Azulene-Fused Linear Polycyclic Aromatic Hydrocarbons with Small Bandgap, High Stability, and Reversible Stimuli Responsiveness

Abstract

Azulene-fused polycyclic aromatic hydrocarbons (PAHs) were synthesized from commercially available azulene in four steps. The resulting azulene conjugates exhibited significantly narrow HOMO-LUMO bandgaps with high air stability, confirmed by photophysical study. Introduction of azulene also enabled the unique reversible stimuli-responsiveness even with the weak acid and base, which can potentially control the degree of conjugation and optoelectronic properties by simple acid-base and redox processes.

In the quest for a stable triplet state in small polyaromatic hydrocarbons: an in silico tool for rational design and prediction

“…The ST gaps with various levels of multireference theory (CASSCF and CASPT2) show the same qualitative trend (given in the ESI †). It is important to note that when the acenes and azulenes are fused in different orders, 51 i.e., structures with fused 7-5-6 or 7-5-6-6 rings, they show much higher (1.58 and 1.40 eV respectively) adiabatic ST gaps than 7-6-5 or 7-6-6-5 motifs (0.97 and 0.46 eV respectively) calculated at the DMRG/cc-pVDZ level of theory. Furthermore, a comparison of the stabilization energies per C atom of the isomeric systems of PAHs shows that the fused acene-azulenes systems (8-9 kcal mol À1 ) are comparable in stability with the polyazulenes (8-9 kcal mol À1 ).…”

“…But both of these systems are somewhat less stable than the acene-azulene systems that have already been synthesized (10-11 kcal mol À1 ), such as 7-5-6 and 7-5-6-6 moieties. 51 These stabilization energies were calculated with the help of isodesmic reactions of the form,…”

Construction of Polycyclic π‐Conjugated Systems Incorporating an Azulene Unit Following the Oxidation of 1,8‐Diphenyl‐9,10‐bis(phenylethynyl)phenanthrene

“…[5,[27][28][29][30][31] Thus, the embedding of an azulenec ore into alternant PAHs could change both the molecular geometry and the electronicp roperties of the originalP AHs. Despite recenti nterest in the structural and electronic perturbations from the incorporationo fo ne or more azuleneu nit(s)i nto pconjugated systems, [32][33][34] the development of ar elatively simple and efficient method to construct azulene-embedded PAHs remains av ery challenging issue due to the limited number of synthetic methodologies.…”

Diazuleno‐s‐indacene Diradicaloids: Syntheses, Properties, and Local (anti)Aromaticity Shift from Neutral to Dicationic State

“…[1] However,l arge-sized acenes with desirable electronic properties are intrinsically reactive. [4] Then ew p-conjugated systems usually display very different electronic properties from the acenes.F or example,the 6-5-6-5-6 fused dibenzo-s-indacenes are analogues of pentacene,b ut they show anti-aromaticity and open-shell diradical character depending on the fusion mode. Alternatively,c hemists are looking into acene-like structures in which one or more six-membered benzenoid rings are replaced by non-benzenoid five-and seven-membered rings.…”

“…Alternatively,c hemists are looking into acene-like structures in which one or more six-membered benzenoid rings are replaced by non-benzenoid five-and seven-membered rings. [4] Then ew p-conjugated systems usually display very different electronic properties from the acenes.F or example,the 6-5-6-5-6 fused dibenzo-s-indacenes are analogues of pentacene,b ut they show anti-aromaticity and open-shell diradical character depending on the fusion mode. [5] Azulene,anon-alternant and non-benzenoid bicyclic hydrocarbon, is a1 0 p-electron isomer of naphthalene.I th as ad ipole moment of about 1.08 Db ecause of intramolecular donor (five-membered ring) and acceptor (seven-membered ring) interactions,a nd possesses unique physicochemical properties currently unattainable by benzenoid systems.…”