Stimuli‐Responsive Organic Dyes with Tropylium Chromophore

Abstract

Tropylium ions possess an interesting combination of structural stability and chemical reactivity due to its Hückel aromaticity and its positively charged polyene nature, respectively. Herein we exploit the chemical versatility and unique structural properties of the tropylium ion to derive a family of novel push-pull organic dyes with strong absorption in the visible range via simple and practical synthetic protocols. These stable organic dyes are highly stimuli-responsive, as demonstrated by their sensitivity towards solvent, pH change, redox reaction, Lewis base and counterion, which marks them as potentially useful compounds for opto-electronic applications.

4-Ferrocenylphenyl-Substituted Tritylium Dyes with Open and Interlinked C+Ar2Entities: Redox Behavior, Electrochromism, and a Quantitative Study of the Dimerization of Their Neutral Radicals

“…Carbonium ion and free radical chemistry have been intertwined ever since, and this concatenation plays a crucial role in the present work. Up to now, the propeller-shaped triphenylmethylium (tritylium) ion and its many ring-substituted variations remain the best-investigated carbocations in chemistry. − Since those early days, diverse families of aryl-stabilized cationic chromophores including xanthenium dyes such as rhodamines, , triangulenium cations such as TOTA + , − helicenium, and cycloheptatrienylium (e.g., tropylium, 5-phenyl­[ a,d ]­dibenzocycloheptatrienylium) − derivatives as shown in Scheme have been developed and are being continuously explored, mainly because of their intriguing optical and redox properties. These colorful dyes combine high stabilities because of their aromatic Hückel-type resonance structures with versatile and tunable physicochemical properties. , …”

“…These colorful dyes combine high stabilities because of their aromatic Huckel-type resonance structures with versatile and tunable physicochemical properties. 3,14 Appropriately positioned electron-donating substituents, which mitigate the electron demand of the methylium center, further aid in stabilizing tritylium cations. The electronic properties of the tritylium-type frameworks and the attached substituents become particularly manifested in the positions of the prominent electronic absorptions in the visible (vis) region and the half-wave potentials of their reductions to first the corresponding neutral radicals and then their associated carbanions.…”

Trapping of chiral enolates generated by Lewis acid promoted conjugate addition of Grignard reagents to unreactive Michael acceptors by various electrophiles

“…Tropylium derivatives are desired structural motives, such as in stimuli-responsive dyes. 12 The model reaction in DCM afforded the product 3a in a promising 19% yield ( Table 1, entry 1). To improve the solubility of the cation 4, we added a polar additive 1,3dimethylimidazolidin-2-one (DMEU) (entry 2).…”

Rupturing Aromaticity by Periphery Overcrowding

“…1a) as a stable C7-symmetric carbocation. Since Doering and Knox's seminal work 11 on its isolation and structural elucidation, its electronic properties have been exploited in organocatalysis, 12 stimuliresponsive dyes, 13 and redox-active polycyclic aromatic hydrocarbons (PAHs). [14][15][16] Relative to benzene, its larger ring size, increased conformational flexibility, and the smaller angles subtended by its substituents (51.4° c.f.…”