Linear Nonalternant Isomers of Acenes Fusing Multiple Azulene Units

Abstract

A modular approach to azulene building blocks was developed starting from readily available aryl-substituted cyclopentadiene and ortho-haloaryl aldehyde by dehydration condensation followed by palladium-catalyzed CÀ H coupling. It facilitates the synthesis of four nonalternant isomers of pentacene and hexacene, namely, dibenzo[e,g]azulene, benzo[1,2-f : 5,4f']diazulene, benzo[1,2-f : 4,5-f']diazulene, and naphtho[2,3-f : 6,7-f']diazulene, which exhibit narrow band gaps with high stability in addition to protonationcaused enhanced near-infrared fluorescence. We discovered that in these isomers, i) constitutional isomerism influences significantly their photoelectric properties and ii) the elongation of the conjugation system does not necessarily lead to a narrowing in the band gap. Due to the easy modifiability of the nonazulene building blocks, this strategy can be extended to modularly prepare numerous multiazulene-fused aromatics.

Angularly fused diaza-dinaphthopyrenes: regio-selective synthesis, crystal structures and isomer-dependent mechanochromic fluorescent properties

“…The magnitudes of NICS(1) zz values are more negative in 1,6-DNPy than in 1,8-DNPy , suggesting stronger diatropicity of 1,6-DNPy . 1 This observation corroborated the experimental finding that 1,6-DNPys possessed a higher conjugation degree. Both 1,8-DNPy and 1,6-DNPy exhibit interesting global aromaticity with clockwise ring current along the periphery of the whole backbone according to their ACID plots.…”

“…Acenes represent a family of polycyclic aromatic hydrocarbons (PAHs) with laterally fused benzene rings. 1 They have become the functional material of choice for various applications such as organic electronics, biomedical imaging, sensors etc. 2 In these scenarios, controlling the diverse field of acenes is of fundamental importance, whose key features lie in size, dimensionality and heteroaromatic doping.…”

“…3 These factors have significant impacts on their electronic band structure, and optical and mechanical properties, and also influence their packing in the solid state. 3 f In contrast to the development of long linear acenes, 1 the strategy of precisely doping N atoms into large angular acenes could increase the electron affinity, dipole moment and intermolecular interactions, and more importantly, stabilize the frontier molecular orbitals of the resultant π-extended 2D-azaacenes. 4 However, N-doping and π-extension both raise a considerable issue regarding regio-selective synthesis.…”

The road to bis‐periazulene (cyclohepta[def]fluorene): Realizing one of the long‐standing dreams in nonalternant hydrocarbons

“…[ 52 ] Liu's group reported the nonalternant isomers 26 – 29 of oligoacenes fusing multiple dibenzo[ e , g ]azulene units. [ 53 ] Azulene‐fused acenes 30 – 32 , which are isoelectronic to the pentacene, hexacene, and heptacene, respectively, were synthesized and characterized. [ 54 ] Experimental and theoretical investigations revealed that aromatic character is localized in the backbone comprising all of the six‐ and five‐membered rings whereas the seven‐membered ring remains non‐aromatic.…”

A nonalternant azulene-embedded carbon nanohoop featuring anti-Kasha emission and tunable properties upon pH stimuli-responsiveness

“…19 These unique properties endow azulene with great promise for developing advanced materials in organic semiconductors, 20 photoswitches, 21 nonlinear optical materials, 22 chemical sensing, bioimaging, 23 and nonplanar polycyclic aromatic hydrocarbons. 24 However, investigations associated with nonalternant aromatic all-carbon nanohoops with pH reversible stimuli-responsiveness remained largely unexplored to date because of the lack of suitable stimuli-responsive all-carbon building blocks. Most pH active materials normally require heteroatoms such as nitrogen, oxygen, and sulfur as proton acceptors.…”