Donor–Acceptor–Donor Thienopyrazines via Pd-Catalyzed C–H Activation as NIR Fluorescent Materials

Abstract

A series of thienopyrazine-based donor–acceptor–donor (D–A–D) near-infrared (NIR) fluorescent compounds were synthesized through a rapid, palladium-catalyzed C–H activation route. The dyes were studied through computational analysis, electrochemical properties analysis, and characterization of their photophysical properties. Large Stokes shifts of approximately 175 nm were observed, which led to near-infrared emission. Computational evaluation shows that the origin of this large Stokes shift is a significant molecular reorganization particularly about the D–A bond. The series exhibits quantum yields of up to φ = >4%, with emission maxima ranging from 725 to 820 nm. The emission is strong in solution, in thin films, and also in isolation at the single-molecule level. Their stable emission at the single-molecule level makes these compounds good candidates for single-molecule photon sources in the near-infrared.

N‐Ethyl Carbazole Derived D‐π‐A‐π‐D Based Fluorophores: Consolidated Spectroscopic, Viscosity and DFT Studies

“…Hence, the absorption and emission bands for the fluorophores follows the order 5 c > 5 b > 5 a , whereas the Stokes shifts are in order 5 b > 5 a > 5 c . Among the fluorophores, 5 b possesses the largest Stokes shift, which apparently undergoes a major structural reformation in the excited state due to ICT from D 2 donor to dicyano vinylene unit …”

Effect of Donor Strength and Bulk on Thieno[3,4‐b]‐pyrazine‐Based Panchromatic Dyes in Dye‐Sensitized Solar Cells

“…Ferrocene was used as a reference standard, taken as 0.70 V vs. NHE in DCM and oxidation potentials are reported versus normal hydrogen electrode (NHE, Table ). 2,3‐Diethylthieno[3,4‐b]pyrazine, and 4‐bromo‐ N , N ‐bis(4‐hexyloxyphenyl)aniline (TPA‐Br) were prepared according to literature precedent . 7‐Bromo‐4‐( p ‐tolyl)‐1,2,3,3a,4,8b‐hexahydrocyclopenta[b]indole (Ind‐Br) was prepared according to literature precedent .…”

Modern Synthetic Avenues for the Preparation of Functional Fluorophores

“…C−H activation has also been successfully employed for the functionalization of other heterocycles, as exemplified in the recent work of Delcamp, Hammer, and co‐workers 25. Fluorescent thienopyrazine‐based donor–acceptor–donor compounds were prepared by double C−H arylation of the thiophene moiety.…”