Azulene in Polymers and Their Properties

Abstract

Azulene, a unique isomer of naphthalene, has received much interest from researchers in different fields due to its unusual chemical structure with a negatively charged 5‐membered ring fused with a positively charged 7‐membered ring. In particular, incorporation of azulene into polymers has led to many interesting properties. This minireview covers functionalization methods of azulene at its various positions of 5‐ and 7‐membered rings to form azulene derivatives including azulene monomers, and gives an overview of a wide range of azulene‐containing polymers including poly(1,3‐azulene), azulene‐based copolymers with connectivity at 1,3‐positions of the 5‐membered ring, or 4,7‐positions of the 7‐membered ring, as well as copolymers with azulene units as side chains. Their chemical and physical properties together with applications of azulene‐containing polymers have also been summarized.

Proton-responsive azulene-based conjugated polymer with nonvolatile memory effects

“…This is consistent with changes in the PAV after TFA treatment, in which PAV undergoes electrochemical oxidation in the presence of an applied electric field, losing an electron and thus producing azulene radical cations. 6,10,11,26 The existence of radical cations increased the conductivity of the film, allowing the Al/PAV/ITO device to switch from a low-conductivity state to a high-conductivity state. More importantly, when a reverse voltage of −2 V was applied, the oxidized film was restored to its initial state, and the device returned to a low-conductivity state.…”

“…It exhibits properties different from small unsaturated aromatic hydrocarbons, showing a dark blue color and a dipole moment of 1.08 D. This high dipole moment is due to electron transfer from the seven-membered ring to the five-membered ring. 4–6 In addition, since azulene molecules can form stable seven-membered ring cations and heteroaromatics with high hole motilities, 7 they can be used in electrochromic devices, infrared detectors, chemical sensors, solar cells, and semiconducting devices. 8–15 To apply azulene in electronic memory devices, we introduced azulene derivatives into polymeric materials with structures similar to traditional PPV and achieved excellent resistive memory performance through their special electrical properties and controllable electronic structure.…”

Synthesis and Halochromic Properties of 1,2,6‐Tri‐ and 1,2,3,6‐Tetra‐aryl Azulenes

“…[3][4][5] Upon exposure to acidic solutions, azulene takes up a proton at its 1-position to form the azulenium cation which is stabilized via a 6-π-electron aromatization of the seven-membered ring. [6] These properties have driven studies of the potential applications of azulene in advanced electronics, such as optoelectronic devices, [7][8][9][10][11][12] nonlinear optics, [13] charge transport, [14] and sensory applications, [15][16][17][18][19][20][21][22][23][24] which have been comprehensively reviewed elsewhere. [25][26][27] Azulene has also been incorporated into interesting molecules such as squaraine, [28] boron-dipyrromethene, [29] and porphyrin.…”

Chemical syntheses and salient features of azulene-containing homo- and copolymers

“…These intriguing features have encouraged researchers to use azulene derivatives as functional organic molecules in the field of optoelectronics [7][8][9][10][11][12][13][14]. Employing such stimuli-responsive, non-alternant hydrocarbon with oddmembered rings in the chemical synthesis of functional polymers is also an interesting proposition and such polymers can find promising applications in the organic electronics field such as organic field-effect transistors (OFET) and photovoltaic (PV) cells [15,16]. The synthesis of azulene-containing polymers can be envisaged through chemical and electrochemical means.…”