Multicolour electrochromic materials have been considered as a promising alternative to achieve dynamic full-colour tuning towards next-generation electronic display technology. However, the development of electrochromics with wide colour gamut and subtle multicolour tunability still remains challenging due to inflexible energy level structures in intrinsic active materials. Herein, the electrochromic π-conjugated polymers with rich and subtle colour tunability were designed and developed based on a fine adjustment on the energy level structures. The chromatic transition covers almost full-colour gamut, and each colour scheme has a rich variety of categories stemming from versatile hues, chromas and lightnesses. Moreover, the multicolour π-conjugated polymers also demonstrate superior overall electrochromic performance, including fast switching (∼1.0 s), high colouration efficiency (160.4 cm2 C-1@550 nm) and good reversibility (over 90 % retention after 10,000 cycles). As a proof of concept, ultrathin and flexible prototype devices are developed by utilizing the multicolour π-conjugated polymers as electrochromic active layer, exhibiting a wide colour gamut and highly saturated multicolour tunability. The design principles proposed in this work may also be applicable to diverse optoelectronic applications.

Thiazole, as a family of five-membered heteroaromatic rings, is an interesting building unit that can play a role in coplanarizing the backbone as well as deepening the HOMO energy level, which is beneficial for the design of π-conjugated polymers for the photoactive materials in organic photovoltaics (OPVs). Here, we designed and synthesized π-conjugated polymers with simple chemical structures, which consist of 2,2\'-bithiazole or 5,5\'-bithiazole and alkylthiophenes as the polymer backbone. In fact, the polymers can be easily synthesized in much fewer steps compared to the typical high-performance polymers based on fused heteroaromatic rings. Interestingly, PTN5 exhibited a markedly higher ordered structure than PTN2. This was likely ascribed to the more coplanar and rigid backbone of PTN5 than that of PTN2 originating in the effectively arranged S···N interaction. As a result, the nonfullerene photovoltaic cell based on PTN5 showed a PCE of 12.2%, which was much higher than the cell based on PTN2 (4.3%) and was high for the polymers consisting of only nonfused rings. These results demonstrate that thiazole-based polymers are promising photoactive materials for OPVs and emphasize the importance of careful molecular design utilizing noncovalent interactions.

When irradiating a molecular material containing photo-isomerizable groups with pure circularly polarized light, a particular handedness may get imprinted into the material. To study the mechanism and kinetics of this process in situ and operando, we have developed a new chiroptical tool where the circular polarization of the incident circularly polarized light is monitored after transmission through the photoactive layer. Practical limits to the resolution and sensitivity of the measurements as well as its calibration are discussed. To aid interpretation of experimental results, we present kinetic Monte Carlo simulations on a model for the active material involving photo-induced reorientation of molecules in a cholesteric organization. The simulations support the interpretation of a transient minimum in the degree of circular polarization of the transmitted light in terms of a nematic transient state during photo-inversion of a cholesteric organization in the molecular material.

A new benzodithiophene and benzotriazole-based terpolymer bearing a fluorescein derivative as a side group was synthesized and studied for organic solar cell (OSC) applications. This side group was covalently bounded to the backbone through an n-hexyl chain to induce the intramolecular Förster Resonance Energy Transfer (FRET) process and thus improve the photovoltaic performance of the polymeric material. The polymer exhibited good solubility in common organic chlorinated solvents as well as thermal stability (TDT10% > 360 °C). Photophysical measurements demonstrated the occurrence of the FRET phenomenon between the lateral group and the terpolymer. The terpolymer exhibited an absorption band centered at 501 nm, an optical bandgap of 2.02 eV, and HOMO and LUMO energy levels of −5.30 eV and −3.28 eV, respectively. A preliminary study on terpolymer-based OSC devices showed a low power-conversion efficiency (PCE) but a higher performance than devices based on an analogous polymer without the fluorescein derivative. These results mean that the design presented here is a promising strategy to improve the performance of polymers used in OSCs.

The understanding and applications of electron-conducting π-conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n-doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n-doped backbone. Here, the n-type conducting NDI polymer with enhanced stability of its n-doped states for prospective \"in-water\" applications is developed. A combined experimental-theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10-2  S cm-1  under ambient conditions and 10-1  S cm-1  in vacuum. The modeling explains the stabilizing effects  for various dopants. The simulations show a significant doping-induced \"collapse\" of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n-doped states in water and the high electron conductivity of polymers.

Organic semiconductors inherently have a low dielectric constant and hence high exciton binding energy, which is largely responsible for the rather low power conversion efficiency of organic solar cells as well as the requirements to achieve delicate bulk-heterojunction nanophase separation in the active layer. In this study, methyl acrylate as a weakly electron-withdrawing side chain for the electron rich thiophene to prepare a new building block, methyl thiophene-3-acrylate (TA), with increased polarity is used. A wide bandgap polymer PBDT-TA synthesized using TA and a benzodithiophene (BDT) monomer shows increased dielectric constant and reduced exciton binding energy compared to the analogous polymer PBDT-TC, which is made of BDT and methyl thiophene-3-carboxylate (TC). An organic solar cell device based on PBDT-TA:ITIC also achieves a higher power conversion efficiency of 10.47% than that of the PBDT-TC:ITIC based solar cell (9.68%). This work demonstrates the effectiveness of using acrylate side chains to increase the dielectric constant, reduce the exciton binding energy, and enhance the solar cell efficiency of polymer semiconductors.

Owing to their extraordinary properties of π-conjugated polymers (π-CPs), such as light weight, structural versatility, ease of synthesis and environmentally friendly nature, they have attracted considerable attention as electrode material for metal-ion batteries (MIBs) and supercapacitors (SCPs). Recently, researchers have focused on developing nanostructured π-CPs and their composites with metal oxides and carbon-based materials to enhance the energy density and capacitive performance of MIBs and SCPs. Also, the researchers recently demonstrated various novel strategies to combine high electrical conductivity and high redox activity of different π-CPs. To reflect this fact, the present review investigates the current advancements in the synthesis of nanostructured π-CPs and their composites. Further, this review explores the recent development in different methods for the fabrication and design of π-CPs electrodes for MIBs and SCPs. In review, finally, the future prospects and challenges of π-CPs as an electrode materials for strategies for MIBs and SCPs are also presented.

Quantum phase transitions (QPTs) driven by quantum fluctuations are transitions between distinct quantum phases of matter. At present, they are poorly understood and not readily controlled. Here, scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) are used to explore atomic scale control over quantum phase transitions between two different topological quantum states of a well-defined π-conjugated polymer. The phase transition is driven by a pseudo Jahn-Teller effect that is activated above a certain polymer chain length. In addition, theoretical calculations indicate the presence of long-lasting coherent fluctuations between the polymer\'s two quantum phases near the phase transition, at finite temperature. This work thus presents a new way of exploring atomic-scale control over QPTs and indicates that emerging quantum criticality in the vicinity of a QPT can give rise to new states of organic matter.

π-Conjugated polymers have numerous applications due to their advantageous optoelectronic and mechanical properties. These properties depend intrinsically on polymer ordering, including crystallinity, orientation, morphology, domain size, and π-π interactions. Programming, or deliberately controlling the composition and ordering of π-conjugated polymers by well-defined inputs, is a key facet in the development of organic electronics. Here, π-conjugated programming is described at each stage of material development, stressing the links between each programming mode. Covalent programming is performed during polymer synthesis such that complex architectures can be constructed, which direct polymer assembly by governing polymer orientation, π-π interactions, and morphological length-scales. Solution programming is performed in a solvated state as polymers dissolve, aggregate, crystallize, or react in solution. Solid-state programming occurs in the solid state and is governed by polymer crystallization, domain segregation, or gelation. Recent progress in programming across these stages is examined, highlighting order-dependent features and assembly techniques that are unique to π-conjugated polymers. This should serve as a guide for delineating the many ways of directing π-conjugated polymer assembly to control ordering, structure, and function, enabling the further development of organic electronics.

Recent studies indicated that the toxicity of heavy metal ions caused a series of environmental, food, and human health problems. Chemical ionochromic sensors are crucial for detecting these toxicity ions. Incorporating organic ligands into π-conjugated polymers made them receptors for metal ions, resulting in an ionochromism phenomenon, which is promising to develop chemosensors for metal ions. This review highlights the recent advances in π-conjugated polymers with ionochromism to metal ions, which may guide rational structural design and evaluation of chemosensors.