Electron Acceptor Moieties Research Articles

New donor-acceptor-donor type of organic semiconductors based on the regioisomers of diketopyrrolopyrroles: A DFT study

The present work describes computational studies on structural, electronic, charge transport and photovoltaic properties of donor-acceptor-donor (D-A-D) type of compounds based on two regioisomers of diketopyrrolopyrrole. Diketopyrrolo[3,4-c]pyrrole (DPP1), a well known electron acceptor moiety and its regioisomer diketopyrrolo[3,2-b]pyrrole (DPP2) are coupled with various electron donor groups containing fused ring system to obtain model compounds of D-A-D type of architecture. The donor groups include meta-benzodithiophene, ortho-benzodithiophene, carbazole, dithienopyrrole, dithienosilole and dithienothiophene. An analysis of their properties reveal that these compounds possess unique characteristics and advantages over each other. Density functional theory (DFT) calculations show that the DPP2-based compounds exhibit lower hole reorganization energy (λh) than the corresponding DPP1-based compounds, while the DPP1-based compounds have lower electron reorganization energy (λe) than the corresponding DPP2-based compounds, which is in line with the observed ionizational potential (IP) and electron affinity (EA) values. The calculated open circuit voltage (Voc) and the fill factor (FF) values of the DPP2-based compounds as donors with fullerene-like PC61BM as an acceptor are higher than the DPP1-based compounds as donors. Charge density difference (CDD) calculation shows DPP2 based compounds exhibit better intramolecular charge transfer (ICT) properties as compared to their DPP1 counterpart. The weaker electron-hole coherence may lead to easy exciton dissociation in case of DPP1-based compounds at donor/acceptor interface, which is also supported by their comparatively lower exciton binding energy as compared to DPP2 counterparts.

Highly Efficient Luminescent Solar Concentrators Based on Benzoheterodiazole Dyes with Large Stokes Shifts.

Five extended π-conjugated systems with electron donor (D) and acceptor (A) moieties have been synthesized. Their basic D-A-D structural motif is a benzothiadiazole unit symmetrically equipped with two thiophene rings (S2T). Its variants include 1) the same molecular framework in which sulfur is replaced by selenium (Se2T), also with four thiophene units (Se4T) and 2) a D'-D-A-D system having a N-carbazole donor moiety at one end (CS2T) and a D'-D-A-D-A' array with a further acceptor carbonyl unit at the other extremity (CS2TCHO). The goal is taking advantage of the intense luminescence and large Stokes shifts of the five molecules for use in luminescent solar concentrators (LSCs). All of them exhibit intense absorption spectra in the UV/Vis region down to 630 nm, which are fully rationalized by DFT. Emission properties have been studied in CH2 Cl2 (298 and 77 K) as well as in PMMA and PDMS matrices, measuring photoluminescence quantum yields (up to 98 %) and other key optical parameters. The dye-PMMA systems show performances comparable to the present state-of-the-art, in terms of optical and external quantum efficiencies (OQE=47.6 % and EQE=31.3 %, respectively) and flux gain (F=10.3), with geometric gain close to 90. LSC devices have been fabricated and tested in which the five emitters are embedded in PDMS and their wave-guided VIS luminescence feeds crystalline silicon solar cells.

Investigation into the influence of an acrylic acid acceptor in organic D-π-A sensitizers against phototoxicity

Photodynamic therapy (PDT) is a non-invasive, selective, and cost-effective cancer therapy. We previously reported that thiophene-based organic D-π-A sensitizers consist of an electron-donating (D) moiety, a π-conjugated bridge (π) moiety, and an electron-accepting (A) moiety, and are readily accessible and stable templates for photosensitizers that could be used in PDT. In addition, acrylic acid acceptor-containing photosensitizers exert a high level of phototoxicity. This study was an investigation into 1) the possibility of increasing phototoxicity by introducing another carboxyl group or by replacing a carboxyl group with a pyridinium group, and 2) the importance of an alkene in the acrylic acid acceptor for phototoxicity. A review of the design, synthesis, and evaluation of sensitizers revealed that neither dicarboxylic acid nor pyridinium photosensitizers enhance phototoxicity. An evaluation of a photosensitizer without an alkene in the acrylic acid moiety revealed that the alkene was not indispensable in the pursuit of phototoxicity. The obtained results provided new insight into the design of ideal D-π-A photosensitizers for PDT.

Theoretical modifications of the molecular structure of Aurantinidin and Betanidin dyes to improve their efficiency as dye-sensitized solar cells

Two modifications of the molecular structures of Aurantinidin and Betanidin dyes were modeled, and the optical and electrical properties were calculated by using density functional theory (DFT) and time-dependent DFT (TD–DFT). The modification of the structures was done by connecting the units through vinyl groups and using regular electron acceptor and electron donor moieties to the original structures. It has been demonstrated that the modifications improved the electron injection properties of the molecules with higher light-harvesting efficiencies, an increase in the driving force of electron injection ($$\Delta G_{\text{inject}}$$), better regeneration energies ($$\Delta G_{\text{reg}}$$) and open-circuit photovoltages ($$V_{\text{OC}}$$).

Elucidating the aryl hydrocarbon receptor antagonism from a chemical-structural perspective

ABSTRACTThe aryl hydrocarbon receptor (AhR) plays an important role in several biological processes such as reproduction, immunity and homoeostasis. However, little is known on the chemical-structural and physicochemical features that influence the activity of AhR antagonistic modulators. In the present report, in vitro AhR antagonistic activity evaluations, based on a chemical-activated luciferase gene expression (AhR-CALUX) bioassay, and an extensive literature review were performed with the aim of constructing a structurally diverse database of contaminants and potentially toxic chemicals. Subsequently, QSAR models based on Linear Discriminant Analysis and Logistic Regression, as well as two toxicophoric hypotheses were proposed to model the AhR antagonistic activity of the built dataset. The QSAR models were rigorously validated yielding satisfactory performance for all classification parameters. Likewise, the toxicophoric hypotheses were validated using a diverse set of 350 decoys, demonstrating adequate robustness and predictive power. Chemical interpretations of both the QSAR and toxicophoric models suggested that hydrophobic constraints, the presence of aromatic rings and electron-acceptor moieties are critical for the AhR antagonism. Therefore, it is hoped that the deductions obtained in the present study will contribute to elucidate further on the structural and physicochemical factors influencing the AhR antagonistic activity of chemical compounds.

Boron(iii) β-diketonate-based small molecules for functional non-fullerene polymer solar cells and organic resistive memory devices.

A class of acceptor–donor–acceptor chromophoric small-molecule non-fullerene acceptors, 1–4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from −3.65 to −3.72 eV) and relatively high electron mobility (7.49 × 10−4 cm2 V−1 s−1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.

Biowaste-source-dependent synthetic pathways of redox functional groups within humic acids favoring pentachlorophenol dechlorination in composting process

Humic acids (HAs) can function as electron mediators for contaminants transformation in different environments. The humus respiration can facilitate pentachlorophenol (PCP) dechlorination during different biowastes composting. However, different characteristics of synthetic pathways of redox functional groups within HAs during different biowastes composting have never been characterized. Herein, we assessed the synthetic pathways of redox functional groups within HAs from protein-, lignocellulose-, and lignin-rich composts that facilitated the microbially reductive dechlorination of PCP, respectively. The results show that the aromatic systems are the major electron-accepting moieties of HAs and function as electron shuttles to facilitate the PCP dechlorination. Amino acid and reducing sugar are the major precursors for the synthesis of redox functional groups within HAs in protein-rich composts, and polyphenols and amino acids are discerned as the significant components to synthesize redox functional groups of HAs in lignocellulose- and lignin-rich composts. Seven groups of bacterial communities based on relationships among remarkable precursors, key bacterial communities, and redox functional groups within HAs are classified as participants in the precursors’ catabolism and aromatic system’ anabolism. Furthermore, the significant environmental factors on the synthetic pathways of redox functional groups within HAs in composting are confirmed by structural equation models. Conclusively, the regulating methods for promoting PCP dechlorination by HAs during different biowastes composting are proposed. Our results can help in understanding the distinct formative mechanisms of redox functional groups within HAs during different biowastes composting, providing insights into a classification-oriented approach for recycling utilization of different biowastes.

Photoinduced Electron Transfer Involving a Naphthalimide Chromophore in Switchable and Flexible [2]Rotaxanes.

The interlocking of ring and axle molecular components in rotaxanes provides a way to combine chromophoric, electron-donor and electron-acceptor moieties in the same molecular entity, in order to reproduce the features of photosynthetic reaction centers. To this aim, the photoinduced electron transfer processes involving a 1,8-naphthalimide chromophore, embedded in several rotaxane-based dyads, were investigated by steady-state and time-resolved absorption and luminescence spectroscopic experiments in the 300 fs-10 ns time window. Different rotaxanes built around the dialkylammonium/ dibenzo[24]crown-8 ether supramolecular motif were designed and synthesized to decipher the relevance of key structural factors, such as the chemical deactivation of the ammonium-crown ether recognition, the presence of a secondary site for the ring along the axle, and the covalent functionalization of the macrocycle with a phenothiazine electron donor. Indeed, the conformational freedom of these compounds gives rise to a rich dynamic behavior induced by light and may provide opportunities for investigating and understanding phenomena that take place in complex (bio)molecular architectures.

Design and synthesis of benzimidazole phenol-porphyrin dyads for the study of bioinspired photoinduced proton-coupled electron transfer

Benzimidazole phenol-porphyrin dyads have been synthesized to study proton-coupled electron transfer (PCET) reactions induced by photoexcitation. High-potential porphyrins have been chosen to model P680, the photoactive chlorophyll cluster of photosynthetic photosystem II (PSII). They have either two or three pentafluorophenyl groups at the meso positions to impart the high redox potential. The benzimidazole phenol (BIP) moiety models the Tyr[Formula: see text]-His190 pair of PSII, which is a redox mediator that shuttles electrons from the water oxidation catalyst to P680[Formula: see text]. The dyads consisting of a porphyrin and an unsubstituted BIP are designed to study one-electron one-proton transfer (E1PT) processes upon excitation of the porphyrin. When the BIP moiety is substituted with proton-accepting groups such as imines, one-electron two-proton transfer (E2PT) processes are expected to take place upon oxidation of the phenol by the excited state of the porphyrin. The bis-pentafluorophenyl porphyrins linked to BIPs provide platforms for introducing a variety of electron-accepting moieties and/or anchoring groups to attach semiconductor nanoparticles to the macrocycle. The triads thus formed will serve to study the PCET process involving the BIPs when the oxidation of the phenol is achieved by the photochemically produced radical cation of the porphyrin.

Use of Pyrimidine and Pyrazine Bridges as a Design Strategy To Improve the Performance of Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes.

We present a study of two isomeric thermally activated delayed fluorescence (TADF) emitters 9,9'-(sulfonylbis(pyrimidine-5,2-diyl))bis(3,6-di-tert-butyl-9H-carbazole) (pDTCz-DPmS) and 9,9'-(sulfonylbis(pyrazine-5,2-diyl))bis(3,6-di-tert-butyl-9H-carbazole) (pDTCz-DPzS). The use of pyrimidine and pyrazine as bridging units between the electron donor and acceptor moieties is found to be advantageous compared to the phenyl- (pDTCz-DPS) and pyridine-based analogues (pDTCz-3DPyS and pDTCz-2DPyS). Conformational modulation of the donor groups as a function of the bridge results in high photoluminescence quantum yields (ΦPL > 68%) and small energy gaps between singlet and triplet excited states (ΔEST < 160 meV). OLEDs using pDTCz-DPmS and pDTCz-DPzS as emitters exhibit blue and green electroluminescence, respectively, with higher maximum external quantum efficiencies (EQEmax of 14% and 18%, respectively) and a reduced efficiency roll-off as compared to the reference devices using pDTCz-DPS, pDTCz-3DPyS, and pDTCz-2DPyS as the emitters. Our results provide a more complete understanding on the impact of the bridge structure in D-A-D TADF systems on the optoelectronic properties of the emitter and how the balance between color purity and EQE in the devices can be controlled, advancing the design strategies for TADF emitters.

Photostable Voltage-Sensitive Dyes Based on Simple, Solvatofluorochromic, Asymmetric Thiazolothiazoles.

A family of asymmetric thiazolo[5,4-d]thiazole (TTz) fluorescent dye sensors has been developed, and their photophysical sensing properties are reported. The π-conjugated, TTz-bridged compounds are synthesized via a single-step, double condensation/oxidation of dithiooxamide and two different aromatic aldehydes: one with strong electron-donating characteristics and one with strong electron-accepting characteristics. The four reported dyes include electron-donating moieties (N,N-dibutylaniline and N,N-diphenylaniline) matched with three different electron-accepting moieties (pyridine, benzoic acid, and carboxaldehyde). The asymmetric TTz derivatives exhibit strong solvatofluorochromism with Stokes shifts between 0.269 and 0.750 eV (2270 and 6050 cm-1) and transition dipole moments (Δμ = 13-18 D) that are among the highest reported for push-pull dyes. Fluorescence quantum yields are as high as 0.93 in nonpolar solvents, and the fluorescence lifetimes (τF) vary from 1.50 to 3.01 ns depending on the solvent polarity. In addition, thermofluorochromic studies and spectrophotometric acid titrations were performed and indicate the possibility of using these dyes as temperature and/or acid sensors. In vitro cell studies indicate good cell membrane localization, negligible cytotoxicity, promising voltage sensitivities, and photostabilities that are 4 times higher than comparable dyes. Their ease of synthesis and purification, remarkable photophysical properties, and chemically sensitive TTz π-bridge make these asymmetric dye derivatives attractive for environmental and biological sensing or similar molecular optoelectronic applications.

Blue thermally activated delayed fluorescence emitter using modulated triazines as electron acceptors

Three types of thermally activated delayed fluorescence (TADF) emitters, namely, moTrSAc, tmTrSAc, and motmTrSAc, are reported that emit blue-shifted emission with high external quantum efficiencies (EQEs). These emitters have electron donating spiroacridine in common and various triazine-based electron acceptors. The electronic and structural control on the electron acceptor moiety adjusts the reduction potential of the molecule to shift the emission wavelength to the blue region. Moreover, as these emitters become widened, the light out-coupling efficiency increases due to the enhanced horizontal emitting dipole orientation. As a result, OLEDs based on moTrSAc, tmTrSAc, and motmTrSAc emit blue light in a range of 460–480 nm with high EQEs of 21.3, 15.5, and 19.5%, respectively.

Theoretical Study of Ground- and Excited-State Charge Transfer in Fulvene-Based Donor-Acceptor Systems.

Donor-acceptor systems based on fulvene as the electron-accepting moiety are typified by exotic, strongly polar electronic structures. In this contribution, ab initio calculations have been performed to explore the ground- and excited-state properties of an archetypal compound of this class, which incorporates the exocyclic carbon atom of fulvene into a tetramethylimidazoline-like five-membered ring. In the electronic ground state, the compound under study has a pronounced zwitterionic character and is best described as consisting of a negatively charged cyclopentadienyl ring linked covalently to a positively charged tetramethylimidazolium ring. Both of these rings can be considered as aromatic. The excess negative charge localized on the cyclopentadienyl ring is highly labile in the photochemical sense: the low-lying valence excited states exhibit varying degrees of reverse charge transfer, whereby electron density is transferred from the cyclopentadienyl ring back onto the tetramethylimidazolium ring. The topographies of the excited-state potential energy surfaces favor rapid and efficient internal conversion at an extended, fulvene-like S1/S0 conical intersection seam. As a consequence, the excited-state lifetime of this compound is predicted to be on the order of 100 fs.

Effects of electron donating and accepting moieties on electrical memory behaviors of polymers

In this study, three different series of vinyl copolymers bearing electron donating and accepting moieties in various compositions and their homopolymers were synthesized by reversible addition-fragmentation chain transfer polymerizations. They all were soluble in conventional organic solvents and gave good quality nanoscale films via conventional coating and drying processes. They were thermally stable up to 242 °C or higher temperatures. Their optical and electrochemical properties as well as electron densities and mass densities were measured. The nanoscale film morphologies were further examined by synchrotron grazing incidence X-ray scattering analysis; they were confirmed as amorphous or structurally-featureless films. All polymers exhibited various electrical properties depending on the polymers and film thicknesses. In particular, only p-type digital memory characteristics were observed within certain film thickness windows, regardless of electron-donating polymers, electron-accepting polymers, and their copolymers. Moreover, all polymers revealed high memory performances with low switching-ON voltages, high ON/OFF current ratios and high reliabilities even in air ambient conditions. The memory behaviors followed a combination of hopping conduction and trap-limited space charge limited conduction in the OFF-state and hopping conduction in the ON-state. However, the film thickness window showing digital memory characteristics was significantly dependent upon the compositions of electron donating and accepting moieties. Higher fraction of electron-donating moieties provided wider film thickness window for digital memory. For this aspect, the electron-accepting polymers could gain great benefits by incorporating electron-donating moieties, whereas the electron-donating polymers could attain only negative impacts via the addition of electron-accepting moieties. Overall, all polymers of this study are suitable for the low-cost mass production of high-performance programmable memory devices.

Tuning electronic properties of molecular acceptor-π-porphyrin-π-acceptor donors via π-linkage structural engineering

Abstract Three new molecular A-π-D-π-A type donors, P1, P2 and P3, comprising an alkylthiothienyl substituted porphyrin electron donor core (D) and two 3-ethylrhodanine electron acceptor moieties (A) connected peripherally to the porphyrin core via respectively a monomeric, dimeric or trimeric phenylethynyl π-linkage, are synthesized and studied for their optoelectronic, charge transport, and photovoltaic properties. The hole mobilities of their blend films with PC71BM follow the order of P3> P2 > P1 in hole-only device. When used as electron donors with fullerene acceptor, PC71BM, in conventional bulk heterojunction organic solar cells, the optimal device with P1 donors shows a lower FF, but an intensity stronger and broader EQE, the highest JSC and VOC. As a whole, the PCEs of their optimal devices follow the order of P1> P2 > P3, corresponding to 8.61%, 8.20% and 7.82%, respectively. These results clearly demonstrate the decisive influence of π–linkage length over photovoltaic performance, and that the shorter the π–linkage length the better the photovoltaic performance.

One-Step Construction of Fluorenone-Based Donor-Acceptor-Type Conjugated Polymers via Direct Arylation Polymerization for Cell-Imaging Applications.

Direct arylation polymerization (DARP) is a novel approach to obtain conjugated polymers (CPs) through the straightforward C-H activation of monomer building blocks. In this work, a convenient DARP method with high efficiency and excellent regioselectivity is developed to synthesize a series of donor-acceptor (D-A)-type CPs composed of electron-acceptor moiety fluorenones (FOs) and various electron-donor moieties. CPs with different band gaps are obtained in good yields and display large Stokes shifts up to 295 nm. Two ionic CPs, PFOP-NEt3(+) and PFOP-COO(-), were prepared in a polar solvent system to improve the water solubility and biocompatibility using the proposed DARP method. Detailed photophysical studies of these two CPs suggest that both solvation and hydrogen bonds play important roles in determining the polymers' spectroscopic properties. Further studies of the cationic polymer PFOP-NEt3(+) in cell imaging demonstrate its potential application in labeling cell membranes and lysosomes given its low cytotoxicity, excellent photostability, and specific subcellular localization.

Linked Donor-Acceptor Systems for Symmetric Nonaqueous Redox Flow Batteries

A series of molecules containing electron donor and acceptor moieties were synthesized and analyzed for potential future use in redox flow batteries (RFBs). These compounds, including D-A, D-A-D, and A-D-A alkyl-linked systems, can exist in at least three stable oxidation states: an oxidized (catholyte) form, a reduced (anolyte) form, and the neutral species. For this study, donors included various organic heterocycles, while acceptors included several imides and diimides. In all cases, cyclic voltammetry revealed highly reversible electrochemical behavior for both the individual redox active moieties as well as for the fully linked system. This approach provides for the independent optimization of anolyte and catholyte properties, while the covalent linkage results in a symmetric system whereby both RFB half-reactions generate an identical product (the neutral species). In principle, this may allow for elimination of the ubiquitous and expensive ion exchange membrane used in typical RFBs. Because the membrane can account for up to 40% of cell costs, this could represent an important opportunity to improve the economics of employing flow batteries for grid-level energy storage applications. The synthesis, characterization and preliminary electrochemical investigation of these molecules will be described. Figure 1

(Invited) Photoinduced Charge Separation in Several Dyads Involving Fullerenes

Conversion of the sunlight into chemical energy is considered to be one of the most important and fundamental chemical reactions in nature. A broad variety of artificial photosynthetic systems based on dyads, triads and up to pentads involving electron donor and acceptor moieties have been designed and synthesized in order to investigate artificial photoinduced energy and electron transfer processes. In this work, we discuss a series of computational studies that involves the photoinduced charge separation in metal-cluster encapsulated triphenylamine-[80]fullerenes,[1] in a transition-metal complex linked to a fullerene moiety,[2] in an all-fullerene hetero-dumbbell formed by two fullerene units, namely C60 as the electron acceptor component and endohedral Lu3N@C80 as the donor unit,[3] and in four akamptisomers of quinoxalinoporphyrin–[60]fullerene complex.[4] References [1] J. P. Martínez, M. Solà and A. A. Voityuk. Chem. Eur. J. 22 (2016) 17305. [2] A. J. Stasyuk, O. A. Stasyuk, S. Filippone, N. Martín, M. Solà and A. A. Voityuk. Chem. Eur. J., 24 (2018) 13020. [3] Manuscript in preparation [4] A. J. Stasyuk, O. A. Stasyuk, M. Solà and A. A. Voityuk. Chem. Eur. J., 2019, ASAP, DOI: 10.1002/chem.201804999 Figure 1

Synthesis of Cyano-Substituted Conjugated Polymers for Photovoltaic Applications.

Three conjugated polymers, in which the electron-donating (D) 5-alkylthiophene-2-yl-substitued benzodithiophene was linked to three different electron-accepting (A) moieties, i.e., benzothiadiazole (BT), diphenylquinoxaline (DPQ), and dibenzophenazine (DBP) derivative via thiophene bridge, were synthesized using the Stille coupling reaction. In particular, the strong electron-withdrawing cyano (CN) group was incorporated into the A units BT, DPQ, and DBP to afford three D–A type target polymers PB–BTCN, PB–DPQCN, and PB–DBPCN, respectively. Owing to the significant contribution of the CN-substituent, these polymers exhibit not only low-lying energy levels of both the highest occupied molecular orbital and the lowest unoccupied molecular orbital, but also reduced bandgaps. Furthermore, to investigate the photovoltaic properties of polymers, inverted-type devices with the structure of ITO/ZnO/Polymer:PC71BM/MoO3/Ag were fabricated and analyzed. All the polymer solar cells based on the three cyano-substituted conjugated polymers showed high open-circuit voltages (Voc) greater than 0.89 V, and the highest power conversion efficiency of 4.59% was obtained from the device based on PB-BtCN with a Voc of 0.93 V, short-circuit current of 7.36 mA cm−2, and fill factor of 67.1%.

How to Design Donor-Acceptor Based Heterocyclic Conjugated Polymers for Applications from Organic Electronics to Sensors.

Over the past few years, significant progress has been made in the design of organic semi-conducting conjugated polymers that readily transport holes or electrons and can result in light emission. The conjugated backbone consist mainly of electron-donating (donor) and electron-withdrawing (acceptor) units as alternating groups in a conjugated oligomer or polymer that can be regulated by physical properties such as π conjugation length, monomer alteration, inter/intramolecular interactions and energy levels. Certainly, it is notable today that the highest occupied molecular orbital level of the producing material is localized predominantly on the electron-donating moiety and lowest unoccupied molecular orbital level on the electron-accepting moiety. Conjugated oligomers or polymers are used in many detecting fields due to their exceptional ability to sense toxic chemicals, metal ions and biomolecules. The conjugated polymers have unique delocalized π-electronic "molecular wires" that can expand the fluorescence intensity considerably. The fluorescence intensity of polymers can be quenched by particular quenching molecules. In this review, the fluorescence intensity, detecting of multiple metal ions, solubility, photochemical stability and optoelectronic properties of these conjugated polymers, and how they can be regulated by different functional groups, are discussed in detail.