Azulene is a nonbenzenoid aromatic hydrocarbon with unique physicochemical properties. Herein, we report a brand new class of poly(vinyl arene)s constructed by azulene units, poly(vinyl azulene)s (PVAzs). The azulene units endow the PVAz polymers with diverse chemical structures and new properties. Due to the inherent dipole moment of the azulene unit, poly(2-vinyl azulene) exhibits a higher glass transition temperature (141 degrees C) and a smaller water contact angle (81.7 degrees) relative to atactic polystyrene (similar to 100 degrees C, 91.1 degrees). The dipole orientation of the azulene unit generates a great effect on the thermal and electrochemical properties, hydrophilicity, and proton-responsive ability of the PVAz polymers. Based on the feature of gaining and losing protons reversibly, the PVAz polymers have been used as additives to enhance the proton conductivity of Nafion and successfully used in hydrogen fuel cells with much-improved performance. This work opens up a way for developing new poly(vinyl arene)s by using vinyl azulenes and exploring their potential functions and applications.

Molecule-electrode interactions are critical for determining transport mechanisms and device functionalities in both single-molecule electrochemistry and electronics. Crucial factors such as anchoring groups and local fields have been studied, but the role of electrolytes and interfacial charge distribution remains largely underexplored. The present research focuses on how the interfacial charge distribution in the electric double layer (EDL) controls single-molecule junctions anchored by azulene. This probe molecule is chosen for its distinct charge properties in its 5- and 7-membered condensed ring structures that impose unique sensitivity to the surrounding electric field. Using scanning tunneling microscopy break junction (STM-BJ) techniques, we systematically investigate the conductance, anchoring sites, and coupling strength of these junctions in organic liquid but non-electrolytic environments, in aqueous solution under varying ionic strengths, and across different electrode systems and potential profiles. Our results demonstrate that the conductance and molecule-electrode coupling modes can be effectively tuned through control of interfacial charge distribution, particularly by altering the ion distribution around the electrodes. Mechanical modulation experiments substantiate these trends, and theoretical calculations pinpoint ion distribution as a key driver of molecule-electrode interaction. This research introduces a novel approach to dynamic control of the azulene-electrode coupling through electrolyte manipulation, offering entirely new insight for the design of electrolyte-responsive, switchable single-molecule devices.

Azulene, a nonalternant and nonbenzenoid hydrocarbon, has drawn increasing attention for constructing optoelectronic materials owing to its unique electronic structure and physicochemical properties. It is still a challenge to control the dipole orientation of azulene units in the backbone of 2,6-azulene-based conjugated polymers. Herein, three 2,6-azulene and bi-thieno[3,4-c]pyrrole-4,6-dione (BTPD) based conjugated copolymers P(AzBTPD-1), P(AzBTPD-2), and P(AzBTPD-3) with different dipole arrangements of azulene moieties were synthesized by direct arylation polymerization, where the rational design of the monomers allows for the achievement of the precisely controlled orientation of azulene units in the polymer main chain. The dipole arrangements of 2,6-azulene units were random for P(AzBTPD-1), head-to-head and tail-to-tail-arranged for P(AzBTPD-2) and head-to-tail-arranged for P(AzBTPD-3). High-temperature gel permeation chromatography of P(AzBTPD-1), P(AzBTPD-2), and P(AzBTPD-3) at 150 degrees C with 1,2,4-trichlorobenzene as the eluent gave average molecular weight values of 20.8, 20.7, and 24.1 kDa, respectively, with the corresponding polydispersity index values of 2.22, 2.48, and 2.17, respectively. All three polymers have similar molecular weights, thereby the influence of molecular weight can be ignored. UV-vis absorption spectra and cyclic voltammetry were performed to evaluate the optoelectronic properties of these three polymers. The maximum absorption wavelength of P(AzBTPD-1), P(AzBTPD-2), and P(AzBTPD-3) in thin film showed red shifts (8, 11 and 17 nm) relative to those in chloroform solution. The largest red shift of 17 nm of P(AzBTPD-3) indicated its strong intermolecular interactions in solid state. The energy levels of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of P(AzBTPD-1), P(AzBTPD-2), and P(AzBTPD-3) were -5.27/-3.56 eV, -5.27/-3.58 eV and -5.27/-3.59 eV, respectively, which were acquired by cyclic voltammetry measurements. Due to the electron-withdrawing property of BTPD, these three polymers did not show obvious proton responsiveness, and their UV-vis absorption spectra show no obvious change upon protonation. To investigate the effect of azulene dipole arrangements in the polymeric backbone on the charge transport properties of these polymers, bottom-gate and top-contact organic field-effect transistor (OFET) devices based on these three polymers were fabricated. Under nitrogen atmosphere, all three polymers showed unique n-channel charge transport behaviors. The thermal annealed OFETs based on P(AzBTPD-1), P(AzBTPD-2), and P(AzBTPD-3) showed electron mobilities of 0.011, 0.019 and 0.027 cm(2) V-1 s(-1), respectively. The higher electron-transport ability of P(AzBTPD-3) is consistent with the better degree of polymer order and the lower LUMO energy level obtained from cyclic voltammetry measurement. Examination of thin films via atomic force microscopy (AFM) provides the evidence of the best morphology of P(AzBTPD-3) among three polymers, which is in accordance with its best device performance. The root mean square roughness (RMS) values of thin films of these three polymers decreased after thermal annealing treatment, indicating the improved thin film morphology of these three polymers, which is consistent with the gradually enhanced performance of these polymers' OFET devices. Therefore, regulation the dipole arrangements of 2,6-azulene units in the polymeric backbone is an effective strategy for obtaining high-performance organic optoelectronic materials. Our work not only presented an efficient strategy to achieve the precisely controlled structural regularity of 2,6-azulene-based conjugated polymers, but also gave new insights for the synthetic chemistry of polymers with low-symmetrical conjugated monomers and the study of their structure-property relationships.

Azulene has aroused widespread interest for constructing optoelectronic materials. However, controlling the dipole orientation of 2,6-azulene units in the conjugated polymer backbone is a significant challenge so far. Herein, by C-H activation strategy, three 2,6-azulene-TPD-based conjugated copolymers with different dipole arrangements were synthesized, where TPD = thieno[3,4-c]pyrrole-4,6-dione. The dipole arrangements of 2,6-azulene units were random for P(AzTPD-1), head-tohead/tail-to-tail for P(AzTPD-2), and head-to-tail for P(AzTPD3). These polymers exhibited unipolar n-type semiconductor characteristics in organic field effect transistors. Moreover, regioregular polymer P(AzTPD-3) displayed the best device performance with an electron mobility of up to 0.33 cm2 V-1 s-1, which makes P(AzTPD-3) a high-performance n-type polymeric semiconductor. These results demonstrate that incorporation of 2,6-azulene units into the polymeric backbone together with the regulation of the dipole orientation of 2,6-azulene units is an effective strategy for obtaining high-performance organic optoelectronic materials.

Azulene has attracted significant attention for constructing novel optoelectronic materials. Tuning the dipole orientation of azulene unit in azulene-based conjugated polymers has recently aroused widespread concern and remains a great challenge due to the lack of synthetic method. Herein, we report three 2,6-azulene and 3,4-propylenedioxythiophene (ProDOT) based conjugated copolymers P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) with different dipole arrangements of azulene moieties. The regioregularity of these 2,6-azulene-ProDOT-based conjugated polymers was tuned by monomer design and direct arylation polymerization strategy, which enables a thorough study of the impact of the regioregularity on the properties of these polymers and their charge transport performance. The dipole orientation of 2,6-azulene units were regiorandom for P(AzProDOT-1), regularity with medium regioregularity for P(AzProDOT-2) and regularity with high regioregularity for P(AzProDOT-3), respectively. The number-average molecular weight values of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) estimated by gel permeation chromatography (GPC) were 11.1, 11.4 and 9.3 kDa, respectively, and the chemical structures of these three polymers were also characterized by high-temperature 1H NMR spectra. Ultraviolet-visible (UV-vis) absorption spectra and cyclic voltammetry were conducted to evaluate the optoelectronic properties of these polymers. The blue-shift of the maximum absorption peak for P(AzProDOT-2) indicates its twisted polymer backbone and short effective p-conjugation length, while the red-shift of the maximum absorption peak for P(AzProDOT-3) demonstrates the more planar conjugated skeleton and the longer effective p-conjugation length, although its molecular weight was a little lower. Besides, there was a prominent shoulder peak in the thin film of P(AzProDOT-3) in UV-vis absorption spectrum, indicating the stronger interchain interactions in solid state. All these observations were in agreement with the density functional theory (DFT) calculation results. Due to the electron-donating property of ProDOT, these three polymers displayed strong and sensitive proton responsiveness. The ultraviolet-visible-near infrared (UV-vis-NIR) spectra of these three polymers showed obvious red-shifts (>150 nm) upon protonation, and the films of these polymers also possess strong proton responsiveness properties. Charge-carrier mobilities of these three polymers were measured by the space-charge-limited current (SCLC). The hole mobilities of thin films of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) were 1.32x10(-5), 9.14x10(-5) and 1.41x10(-4) cm(2).V-1.s(-1), respectively, and their electron mobilities were 1.62x10(-6), 7.91x10(-6) and 1.66x10-5 cm(2).V-1.s(-1), respectively. The atomic force microscopy (AFM) study demonstrated that the thin film of P(AzProDOT-3) possessed the smoothest surface and the smallest root mean square (RMS) roughness,

A class of nonbenzenoid analogues of poly-(p-phenylenevinylene)-s (PPVs), 2,6-azulene-vinyl-based conjugated polymers (CPs) r -PAzV, hhtt -PAzV, and ht -PAzV, have been reported with different dipole arrangements of azulene units, where the five-membered ring and seven-membered ring of azulene core are defined as "head (H)" and "tail (T)", respectively. The PAzV polymers exhibit diverse backbone structures, proton responsiveness, an unusual relationship between crystallinity and regioregularity relative to conventional CPs, and balanced ambipolar charge transport. In regiorandom r -PAzV, the proportions of the H-T, H-H, and T-T linkages are about 40, 20, and 40%, respectively. The studies on solubility, thermal/optical properties, and microstructures of these PAzV polymers reveal that the presence of H-H and T-T arranged moieties in r -PAzV and hhtt -PAzV strengthens interchain interactions. Grazing-incidence wide-angle X-ray scattering measurements demonstrate enhanced long-range order with up to four orders of side-chain stacking reflections in as-spun films of r -PAzV and hhtt -PAzV. Williamson-Hall and Scherrer's analyses indicate that the lamellar crystallites in films of ht -PAzV have a much smaller size and lower crystallite quality relative to r -PAzV and hhtt -PAzV. Therefore, organic thin-film transistors based on r -PAzV and hhtt -PAzV display 2-4 orders higher charge carrier mobilities than those of ht -PAzV-based devices. The poor device performance of ht -PAzV might be attributed to the gradient electrostatic potential distribution and localized distribution of the Frontier molecular orbitals of the main chain. Our work enriches the family of PPV-like polymers, achieves the regulation of dipole arrangements of 2,6-azulene units together with clear structural analysis, and discloses that the dipole arrangements of azulene units along the polymer backbone have a great influence on the assembly of polymer chains.

Linear polycyclic systems are promising candidates in the area of organic electronics. Herein, we present the syntheses of three azulene-indole (AzIn) fused polycyclic heteroaromatics (PHAs), AzIn-1, AzIn-2 and DGAzIn, which have nitrogens and nonhexagonal rings simultaneously. The chemical structures, optical and electrochemical properties of three AzIn-based PHAs have been investigated, as well as their protonation behaviors with trifluoroacetic acid (TFA). All three AzIn-based PHAs exhibit narrow optical band gaps with moderate to good air stability, anti-Kasha emission and reversible stimuli-responsiveness. Furthermore, these straightforward and simple synthetic routes would provide a new entry for constructing novel azulene-embedded pi-conjugates, especially for the seven-membered ring of azulene unit, wherein the regioselective transformation is not well developed.

Azulene is a nonalternant and nonbenzenoid hydrocarbon with bright blue color and a dipole moment of 1.08 D, and has received increasing attention due to its unique electronic structure and physicochemical properties. Herein, we report the design and synthesis of two types of azulene-based [4]helicene 1a/1b and 2 that contain isoelectronic B-N and C=C units at the electron-rich 1-position of azulene unit, respectively. Formation of the helical scaffolds is executed by the introduction of boron and alkyne to flexible biaryl precursors, where the Lewis acidic boron and alkyne were employed as "glue" to join two subunits into fully fused scaffolds via electrophilic boronation and platinum-catalyzed cycloisomerization of alkyne at the 1-position of azulene unit, respectively. All of azulene-based helicenes were investigated by ultraviolet visible (UV-vis) absorption spectra, cyclic voltammetry (CV) measurements and density functional theory (DFT) calculations. Additionally, 1a was further characterized by single crystal structure analysis. The results suggest that the introduction of B-N unit changed the electronic structure of the conjugated aromatic framework, leading to a narrow HOMO-LUMO gap. Moreover, the B-N unit also affects the aromaticity of the pi-system as revealed by nucleus-independent chemical shift (NICS) via time-dependent density functional theory (TD-DFT) calculation. The single crystal structure analysis demonstrates that 1a has a helically twisted framework and Plus (P)/Minus (M) enantiomers. However, the Gibbs activation energy (Delta G(not equal)(T)) of the enantiomerization at room temperature is too low to separate two enantiomers by chiral high performance liquid chromatography (HPLC). Furthermore, the B-N unit exhibits partial double bond character and the BN-containing six-membered ring shows weak aromaticity. 1a with a phenyl group exhibits the deboronization upon addition of trifluoroacetic acid (TFA) as well as a specific sensing behavior to fluoride ion. However, 1b shows no deboronization upon addition of TFA and no sensing behavior to fluoride ion due to its steric hindered mesityl (Mes) group, but has a reversible stimuli-responsiveness with acid and base, this proton-responsiveness is similar to all-carbon analogue 2.

Azulene is a non-benzenoid aromatic building block with unique chemical structure and physicochemical properties. By using the "bottom-up" synthetic strategy, we synthesized three azulene-embedded [n]helicenes ([n]AzHs, n=5, 6 and 7), in which one terminal azulene subunit was fused with n-2 benzene rings. P- and M-enantiomers were observed in the packing diagrams of [5]-, and [6]AzHs. However, P- and M-[7]AzHs could be isolated by recrystallization of the racemic mixture. These [n]AzHs were endowed with new properties through the azulene moiety such as low-lying first electric state (S-1), small optical energy gap and anti-Kasha emission. [6]-, and [7]AzHs exhibit strong chiroptical responses with high absorption dissymmetry factor (g(abs)) maxima of about 0.02, which is among the highest |g(abs)| values of helicenes in the visible range. These azulene-embedded [n]helicenes contribute to the non-benzenoid helicene library and allow the structure-property relationships to be better understood.

Two poly(2,6-azuleneethynylene)s (PAzE-1 and PAzE-2) were designed and synthesized. The 2,6-azulene units are head-to-tail-arranged in PAzE-1, while there are three types of orientations of 2,6-azulene units in PAzE-2: head-to-tail, head-to head, and tail-to-tail segments, of which the head-to-tail one accounts for about 27% (determined from 1H NMR spectra). Such a structural distinction endows the two polymers with different absorption spectra in solution and aggregation states as well as different thin-film morphologies, microstructures, and field-effect transistor (FET) performances, suggesting that the dipole orientation of azulene units in a polymer backbone may be a critical issue that deserves careful consideration during the molecular design and synthesis. PAzE-1 with an ordered dipole orientation has stronger aggregation even in a very dilute solution (10-6 M). PAzE-2 films have a higher in-plane microstructural order and lower surface roughness than PAzE-1 films; hence, the PAzE-2-based transistor devices exhibit 1-2 orders higher hole and electron mobilities. Unlike typical p-type alkyl-substituted poly(p-phenyleneethynylene)s (PPEs), PAzE-1 and PAzE-2 are ambipolar semiconductors.