Pi-conjugated Materials Research Articles

Application of infrared and near-infrared photosensitive pi-conjugated materials in the diagnosis and rehabilitation of sports injuries in aerobics

According to a survey in 2021, around 12% of people were injured during the exercise, and they require the immediate healing process. Several tissue healing materials are incorporated into the sports rehabilitation process. However, the materials have a high rejection reaction rate, poor effect, and low healing speed, which affects aerobics rehabilitation training. The research difficulties are overcome by applying infrared and near-infrared photosensitive pi-conjugated materials to tissue healing procedures to maximize the result of sports rehabilitation. The research analysis discusses the conjugated materials composition and biocompatibility properties which helps to manage the skin healing drug release rate and durations. In addition, the pi-conjugated materials having a high Nearer-Infrared (NIR) observation rate between 600 nm to 1000nm then the materials are suitable for the photobiomodulation therapy wavelength. Then, NIR triggers the drug release from conjugated materials that are used to locate the injured area for treatment and rehabilitation process. Therefore, infrared and NIR-based conjugated materials effectively support injury rehabilitation and damaged tissue regeneration processes. The system efficiency is evaluated using various skin healing rates with different experiments and experimental groups.

On the Intermolecular Interactions in Thiophene-Cored Single-Stacking Junctions.

There have been attempts, both experimental and based on density-functional theory (DFT) modeling, at understanding the factors that govern the electronic conductance behavior of single-stacking junctions formed by pi-conjugated materials in nanogaps. Here, a reliable description of relevant stacked configurations of some thiophene-cored systems is provided by means of high-level quantum chemical approaches. The minimal structures of these configurations, which are found using the dispersion-corrected DFT approach, are employed in calculations that apply the coupled cluster method with singles, doubles and perturbative triples [CCSD(T)] and extrapolations to the complete basis set (CBS) limit in order to reliably quantify the strength of intermolecular binding, while their physical origin is investigated using the DFT-based symmetry-adapted perturbation theory (SAPT) of intermolecular interactions. In particular, for symmetrized S-Tn dimers (where "S" and "T" denote a thiomethyl-containing anchor group and a thiophene segment comprising "n" units, respectively), the CCSD(T)/CBS interaction energies are found to increase linearly with n ≤ 6, and significant conformational differences between the flanking 2-thiophene group in S-T1 and S-T2 are described by the CCSD(T)/CBS and SAPT/CBS computations. These results are put into the context of previous work on charge transport properties of S-Tn and other types of supramolecular junctions.

Mixed Ion-Carrier Diffusion in Poly(3-hexyl thiophene)/Perchlorate Electrochemical Systems

The electrochemical reduction and oxidation of pi-conjugated materials is a ubiquitous characterization tool involving the process of mixed ion-carrier transport. The kinetics of this process is im...

Highly Purified Materials for Sn-and Pb-Based Perovskite Solar Cells

Perovskite solar cells are promising cost-effective next generation printable photovoltaics. These solar cells have attracted the interest of many researchers. Thanks to tremendous effort of the researchers in this field, the power conversion efficiencies (PCEs) have been substantially increased in a short period, which is mainly due to improvements of the fabrication protocols for the perovskite layer as well as the development of new materials for buffer layers.Our approaches toward efficient lead and lead-free perovskite solar cells are as follows: Development of highly-purified perovskite precursor materialsDevelopment of solution process fabrication methods for the perovskite layerDevelopment of organic semiconductors for efficient charge-collection layers We have synthesized lead-halide and tin halide complexes as purified precursors for perovskite materials, which were later commercialized by TCI and are now widely used in this field as standard precursor materials. We also focus on the intermediates formed during the film-growth and have developed efficient fabrication methods based on the formation mechanism. We have designed and synthesized novel pi-conjugated materials designed to control frontier orbital energy levels, molecular aggregation properties, and the interface with the perovskite layer.In this talk, our recent progress on tin halide perovskite solar cells as well as lead halide perovskites will be introduced.

Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

The S1 (21Ag-) state is an optically dark state of natural and synthetic pi-conjugated materials that can play a critical role in optoelectronic processes such as, energy harvesting, photoprotection and singlet fission. Despite this widespread importance, direct experimental characterisations of the electronic structure of the S1 (21Ag-) wavefunction have remained scarce and uncertain, although advanced theory predicts it to have a rich multi-excitonic character. Here, studying an archetypal polymer, polydiacetylene, and carotenoids, we experimentally demonstrate that S1 (21Ag-) is a superposition state with strong contributions from spin-entangled pairs of triplet excitons (1(TT)). We further show that optical manipulation of the S1 (21Ag-) wavefunction using triplet absorption transitions allows selective projection of the 1(TT) component into a manifold of spatially separated triplet-pairs with lifetimes enhanced by up to one order of magnitude and whose yield is strongly dependent on the level of inter-chromophore coupling. Our results provide a unified picture of 21Ag-states in pi-conjugated materials and open new routes to exploit their dynamics in singlet fission, photobiology and for the generation of entangled (spin-1) particles for molecular quantum technologies.

Optical Projection and Spatial Separation of Spin Entangled Triplet-Pairs from the S <sub>1</sub> (2 <sup>1</sup>A <sub>g</sub> <sup>-</sup>) State of Pi-Conjugated Systems

The S1 (21Ag-) state is an optically dark state of natural and synthetic pi-conjugated materials that can play a critical role in optoelectronic processes such as, energy harvesting, photoprotection and singlet fission. Despite this widespread importance, direct experimental characterisations of the electronic structure of the S1 (21Ag-) wavefunction have remained scarce and uncertain, although advanced theory predicts it to have a rich multi-excitonic character. Here, studying an archetypal polymer, polydiacetylene, and carotenoids, we experimentally demonstrate that S1 (21Ag-) is a superposition state with strong contributions from spin-entangled pairs of triplet excitons (1(TT)). We further show that optical manipulation of the S1 (21Ag-) wavefunction using triplet absorption transitions allows selective projection of the 1(TT) component into a manifold of spatially separated triplet-pairs with lifetimes enhanced by up to one order of magnitude and whose yield is strongly dependent on the level of inter-chromophore coupling. Our results provide a unified picture of 21Ag- states in pi-conjugated materials and open new routes to exploit their dynamics in singlet fission, photobiology and for the generation of entangled (spin-1) particles for molecular quantum technologies.

Charge Transport Simulations in Conjugated Dendrimers

We present here a theoretical methodology that exploits quantum mechanical calculations, molecular mechanics calculations, and Monte Carlo simulations to predict the time-of-flight measurement mobilities in films of phenyl-cored conjugated thiophene dendrimers. Our aim is to reveal structure-property relationships in amorphous films of organic pi-conjugated materials. The simulations show that both hole and electron mobilities increase with the size of dendrimer, and that the former is larger than latter in all dendrimers. Internal reorganization energies are inversely correlated with the mobilities. Our simulations also indicate that dendrimers have small density of states for energetic disorder (<60 meV), and both hole and electron mobilities possess weak electric field dependence. We examine the influence of external reorganization energy as well as the possible trap sites on charge transport in these materials.

Supramolecular Ring Banded Prototype Liquid Crystalline Oligo(phenylenevinylene)

We report a new ring banded supramolecular structure in thermotropic liquid crystalline oligo(phenylenevinylene) (OPV) via a melt crystallization process. A series of structurally different OPV molecules were synthesized using tricyclodecanemethanol (TCD) as a bulky pendant unit to trace ring banded morphology. Among all, an OPV molecule with rigid bis-TCD units in the central core and flexible dodecyl chains at the outer phenyl rings (BTCD-BDD-OPV) was found to show ring banded morphologies, which is a first of its kind in pi-conjugated materials. BTCD-BDD-OPV experiences strong aromatic pi-pi interactions in both film and liquid crystalline (LC) frozen stage. The pi-induced aggregation leads to lamellar self-assembly of OPV-mesogens that subsequently undergo helical crystal growth, thereby producing dark and bright ring banded patterns. Variable temperature X-ray diffraction analysis revealed the existence of three peaks at 27.07, 13.97, and 8.90 A corresponding to 001, 002, and 003 fundamental layers, respectively, thus confirming the lamellar self-assembly of OPV-mesogens. Electron microscopic (SEM and TEM) analysis of the LC frozen sample showed images confirming helical microcrystalline assembly and providing direct evidence for the self-organization mechanism. Detailed photophysical experiments such as excitation, emission, and time-resolved fluorescence decay studies indicated that BTCD-BDD-OPV has very strong pi-pi interaction in both film and LC frozen stage, which was found to be main driving force for the formation of supra-ring structure. Upon illumination with light, the OPV chromophores in the LC phase were excited and the color of the samples turned into luminescent green ring bands.

Highly Disordered Polymer Field Effect Transistors: N-Alkyl Dithieno[3,2-b:2′,3′-d]pyrrole-Based Copolymers with Surprisingly High Charge Carrier Mobilities

A series of novel electroactive and photoactive conjugated copolymers based on N-alkyl dithieno[3,2-b:2',3'-d]pyrroles (DTP) and thiophene (TH) units (DTP-co-THs) were synthesized using a Stille coupling reaction and exhibited molecular weights of 1.6 x 10(4) to 5.0 x 10(4) g/mol. The incorporation of soluble substituted thiophenes and planar DTP units resulted in low band gap, highly conductive polymers. DTP-co-THs exhibited excellent solubility in common organic solvents and formed high-quality films. Optical characterization revealed that the band gaps of DTP-co-THs were between 1.74 and 2.00 eV, lower than regioregular poly(3-alkylthiophenes). Electrochemical characterization showed that the HOMO energy levels of DTP-co-THs are between -4.68 and -4.96 eV. When doped, DTP-co-THs exhibited high conductivities up to 230 S/cm with excellent stability. The different thiophene substituent patterns' effect on the polymers' optical and electronic properties was then examined by density functional theory computations. The microstructure and surface morphologies of poly(2,6-(4-dodecyl-4H-bisthieno[3,2-b:2',3'-d]pyrrole)-random-2,5-(3-dodecylthiophene)) (P4) and poly(2-(4,4'-didodecyl-2,2'-bithiophen-5-yl)-4-octyl-4H-bisthieno[3,2-b:2',3'-d]pyrrole) (P6) thin films were studied by X-ray diffraction and atomic force microscopy. As-cast P4 and P6 thin films exhibited poorly defined, randomly ordered lamellar structure that improved significantly after thermal annealing. Field effect transistor devices fabricated from P4 and P6 showed typical p-channel transistor behavior. Interestingly, the mobilities of as-cast, less ordered samples were much higher than those observed after annealing. The highest values of maximum and average mobilities were observed for the polymer P6 as-cast (0.21 and 0.13 cm(2) V(-1) s(-1), respectively). One of our goals was to test the idea that high mobility and excellent electrical and structural reproducibility could perhaps be achieved by the creation of amorphous pi-conjugated materials that could possess long arrange pi connectivity on the microscopic scale. The results of these studies strongly suggest that the presence of highly ordered microcrystalline structures in thin films of organic semiconductors is not necessary for excellent performance of organic transistors.

Bipolaron Mechanism for Organic Magnetoresistance

We present a mechanism for the recently discovered magnetoresistance in disordered pi-conjugated materials, based on hopping of polarons and bipolaron formation, in the presence of the random hyperfine fields of the hydrogen nuclei and an external magnetic field. Within a simple model we describe the magnetic field dependence of the bipolaron density. Monte Carlo simulations including on-site and longer-range Coulomb repulsion show how this leads to positive and negative magnetoresistance. Depending on the branching ratio between bipolaron formation or dissociation and hopping rates, two different line shapes in excellent agreement with experiment are obtained.

Impact of ring torsion on the intrachain mobility in conjugated polymers

In this thesis we explore in particular the dynamics of a special type of quasi-particle in pi-conjugated materials termed polaron, the origin of which is intimately related to the strong interactions between the electronic and the vibrational degrees of freedom within these systems. In order to conduct such studies with the particular focus of each appended paper, we simultaneously solve the time-dependent Schrodinger equation and the lattice equation of motion with a three-dimensional extension of the famous Su-Schrieffer-Heeger (SSH) model Hamiltonian. In particular, we demonstrate in Paper I the applicability of the method to model transport dynamics in molecular crystals in a region were neither band theory nor perturbative treatments such as the Holstein model and extended Marcus theory apply. In Paper II we expand the model Hamiltonian to treat the revolution of phenylene rings around the sigma-bonds and demonstrate the great impact of stochastic ring torsion on the intra-chain mobility in conjugated polymers using poly[phenylene vinylene] (PPV) as a model system. Finally, in Paper III we go beyond the original purpose of the methodology and utilize its great flexibility to study radiationless relaxations of hot excitons.

Charge Hopping in Organic Semiconductors: Influence of Molecular Parameters on Macroscopic Mobilities in Model One-Dimensional Stacks

We present a Monte Carlo approach to estimate how molecular parameters impact hopping rates and charge mobilities in organic pi-conjugated materials. Our goal is to help in establishing structure-properties relationships. As a first step, our approach is illustrated by considering a model system made of a one-dimensional array of pentacene molecules; we describe the variations of the electron-transfer rates and of the resulting charge mobilities as a function of electric field and of the presence of molecular disorder and traps. The results highlight that there is no direct relationship between the degree of spatial overlap among adjacent molecules and charge mobility.

The effects of supramolecular assembly on exciton decay rates in organic semiconductors

We present time-resolved photoluminescence measurements on two series of oligo-p-phenylenevinylene (OPV) materials that are functionalized with quadruple hydrogen-bonding groups. These form supramolecular assemblies with thermotropic reversibility. The morphology of the assemblies depends on the way that the oligomers are functionalized; monofunctionalized OPVs (MOPVs) form chiral, helical stacks while bifunctionalized OPVs (BOPVs) form less organized structures. These are therefore model systems to investigate the effects of supramolecular assembly, the effects of morphology, and the dependence of oligomer length on the radiative and nonradiative rates of pi-conjugated materials. The purpose of this work is to use MOPV and BOPV derivatives as model systems to study the effect of intermolecular interactions on the molecular photophysics by comparing optical properties in the dissolved phase and the supramolecular assemblies. A simple photophysical analysis allows us to extract the intrinsic radiative and nonradiative decay rates and to unravel the consequences of interchromophore coupling with unprecedented detail. We find that interchromophore coupling strongly reduces both radiative and intrinsic nonradiative rates and that the effect is more pronounced in short oligomers.

From Model Compounds to Extended π‐Conjugated Systems: Synthesis and Properties of Dithieno[3,2‐b:2′,3′‐d]phospholes

To explore their suitability for applications in molecular optoelectronics and as sensory materials, novel dithieno[3,2-b:2',3'-d]phospholes have been synthesized and their reactivity and properties investigated. An efficient two-step synthesis allowed for a modular assembly of differently functionalized compounds. The dithieno[3,2-b:2',3'-d]phosphole system exhibits extraordinary optoelectronic properties with respect to wavelength, intensity, and tunability. Owing to the nucleophilic nature of the central phosphorus atom, its significant electronic influence on the conjugated pi system can be altered selectively by chemically facile modifications such as oxidation or complexation with Lewis acids or transition metals. All the dithienophosphole species presented show very strong blue photoluminescence with excellent quantum yield efficiencies supporting their potential utility as blue-light emitting components in organic light emitting diodes (OLEDs). Furthermore, depending on the electronic nature of the phosphorus center, the materials exhibit distinctive optoelectronic properties suggesting that the dithieno[3,2-b:2',3'-d]phosphole system may be useful as sensory material. Theoretical calculations, including time-dependent DFT methods, revealed the excellent predictability of the structures and optoelectronic properties of the functionalized dithienophospholes allowing the design of future dithieno[3,2-b:2',3'-d]phosphole-based materials to be "stream-lined". By using tin-functionalized dithienophosphole monomers, a strategy, which involves Stille coupling, towards extended pi-conjugated materials with significantly redshifted optoelectronic properties is also presented.

A Facile Synthesis and Properties of Multicarbazole Molecules Containing Multiple Vinylene Bridges

Multibranched pi-conjugated materials and hyperbranched polymers have received considerable interest in both academic research and industrial applications because of their unusual molecular structures and properties. In this communication, we provide an efficient approach to synthesize two novel pi-conjugated multibranch compounds, which have good solubility and are nanosize (about 5 nm). The double bonds of the multibranch compounds are synthesized using solvent-free Wittig-Horner-Emmons reactions. The reaction conditions are simple and mild. Their optical properties are discussed too.

Symmetrical Electron‐Deficient Materials Incorporating Azaheterocycles.

To investigate the potential of di- and tri-azaheterocycles as building blocks for pi-conjugated materials with high electron affinity, linear oligomers incorporating pyrazine and a C(3)-symmetric discotic molecule based on triazine were synthesized. The tridodecyloxyphenyl end-capped ethynylene pyrazinylene oligomers showed remarkable solvatochroism in absorption and emission in solution. The oligomers containing one and two pyrazine rings displayed liquid crystallinity in the solid state. The largest ethynylene pyrazinylene oligomer containing three pyrazine rings had the lowest first reduction potential at -1.08 V. The triazine-derived discotic molecule exhibited UV/Vis and fluorescence behavior comparable to that of the linear oligomers and featured a first reduction potential at -1.49 V, somewhat lower than expected.

Symmetrical electron-deficient materials incorporating azaheterocycles.

To investigate the potential of di- and tri-azaheterocycles as building blocks for pi-conjugated materials with high electron affinity, linear oligomers incorporating pyrazine and a C(3)-symmetric discotic molecule based on triazine were synthesized. The tridodecyloxyphenyl end-capped ethynylene pyrazinylene oligomers showed remarkable solvatochroism in absorption and emission in solution. The oligomers containing one and two pyrazine rings displayed liquid crystallinity in the solid state. The largest ethynylene pyrazinylene oligomer containing three pyrazine rings had the lowest first reduction potential at -1.08 V. The triazine-derived discotic molecule exhibited UV/Vis and fluorescence behavior comparable to that of the linear oligomers and featured a first reduction potential at -1.49 V, somewhat lower than expected.

SuMBE: Growth by Seeded Supersonic Beams of Organic Materials for Optoelectronic Devices

We have shown that thin film growth of pi-conjugated materials by seeded supersonic molecular beams (SuMBE) is an effective approach to control structure and morphology. These are key features to improve control on energy and charge transport properties and hence for the realization of improved devices including optolectronic applications. Recent results on phthalocyanines, thiophene oligomers and acenes will be discussed showing that control on the precursors, in terms of energy and momentum in particular, is of paramount importance in controlling the final properties of the films including the optical response as well as interfaces. Films showing optical properties comparable to those of the corresponding single crystals and with a controlled morphology have been produced by &#x201C;tuning&#x201D; the initial parameters in the beam. The initial kinetic energy, easily varied in the range from a fraction of eV up to tens of eV by changing the seeding of the molecules into an inert carrier gas (i.e. He, Ar, etc.), is shown to be a key parameter. Even the defect type and density as well as the polymorphism can be controlled by this method. In a SuMBE co-deposition scheme we have developed solar cells based on phtalocyanines and fullerenes the performance of which could be optimized by controlling the SuMBE deposition parameters. An outlook of the possible developments will be discussed in view of a new generation of devices.

Decoupling optical and potentiometric band gaps in pi-conjugated materials.

Syntheses, optical spectroscopy, potentiometric studies, and electronic structural calculations are reported for two classes of conjugated (porphinato)metal oligomers that feature a meso-to-meso ethyne-bridged linkage topology. One set of these systems, bis[(5,5'-10,20-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]ethyne (DD), 5,15-bis[[5'-10',20'-bis[3,5-di(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]ethynyl]-10,20-bis[3,5-di(9-methoxy-1,4,7-trioxanonyl)phenyl]porphinato)zinc(II) (DDD), and 5,15-bis[[15' '-(5'-10',20'-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]-[(5' '-10' ',20' '-bis[3,5-di(9-methoxy-1,4,7-trioxanonyl)phenyl]porphinato)zinc(II)]ethyne]ethynyl]-10,20-bis[3,5-di(9-methoxy-1,4,7-trioxanonyl)phenyl]porphinato)zinc(II) (DDDDD), constitute highly soluble analogues of previously studied examples of this structural motif having simple 10,20-diaryl substituents, while a corresponding set of conjugated oligomers, [(5-10,20-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]-[(5'-15'-ethynyl-10',20'-bis[10,20-bis(heptafluoropropyl)porphinato)zinc(II)]ethyne (DA), 5,15-bis[[5'-10',20'-bis[3,5-di(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]ethynyl]-10,20-bis(heptafluoropropyl)porphinato]zinc(II) (DAD), and 5,15-bis[[15' '-(5'-10',20'-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]-[(5' '-(10' ',20' '-bis(heptafluoropropyl)porphinato)zinc(II)]ethyne]ethynyl]-10,20-bis[3,5-di(9-methoxy-1,4,7-trioxanonyl)phenyl]porphinato)zinc(II) (DADAD), features alternating electron-rich and electron-poor (porphinato)zinc(II) units. Electrooptic and computational data for these species demonstrate that it is possible to engineer conjugated oligomeric structures that possess highly delocalized singlet (S1) excited states yet manifest apparent one-electron oxidation and reduction potentials (E1/20/+ and E1/2-/0 values) that are essentially invariant with respect to those elucidated for their constituent monomeric precursors.