Stable Red‐Emissive Cationic Dithienotropylium Dyes

Abstract

A series of thiophene-fused tropylium ions, containing various electron-donating amino groups at the terminal positions, was synthesized. The fusion of the thiophene rings, as well as the presence of the terminal amino groups endows the cationic tropylium ion with excellent stability and high pK values. X-ray crystallographic analysis of these compounds revealed a pronounced quinoidal character for the amino-substituted dithienotropylium skeletons. These compounds exhibit attractive photophysical properties such as strong absorption in the visible region combined with red fluorescence. Theoretical calculations suggested that the 3,3'-bithiophene substructure should be crucial for attaining these photophysical properties.

Optical Nature of Non-Substituted Triphenylmethyl Cation: Crystalline State Emission, Thermochromism, and Phosphorescence

“…This finding was confirmed by inspection of the solid-state diffuse reflectance spectra of these crystals (Figure S2). Although several aromatic cations containing heteroatoms such as N or O are known to exhibit intense emission, [37,38] those composed of only hydrogen and carbon exhibit very weak or no emission in solution owing to the favorability of nonradiative decay processes. [39] In fact, the trityl cation in solution displays no emission.…”

Optical Nature of Non-Substituted Triphenylmethyl Cation: Crystalline State Emission, Thermochromism, and Phosphorescence

“…This finding was also confirmed by inspection of the solid-state diffuse reflectance spectra of these crystals (Figure S2). Although several aromatic cations containing heteroatoms such as N or O are known to exhibit intense emission, [37,38] those composed of only hydrogen and carbon exhibit very weak or no emission in solution owing to the favorability of nonradiative decay processes. [39] In fact, the trityl cation in solution displays no emission.…”

Construction of Tricyclic Nitrogen Heterocycles by a Gold(I)‐Catalyzed Cascade Cyclization of Allenynes and Application to Polycyclic π‐Electron Systems

“…Removal of the Hib group from pyrrolonaphthalene 5r bearing an ortho-chlorobenzyl group,followed by palladium-catalyzed intramolecular N-arylation, afforded pentacyclic compound 17 (65 %) and its oxidized form 18 (9 %). To obtain aN -PAC with am ore p-expanded framework, we also investigated using corresponding naphthyl derivative 4s as ak ey precursor in the synthesis.C oppercatalyzed double-bond isomerization of fused indole 4sto the corresponding naphthalene 5s and successive deprotection of the Hib group,f ollowed by palladium-catalyzed intramolecular N-arylation, led to hexacyclic compound 20.F inally, treatment of 20 with triphenylmethylium tetrafluoroborate [25] gave indolium salt 21.N otably,c ompound 21 exhibited sufficient stability that enabled handling under ambient conditions without any precautions.…”