Π-conjugated Organic Molecules Research Articles

Synthesis, structure and photophysical properties of truxene and truxene-triindole compounds

Multi-branched π-conjugated organic molecules, due to their fascinating structures and unique optical properties, exhibit potential applications in optoelectronics. Herein, series of 4-N,N-diphenylaminostyryl substituted multi-branched truxene compounds (namely TN1, TN2 and TN3) and a truxene-triindole compound (namely N3T3) were synthesized. These compounds are characterized by effective π-extension and remarkably enhanced two-photon absorption (TPA) compared to their less π-conjugated analogues. For truxene compounds, the more the number of the branch, the large the TPA efficiency, and the C3-symmetric three-branched TN3 exhibit the largest TPA. The aromatic triindole unit proves to be a better two-photon fluorophore compared with truxene. The results conclude that the influence of π-conjugation, molecular planarity and intramolecular charge-transfer (ICT) to TPA is far more pronounced than to linear optical properties.

Cucurbit[8]uril-modulated discrete pyrene dimers fluorescent sensor for nitroaromatic compounds and latent fingerprints visualization

As a promising class of luminescent materials, π-conjugated organic aromatic molecules are usually subject to aggregation-caused quenching (ACQ) effect, which limits their wide application. Currently, obtaining structurally visualized solid luminescent materials of polycyclic aromatic hydrocarbons (PAHs) without complex synthetic purification steps remains a challenging topic. Herein, we focus on the supramolecular assembly strategy to constructed a solid fluorescent material (HPTS@Q[8]@Rb+) by co-assembling cucurbit[8]uril (Q[8]) with 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and rubidium ions based on the coordination and outer surface interactions of Q[8]. HPTS@Q[8]@Rb+ exhibited good fluorescence properties with quantum yields of 2.28 % and 73.15 % in solid state and aqueous suspensions, respectively, providing a good sensing platform for nitroaromatic compounds (NACs), especially for 2,4,6-trinitrophenol (PA) and 4-nitroaniline (4-NA) with remarkable quenching constants (KSV=4.06×104 M−1 for PA and KSV=2.95×104 M−1 for 4-NA) in working range of 0–3.33×104 M and 0–5.0×104 M, respectively. Moreover, a fluorescent fingerprint powder was prepared by combining montmorillonite (MMT) for high-resolution visualization of latent fingerprints (LFPs) without substrate limitation. This study demonstrates the synthesis of Q[n]-based fluorescent material, the anion-rich aromatic compounds can be used as potential moieties for assembly with Q[n], providing a facile and promising approach to develop PAHs-based luminescent materials. This supramolecular self-assembly strategy provides a fundamental design principle for the creation of diverse functional crystalline solid materials.

On the importance of varying device thickness and temperature on the outcome of space-charge-limited current measurements

Space-charge-limited current (SCLC) measurements are commonly employed to characterize charge-transport properties of semiconductors used in next-generation thin-film optoelectronics, such as organic π-conjugated small molecules and polymers, and metal-halide perovskites. Despite the wide-spread adoption of the method, there is no community-wide consensus around how SCLC measurements should be performed, nor how the data should be analyzed and reported. While it is common to report device characteristics by employing a simplistic analytical model for fitting a single J-V curve obtained from a solitary device at room temperature—sometimes in a very select voltage range—expectedly, such an approach will often not give an accurate picture of the underlying physics. On that account, we here aim to highlight the importance of reporting values extracted from not just a solitary single-carrier device measured at room temperature, but from devices with different thicknesses measured at varying device temperature. We also highlight how the choice of device thickness is especially critical in determining what device and material characteristics can be extracted from SCLC measurements, and how this choice can greatly affect the conclusions drawn about the probed semiconducting material. While other factors could affect the outcome of an SCLC measurement and the subsequent analysis, we hope that the topics covered in this article will result in overall improved charge-transport characterization of thin-film semiconductors and initiate a broader discussion into SCLC metrology at large.

Theoretical Insights into the Structural and Optical Properties of D-π-A-based Cyanostilbene Systems of α and β Variants.

The π-conjugated organic molecules containing cyanostilbene motifs have been extensively investigated due to their great potential applications in several optoelectronic and biological fields. Developing efficient molecules in this respect requires strategic structural engineering and a deep understanding of the structure-property relationship at the molecular level. In this context, understanding the impact of positional isomerism in cyanostilbene systems is a fundamental aspect of designing desired materials with improved photophysical properties. Herein, we designed ten donor-π-acceptor (D-π-A) type cyanostilbene derivatives (P1 - P10) with different π linkers and compared their structural and optoelectronic properties arising from the positional variations of the -CN group (α and β- variations) through the utilization of density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The topological analyses of the electron density are used to explain the relatively high stability of α isomer compared to that of β. Frontier molecular orbital analysis reveals that 17 molecules tend to show a reduced highest occupied molecular orbital-lowest unoccupied molecular orbital gap, and most of them showed a greater nonlinear optical (NLO) character compared to the parent molecule. TDDFT calculations indicate that β isomers show higher absorption maxima compared to their α counterparts. Among all the scrutinized molecules, the absorption maximum extended up to 602 nm for P9 and it possesses the highest first-order hyperpolarizability. This study sheds light on positional isomers and their reactivity, absorption spectra, and NLO properties of D-π-A type architecture that can be suitably tuned by appropriating the π-bridge for practical applications.

Self-Assembly of Organic Semiconductors on Strained Graphene under Strain-Induced Pseudo-Electric Fields.

Graphene is used as a growth template for van der Waals epitaxy of organic semiconductor (OSC) thin films. During the synthesis and transfer of chemical-vapor-deposited graphene on a target substrate, local inhomogeneities in the graphene-in particular, a nonuniform strain field in the graphene template-can easily form, causing poor morphology and crystallinity of the OSC thin films. Moreover, a strain field in graphene introduces a pseudo-electric field in the graphene. Here, the study investigates how the strain and strain-induced pseudo-electric field of a graphene template affect the self-assembly of π-conjugated organic molecules on it. Periodically strained graphene templates are fabricated by transferring graphene onto an array of nanospheres and then analyzed the growth and nucleation behavior of C60 thin films on the strained graphene templates. Both experiments and a numerical simulation demonstrated that strained graphene reduced the desorption energy between the graphene and the C60 molecules and thereby suppressed both nucleation and growth of the C60. A mechanism is proposed in which the strain-induced pseudo-electric field in graphene modulates the binding energy of organic molecules on the graphene.

2D Conjugated Metal-Organic Frameworks: Defined Synthesis and Tailor-Made Functions.

Conspectus2D conjugated metal-organic frameworks (2D -MOFs) have emerged as a class of graphene-like materials with fully π-conjugated aromatic structures. Their unique structural characteristics provide abundant physiochemical features, including regular nanochannels, high electrical conductivity, and customizable band gaps. Recent intensive research has significantly advanced this field, yet the exploration of 2D c-MOFs with enhanced features is limited by the availability of organic linkages and topologies. Designing novel ligands is essential for the construction of new 2D c-MOFs with high crystallinity, excellent conductivity, and tailor-made functions.In this Account, we summarize our recent contributions in fine-tuning the topology of 2D c-MOFs through precise ligand design, thereby giving them fantastic structures and tailor-made functions. First, we propose the concept of replacing planar ligands by nonplanar ligands on conductive MOF skeletons. The incorporation of nonplanar ligands improves the solubility of large π-conjugated organic molecules without interfering with the interlayer π-stacking. Our investigation discovered that conjugate polycyclic aromatics-based ligands can be synthesized through in situ Scholl reactions by means of oxidative cyclodehydrogenation of a nonplanar precursor ligand during the solvothermal synthesis process. Hence, fully conjugated 2D c-MOFs can be directly synthesized from nonplanar organic ligands, simplifying and diversifying the preparation of 2D c-MOFs. Accordingly, the design flexibility of the ligands expands the topological structures and pore types. By controlling the synthesis conditions, we can successfully induce either a rhombus or a kagome topology from a nonplanar D2 symmetric ligand. Moreover, by employing a ligand engineering strategy, we incrementally increase the number of coordination functional groups on a twisted hexabenzocoronene core, resulting in the formation of three distinct symmetric hydroxyl ligands. These ligands elicit diverse target topologies and pore sizes, resulting in variances in the coordination node density on the skeletons. This, in turn, leads to differences in electron transfer abilities, ultimately causing variations in the electrical conductivity and mobility. In addition, we employ a straightforward coupling method to incorporate redox components, such as salphen and pyrazine, into nonplanar ligands, facilitating the synthesis of 2D c-MOFs with highly active centers. This strategy confers upon the resulting frameworks substantial capacity for catalysis and energy storage, offering a good platform for elucidating the structure-property relationships at the molecular level. Moreover, the well-defined synthesis of 2D c-MOFs imparts them with specific properties, particularly in the fields of electrical, electrochemical, and spintronic applications. At the end, the primary challenges facing 2D c-MOFs in achieving tailor functions and their practical applications are proposed. This account is expected to evoke new inspirations and innovative research in the field of 2D c-MOFs, especially in emerging interdisciplinary research areas.

P-type π-conjugated BTPDS-8 organic molecule for broadband hybrid photodetector with organic/inorganic heterostructure

A novel p-type π-conjugated organic small molecule 3,7-bis(4-([2,2′:6′,2''-terpyridin]−4′-yl)phenyl)− 5H-dibenzo[a,d][7]annulen-5-one (named as BTPDS-8) in which terpyridinyl units are linked to the dibenzosuberenone backbone by a phenyl bridge was successfully synthesized in four reaction steps. The synthesized organic material BTPDS-8 was fully characterized using 1H NMR, 13C NMR, IR, and HRMS spectroscopy techniques. Then, eleven BTPDS-8/Si heterojunctions were fabricated having non-linear current-voltage characteristics. Among these devices, the one with the highest rectification ratio (with 8.43 ×105) was analyzed in detail under UV and IR light as well as different intensities of visible light. Experimental results showed that the device has good photoresponse performance under any light source in addition to self-driven mode characteristics. It was observed that the saturation current and barrier height increased, and the ideality factor decreased, depending on the light intensity under visible light. Photocurrent, on/off ratio, responsivity, detectivity and NPDR were calculated from the optical measurements. The broad spectrum photoresponse of the BTPDS-8/Si heterojunction from UV to IR demonstrated that the device has the potential to be used as a broadband photodetector. The best performance was obtained under 850 nm IR light. The detectivity values under IR light were 1.22 × 1010 Jones and 7.53 × 109 Jones for V= 0.0 volts (self-driven mode) and V= −2.0 volts, respectively.

Beyond Planar Structure: Curved π-Conjugated Molecules for High-Performing and Stable Perovskite Solar Cells.

Perovskite solar cell (PSC) shows a great potential to become the next-generation photovoltaic technology, which has stimulated researchers to engineer materials and to innovate device architectures for promoting device performance and stability. As the power conversion efficiency (PCE) keeps advancing, the importance of exploring multifunctional materials for the PSCs has been increasingly recognized. Considerable attention has been directed to the design and synthesis of novel organic π-conjugated molecules, particularly the emerging curved ones, which can perform various unmatched functions for PSCs. In this review, the characteristics of three representative such curved π-conjugated molecules (fullerene, corannulene and helicene) and the recent progress concerning the application of these molecules in state-of-the-art PSCs are summarized and discussed holistically. With this discussion, we hope to provide a fresh perspective on the structure-property relation of these unique materials toward high-performance and high-stability PSCs.

Kinetic and Thermodynamic Control of Supramolecular Aggregation of Near Infrared Pyrrolopyrrole Cyanine Fluorophores Confined in Colloidal Nanoparticles.

Control of the intermolecular aggregation of organic π-conjugated molecules as chromophores is crucial for tuning their physical properties such as light absorption/emission, and energy and charge transfer. Lots of advances have been achieved in control of intermolecular aggregation of organic chromophores in solid states where an indefinitely large number of molecules are involved. However, much less understanding has been gained at a mesoscale of aggregates formed by well-defined organization of a deterministic number of chromophores, which has been realized in natural photosynthetic systems but still remains rare in manmade materials. Here, we report both the kinetic and the thermodynamic control of the supramolecular aggregation of a near-infrared cyanine dye, PPcy, and its derivatives confined in colloidal nanoparticles stabilized by surfactants in aqueous media. Our results demonstrate that both the aggregation number, the aggregation state and the optical properties of the PPcy chromophores are controllable through optimization of the alkyl and polymer chains tethered from PPcy, the effective concentration of the chromophore inside each particle, and the surfactants utilized to stabilize the colloids in water.

“All-organic” electrode materials toward high-performing rigid to flexible supercapacitor devices

Perylene diimide-2-amino benzimidazole, a donor–acceptor π-conjugated organic molecule, is utilized in fabricating rigid to flexible hybrid symmetric supercapacitor devices which exhibit nearly 96% retention of capacitance even after 2000 cycles.

Narcissistic self-sorting in Zn(II) porphyrin derived semiconducting nanostructures.

The narcissistic self-sorted phenomenon is explicitly attributed to the structural similarities in organic molecules. Although such relevant materials are rarely explored, self-sorted structures from macrocyclic π-conjugated-based p- and n-type organic semiconductors facilitate the increase of exciton dissociation and charge separation in bulk heterojunction solar cells. Herein, we report two extended π-conjugated derivatives consisting of zinc-porphyrin-linked benzothiadiazole acting as an acceptor (PB) and anthracene as a donor (PA). Despite having the same porphyrin π-conjugated core in PA and PB, variations in donor and acceptor moieties make the molecular packing form one-dimensional (1D) self-assembled nanofibers via H- and J-type aggregates. Interestingly, a dissimilar aggregate of PA and PB exists as a mixture (PA + PB), promoting narcissistic self-sorted structures. Electrochemical impedance investigation reveals that the electronic characteristics of self-sorting assemblies are influenced by the difference in electrostatic potentials for PA and PB, resulting in a transitional electrical conductivity of 0.14 S cm-1. Therefore, the design of such materials for the fabrication of effective photovoltaics is promoted by these extraordinary self-sorted behaviors in comparable organic π-conjugated molecules.

Effects of solvents on structure and energy of 6-amino-2-mercapto-3H-pyrimidin-4-one: A computational study

6-amino-2-mercapto-3H-pyrimidin-4-one (AMP) is a π-conjugated organic molecule extensively used as a semiconductor in many optoelectronic devices. The computational hybrid meta-generalized gradient Minnesota M06-2x, ωB97XD, and B3LYP functionals in conjunction with the correlation consistent polarized valence triplet zeta (cc-pVTZ) basis set and the moderate composite CBS-QB3 procedure were used with the aid of the Gaussian 09 program and the kinetic and statistical thermodynamical package (KiSThelP) in the temperature range 250–400 K to investigate the behavior of AMP in the gas phase, and in different polar (water, ethanol), and non-polar (dimethyl sulfoxide (DMSO), acetone)) solvents. Non-linear optical (NLO) characteristics and quantum chemical parameters were examined. Natural bond orbital analysis (NBO) was used to characterize the charge transfer of the electron density in the investigated compounds. The quality of the methods used was inspected and compared to give accurate results. The stability of AMP can be returned to the hyper conjugative interactions that leading to its nonlinear optical activity. Also, the charge delocalization was analyzed using natural bond orbital technique. The molecular electrostatic potential surfaces (MEPS) plots have been generated. The rate coefficients of tautomerization processes (kuni, in s−1) were calculated from the transition state theory (TST) and unimolecular Rice-Ramsperger-Kassel-Marcus (RRKM) methods. The results indicate comparable chemical rates obtained from TST and RRKM. In addition, positive temperature dependencies were located for all channels and a high dominance of transferring H-atom from the external N-atom to the S-atom (R3 reaction) during the applied temperature range which can return to its lower activation energy. This study is the first stone in studying AMP under different conditions such as the atmosphere, combustion conditions and as a nano catalyst.

Polarity-Induced Morphological Transformation with Tunable Optical Output of Terpyridine-Phenanthro[9,10-d]imidazole-Based Ligand and Its Zn(II) Complexes with I-V Characteristics.

Self-assembled nanostructures obtained from various functional π-conjugated organic molecules have been able to draw substantial interest due to their inherent optical properties, which are imperative for developing optoelectronic devices, multiple-color-emitting devices with color-tunable displays, and optical sensors. These π-conjugated molecules have proven their potential employment in various organic electronic applications. Therefore, the stimuli-responsive fabrication of these π-conjugated systems into a well-ordered assembly is extremely crucial to tuning their inherent optical properties for improved performance in organic electronic applications. To this end, herein, we have designed and synthesized a functional π-conjugated molecule (TP) having phenanthro[9,10-d]imidazole with terpyridine substitution at the 2 position and its corresponding metal complexes (TPZn and (TP)2Zn). By varying the polarity of the self-assembly medium, TP, TPZn, and (TP)2Zn are fabricated into well-ordered superstructures with morphological individualities. However, this medium polarity-induced self-assembly can tune the inherent optical properties of TP, TPZn, and (TP)2Zn and generate multiple fluorescence colors. Particularly, this property makes them useful for organic electronic applications, which require adjustable luminescence output. More importantly, in 10% aqueous-THF medium, TPZn exhibited H-type aggregation-induced white light emission and behaved as a single-component white light emitter. The experimentally obtained results of the solvent polarity-induced variation in optical properties as well as self-assembly patterns were further confirmed by theoretical investigation using density functional theory calculations. Furthermore, we investigated the I-V characteristics, both vertical and horizontal, using ITO and glass surfaces coated with TP, TPZn, and (TP)2Zn, respectively, and displayed maximum current density for the TPZn-coated surface with the order of measured current density TPZn > TP > (TP)2Zn. This observed order of current density measurements was also supported by a direct band gap calculation associated with the frontier molecular orbitals using the Tauc plot. Hence, solvent polarity-induced self-assembly behavior with adjustable luminescence output and superior I-V characteristics of TPZn make it an exceptional candidate for organic electronic applications and electronic device fabrication.

Molecular Engineering for Enhanced Thermoelectric Performance of Single-Walled Carbon Nanotubes/π-Conjugated Organic Small Molecule Hybrids.

Hybridizing single-walled carbon nanotubes (SWCNTs) with π-conjugated organic small molecules (π-OSMs) offers a promising approach for producing high-performance thermoelectric (TE) materials through the facile optimization of the molecular geometry and energy levels of π-OSMs. Designing a twisted molecular structure for the π-OSM with the highest occupied molecular orbital energy level comparable to the valence band of SWCNTs enables effective energy filtering between the two materials. The SWCNTs/twisted π-OSM hybrid exhibits a high Seebeck coefficient of 110.4 ± 2.6 µV K-1 , leading to a significantly improved power factor of 2,136 µW m-1 K-2 , which is 2.6 times higher than that of SWCNTs. Moreover, a maximum figure of merit over 0.13 at room temperature is achieved via the efficient TE transport of the SWCNTs/twisted π-OSM hybrid. The study highlights the promising potential of optimizing molecular engineering of π-OSMs for hybridization with SWCNTs to create next-generation, efficient TE materials.

Synthesis, characterization and computational study of the conjugated thiol-systems for self-assembled monolayers on gold electrode

In the present work, we examine the synthesis and characterization of the Π-conjugated organic molecules applied to immobilize the laccase enzyme on gold electrode surfaces. The density functional theory (DFT) and time-dependent (TD-DFT) were performed to compute the optoelectronic properties. The interactions between the ligand (conjugated thiol system) and the receptor (laccase enzyme) were investigated using docking simulations. The Π-conjugated systems were prepared by the Horner-Wadsworth-Emmons reaction. These conjugated organic molecules were further used to design a new generation of nanostructured bioelectrodes that allow the electrical connection of a laccase enzyme with the gold metallic surface. Direct electron transfer (DET) between the enzyme (laccase) and the gold electrode was achieved in a potentially straightforward manner. This modified cathode could be implemented in new biosensors to assess the concentration of particular analytes, such as the effective detection of O2 for healthcare monitoring and disease diagnosis. It could also be employed to develop promising biofuel cells.

Synthesis and Photophysical Properties of Carbazole-Functionalized Diazaphosphepines via Sequent P-N Chemistry.

Chemical structure tunability of organic π-conjugated molecules (OCMs) is highly appealing for fine-tuning the optoelectronic properties. Herein, we report a new series of carbazole-functionalized diazaphosphepines (DPP-CBZs) via one-pot phosphorus-nitrogen (P-N) chemistry. The one-pot synthesis harnessed the mild and selective P-N chemistry that successively installed carbazole moieties and seven-membered heterocycles at one P-center. Single-crystal structure studies revealed the tweezer-like structures for 1PO, 2PO, and 3PO that maintained the intramolecular donor-acceptor interactions between [d]-aryl moieties and carbazole. DPP-CBZs exhibited a more twisted central-diazaphosphepine ring compared with the reference molecules (1-3MO without carbazole group). DPP-CBZs with strong electron-accepting [d]-Ars generally showed lower photoluminescence quantum yields (PLQYs) than those of the reference molecules, which is probably due to the intramolecular charge transfer (ICT) from electron-donating carbazole to electron-withdrawing [d]-Ars. Upon the oxidation of the P-centers, PLQYs of DPP-CBZs increased. Furthermore, photophysical studies and theoretical studies suggested that the carbazole group had a strong impact on the structures of DPP-CBZs. As a proof of concept, we showed that grinding the mixture of 1PO as the electron-donating tweezer and benzene-1,2,4,5-tetracarbonitrile (BzCN) as the electron acceptor induced the formation of the CT complex.

Lone Pair Electrons with Weak Nuclear Binding Inducing Sensitive Nonlinear Optical Responses in Phosphorus Clusters.

Phosphorus clusters have broadband optical responses, adjustable geometries, and electronic structures, potentially balancing transparency and nonlinearity. In this study, the optical properties of phosphorus clusters are analyzed by using first-principles calculations. Phosphorus clusters exhibit strong light absorption in the ultraviolet region while remaining transparent in the visible to far-infrared bands. Importantly, the third-order nonlinear optical performance of phosphorus clusters surpasses that of p-nitroaniline with a D-π-A structure. The analysis reveals that lone pair electrons with weak nuclear binding induce sensitive nonlinear optical responses of phosphorus clusters. Furthermore, a practical approach for enhancing nonlinear optical effects in a medium via atom replacement and its application to hydride systems are discussed. Lone pair electron materials provide an alternative to conventional organic π-conjugated molecules for nonlinear optical devices, while potentially achieving a better trade-off of nonlinearity versus transparency. This study provides a novel concept for the development of high-performance nonlinear optical materials.

Ultrafast Electronic Coupling Estimators: Neural Networks versus Physics-Based Approaches.

Fast and accurate estimation of electronic coupling matrix elements between molecules is essential for the simulation of charge transfer phenomena in chemistry, materials science, and biology. Here we investigate neural-network-based coupling estimators combined with different protocols for sampling reference data (random, farthest point, and query by committee) and compare their performance to the physics-based analytic overlap method (AOM), introduced previously. We find that neural network approaches can give smaller errors than AOM, in particular smaller maximum errors, while they require an order of magnitude more reference data than AOM, typically one hundred to several hundred training points, down from several thousand required in previous ML works. A Δ-ML approach taking AOM as a baseline is found to give the best overall performance at a relatively small computational overhead of about a factor of 2. Highly flexible π-conjugated organic molecules like non-fullerene acceptors are found to be a particularly challenging case for ML because of the varying (de)localization of the frontier orbitals for different intramolecular geometries sampled along molecular dynamics trajectories. Here the local symmetry functions used in ML are insufficient, and long-range descriptors are expected to give improved performance.

Self-Assembled π-Conjugated Organic/Polymeric Microresonators and Microlasers

Optical microresonators are minute dielectric objects that are utilized as essential components in micrometer-scale light and laser sources, optical integrated circuits, micro-displays, chemo- and biosensors, and so forth. Particularly, microresonators made from organic and polymeric materials find unique applications owing to its structural flexibility, color tunability, and functionality with simple fabrication process, low cost and low energy consumption. In this Account, we highlight our recent progress on the organic/polymeric microresonators made through precisely controlled self-assembly process. The microstructures display novel optical functions such as circularly polarized luminescence emission, lasers, light energy harvesters, optical gate operations, optical memories and authentications, and optical sensing for environmental changes and mechanical forces. Our methodology for the precise design and control of organic and polymeric microstructures, will bridge between nanometer-scale supramolecular chemistry and bulk materials and will pave the way toward flexible optical and laser applications. Precise control of microstructures by self-assembly of π-conjugated organic molecules and polymers offers materials with sophisticated optical functions such as optical resonators and lasers, circularly polarized luminescence emitters, optical logic gate operations, optical memories, and light energy harvesting, which are utilized as optical sensors for environmental changes and mechanical forces.

Molecular and Supramolecular Designs of Organic/Polymeric Micro-photoemitters for Advanced Optical and Laser Applications.

ConspectusFor optical and electronic applications of supramolecular assemblies, control of the hierarchical structure from nano- to micro- and millimeter scale is crucial. Supramolecular chemistry controls intermolecular interactions to build up molecular components with sizes ranging from several to several hundreds of nanometers using bottom-up self-assembly process. However, extending the supramolecular approach up to a scale of several tens of micrometers to construct objects with precisely controlled size, morphology, and orientation is challenging. Especially for microphotonics applications such as optical resonators and lasers, integrated optical devices, and sensors, a precise design of a micrometer-scale object is required. In this Account, we review the recent progress on precise control of microstructures from π-conjugated organic molecules and polymers, which work as micro-photoemitters and are suitable for optical applications.After the introduction on the importance of the control of the hierarchical structures from molecular assembly, we review supramolecular methodology for assembling molecules and supramolecules to form microstructures such as spheres and polygons with precisely controlled morphology and molecular orientations. The resultant microstructures act as anisotropic emitters of circularly polarized luminescence. We report that synchronous crystallization of π-conjugated chiral cyclophanes forms concave hexagonal pyramidal microcrystals with homogeneous size, morphology, and orientation, which clearly paves the way for the precise control of skeletal crystallization under kinetic control. Furthermore, we show microcavity functions of the self-assembled micro-objects. The self-assembled π-conjugated polymer microspheres work as whispering gallery mode (WGM) optical resonators, where the photoluminescence exhibits sharp and periodic emission lines. The spherical resonators with molecular functions act as long-distance photon energy transporters, convertors, and full-color microlasers. Fabrication of microarrays with photoswitchable WGM microresonators by the surface self-assembly technique realizes optical memory with physically unclonable functions of WGM fingerprints. All-optical logic operations are demonstrated by arranging the WGM microresonators on synthetic and natural optical fibers, where the photoswitchable WGM microresonators act as a gate for light propagation via a cavity-mediated energy transfer cascade. Meanwhile, the sharp WGM emission line is appropriate for utilization as optical sensors for monitoring the mode shift and mode splitting. The resonant peaks sensitively respond to humidity change, absorption of volatile organic compounds, microairflow, and polymer decomposition by utilizing structurally flexible polymers, microporous polymers, nonvolatile liquid droplets, and natural biopolymers as media of the resonators. We further construct microcrystals from π-conjugated molecules with rods and rhombic plates, which act as WGM laser resonators with light-harvesting function. Our developments, precise design and control of organic/polymeric microstructures, form a bridge between nanometer-scale supramolecular chemistry and bulk materials and pave the way toward flexible micro-optics applications.