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

Abstract

A series of novel 2,6‐functionalized azulene molecules Azu1‐3 with varied fluorene substituents at the 1‐ and 3‐positions of azulene as well as at the 5’‐position of 2‐thiophene group were synthesized. Their electronic absorption and emission spectra at neutral and protonated states were examined. It was found that after functionalization with fluorenyl groups, Azu1‐3 exhibited absorption maxima at 445, 451 to 468 nm, respectively. In contrast, their corresponding protonated species showed much redshifted absorption maxima at 560, 582 to 643 nm, respectively, mainly due to the extension of conjugation length and the large dipole moment along the C2v axis of 2,6‐substituted azulene molecules. Azu1‐3 are non‐fluorescent in their neutral forms, but became emissive in their protonated states. Analysis of absorption and emission spectra shows that substitution of the 1‐ or 3‐position of azulene led to decrease in response to trifluoroacetic acid.

Poly(2,6-azuleneethynylene)s: Design, Synthesis, and Property Studies

“…As shown in Figures a,b and S12, pronounced changes in absorption spectra and the color of the solutions are observed upon the addition of TFA. PAzE-1 and PAzE-2 show gradually red-shifted absorptions with the increase of TFA concentration, which can be attributed to the formation of azulenium cations in the backbones. , However, the proton-responsiveness of PAzE-1 and PAzE-2 is not sensitive because the 1- and 3-positions of the azulene units are occupied by two alkyl chains that increase the steric hindrance and the electron-deficient alkynyl may lower the electron density on the five-membered ring of the azulene unit. The spectral changes become less pronounced when TFA concentration is beyond 60 vol %, suggesting that the number of azulenium cations is close to saturation at this TFA concentration.…”

Effect of connectivity variation in azulene-BODIPY triads and their optoelectronic properties

“…Literature insights reveal that varying the connectivity of azulene leads to a significant change in properties of resulting systems. 6–8…”

“…Literature insights reveal that varying the connectivity of azulene leads to a significant change in properties of resulting systems. [6][7][8] Boron-dipyrromethene (4,4-difluoro-4-bora-3a,4a-diaza-sindacene, BODIPY) systems have garnered huge attention of researchers over the past two decades because of their interesting photophysical properties that include narrow absorption and emission bands, large molar absorption coefficients, and high fluorescence quantum yields. 9 They are finding applications in diverse fields, such as laser dyes, fluorescent probes, light-emitting diodes, OFETs, photosensitizers for solar cells, and several others.…”