Synthesis, Electronic, and Electro‐Optical Properties of Emissive Solvatochromic Phenothiazinyl Merocyanine Dyes

Abstract

Phenothiazinyl merocyanine dyes with variable substitution patterns on the peripheral benzene ring were synthesized in good yields by Knoevenagel condensation of the corresponding phenothiazinyl aldehydes and N-methylrhodanine or indan-1,3-dione. The electronic properties were investigated by cyclic voltammetry, absorption, electro-optical absorption, and emission spectroscopy. All these merocyanines reveal reversible redox behavior that stems from the phenothiazinyl-centered oxidation to give stable radical cations. The redox potentials strongly correlate with Hammett σ(p) parameters. All merocyanines reveal large Stokes shifts. They also display a pronounced emissive solvatochromism, which is caused by large dipole moment changes upon excitation from the ground to the excited state. These findings are supported by solvatochromism studies and time-dependent DFT computations.

Thiophene-forming one-pot synthesis of three thienyl-bridged oligophenothiazines and their electronic properties

“…2), which are typical for oligophenothiazines [45]. However, the lack of a systematic trend with the numbers of phenothiazinyl units indicates that the excited state property is strongly affected by local conformational biases arising from the planarization of electronic ground state butterfly conformation of phenothiazines in the excited state [57,79]. Also the fluorescence quantum yields Φ f with 15 to 18% essentially remain constant within this series, although, the increasing number of sulfur-containing heterocycles suggests an increase in fluorescence deactivating spin–orbit coupling.…”

“…Over the past one and a half decades the synthetic and physical organic chemistry of oligophenothiazines have been intensively studied in linear [45] and cyclic [46] topologies, as diphenothiazinyl dumbbells brigded by heterocycles [47–49], and as acceptor [50–51], ferrocenyl [52], and alkynyl [53–55] substituted (oligo)phenothiazines. Their pronounced reversible oxidation potentials, their electro- and photochromicity [56], and their luminescence [57–58] have rendered (oligo)phenothiazines interesting candidates as donors in donor–acceptor conjugates with photo-induced electron-transfer characteristics [59–63], as hole-transport materials [64], for applications in mesoporous organo silica hybrid materials [65], and as chromophores in dye-sensitized solar cells [66–68]. Furthermore, (oligo)phenothiazines in their native reduced forms display a pronounced ability to form self-assembled monolayers on gold [69–71] as well as on zinc and iron oxide surfaces [72].…”

Significant improvement of phenothiazine organic dye-sensitized solar cell performance using dithiafulvenyl unit as additional donor

“…Toluene was distilled from sodium benzophenone ketyl under nitrogen immediately prior to use. The starting materials 10-hexyl-10H-phenothiazine-3,7-dicarbaldehyde [47], 4,5-bis(methylthio)-1,3-dithiol-2-one [48] and 4,5-bis(hexylthio)-1,3-dithiol-2-one [48] were synthesized according to the corresponding literature method. All other solvents and chemicals were purchased commercially, and used as received without further purification.…”

Macrocycles embedding phenothiazine or similar nitrogen and/or sulphur containing heterocycles

“…The access to cyclophanes 13 and 15 was possible after reduction with H 2 (Pd/C; 85 and 80 %) of the corresponding cyclophanes with double bonds (Schemes 5, 6) [51]. The syntheses of dialdehydes 22 and 23 were described along with the synthesis of cyclophanes [51,52], but some other procedures to access the 3,7-diformyl or 3,7-diformylthiazinyl phenothiazines were also recently reported [53,54].…”