Structure-Directed Functional Properties of Phenothiazine Brominated Dyes: Morphology and Photophysical and Electrochemical Properties

Abstract

A series of nine dyes based on electron-donating phenothiazine core functionalized with various carbonyl containing electron-withdrawing moieties as primary end group and with or without bromine as a second heavy end group were designed and synthesized to generate variable supramolecular architectures with distinct thermotropic, photophysical, and electrochemical properties. The supramolecular architecture of the obtained dyes was studied in detail by single crystal X-ray diffraction and polarized light microscopy, while optoelectronic properties were investigated by UV–vis and photoluminescence spectroscopy and cyclic voltammetry measurements. The phenothiazine dyes emit light from UV to orange domain, depending on the electron-withdrawing substituent, with great quantum yield reaching up to 71% and high color purity. The introduction of the bromine as a second substituent produced a nearly 2-fold increase of the quantum yield, compared with their counterparts. It was settled that this major benefit of the bromine on the improvement of the quantum yield happened because by its presence some molecular orbital interactions were generated. An interesting and challenging achievement was evidenced in the case of the direct connection of the formyl group to the phenothiazine ring when an unexpected planarization of the dye, unknown up to now in the literature, with drastic consequences on the photophysical and electrochemical behavior was attained. It was concluded that there is a close relationship between the nature of the building blocks of the phenothiazine dyes and their ability to promote favorable properties for different optoelectronic applications.

Electron‐Rich Phenothiazine Congeners and Beyond: Synthesis and Electronic Properties of Isomeric Dithieno[1,4]thiazines

“…All dithieno[1,4]thiazines 2 as well as phenothiazine 1 fluoresce weakly in dichloromethane solutions (Table ; for absorption and emission spectra plots, see the Supporting Information Chapter 5). For illustration, the fluorescence quantum yield Φ f of anti ‐ anti dithieno[1,4]thiazine 2 d in dichloromethane is 0.03, which matches with analogous phenothiazines . In accordance with phenothiazines, 2 d planarizes after photoexcitation to the vibrationally relaxed excited S 1 state, which rationalizes the relatively large Stokes shift (Figure ).…”

“…For illustration, the fluorescence quantum yield F f of anti-anti dithieno[1,4]thiazine 2d in dichlorome-thane is 0.03, [25,26] whichm atches with analogousp henothiazines. [27] In accordance with phenothiazines, [28] 2d planarizes after photoexcitation to the vibrationally relaxede xcited S 1 state, which rationalizes the relativelyl arge Stokes shift (Figure 8).…”

Bis[1]benzothieno[1,4]thiazines: Planarity, Enhanced Redox Activity and Luminescence by Thieno‐Expansion of Phenothiazine

“…The anti-anti BBTTs 7 easily surpassed similars ubstituted phenothiazines in terms of fluorescence quantum yields. [29] In the emission data (l max,em and fluorescenceq uantum yields F F ), no major influence of the corresponding para-substituentsw as found. Time-dependent DFT (TD-DFT) calculations were performed to explore the electronic nature of the vibrationally relaxed first excited state of anti-anti BBTT 7c (Figure 7).…”

“…Anellated 1,4‐thiazines, such as phenothiazine without any additional functionalization of the anellated π‐system, normally reached only negligible fluorescence quantum yields, whereas the dithieno[1,4]thiazine was essentially not luminescent. The anti ‐ anti BBTTs 7 easily surpassed similar substituted phenothiazines in terms of fluorescence quantum yields …”

Dithieno[1,4]thiazines and Bis[1]benzothieno[1,4]thiazines—Organometallic Synthesis and Functionalization of Electron Density Enriched Congeners of Phenothiazine

“…In contrast, the oxidation potential of the exo-exo isomer 2f-a is more anodically shifted than for 2a-i because of a less efficient delocalization of the π-electron density. Whereas the syn-syn isomers 2a fluoresce very weakly [35], which is atypical for comparable phenothiazines [43], the anti-anti isomer 2e-a fluoresces rather phenothiazine-like [30].…”