in solution-processable organic field-effect transistors (OFETs). The D/A small molecules with strongly electron-withdrawing AIMN and DPP units exhibited broad absorption spectra, low bandgaps, and deep lowest unoccupied molecular orbital energy levels (< – 4.0 eV). Consequently, OFET devices displayed unipolar electron transport characteristics with the highest electron mobilities of 0.26, 0.22, and 0.0079 cm2V–1s–1 for M1, M2, and M3, respectively. The small molecules with linear side chains showed much higher field-effect performances than that of branched side chains- based small molecule, due to the strong π–π stacking and appropriate morphology. This work indicated that the strongly electron-deficient AIMN should be a potential unit for constructing the n-type solution-processable small molecular semiconductors.

Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion.

Diketopyrrolopyrrole (DPP) is a pivotal functional group to tune the physicochemical properties of novel organic photoelectronic materials. Among multiple uses, DPP-thiophene derivatives forming a dimer through a vinyl linker were recently shown to quench the fluorescence observed in their isolated monomers. Here, we explain this fluorescence quenching using computational chemistry. The DPP-thiophene dimer has a low-lying doubly excited state that is not energetically accessible for the monomer. This state delays the fluorescence allowing internal conversion to occur first. We characterize the doubly excited state wavefunction by systematically changing the derivatives to tune the π-scaffold size and the acceptor and donor characters. The origin of this state's stabilization is related to the increase in the π-system and not to the charge-transfer features. This analysis delivers core conceptual information on the electronic properties of organic chromophores arranged symmetrically around a vinyl linker, opening new ways to control the balance between luminescence and internal conversion.