Synthesis and Electronic Properties of Alkynylated Phenothiazines

Abstract

Alkynylated phenothiazines 1, 2, 5, 7, and 12−15 can be synthesized in moderate to excellent yields by sequences of aldehyde−alkyne transformations and/or Sonogashira crosscoupling reactions from suitable phenothiazine aldehydes or bromides. The electronic properties of (hetero)aryl ethynylsubstituted N-methyl-phenothiazines (UV/Vis absorption, fluorescence, redox potentials) strongly correlate with Hammett σ P parameters and indicate that remote substituents

Harvesting solar energy using conjugated metallopolyyne donors containing electron-rich phenothiazine–oligothiophene moieties

“…The dibromo precursors (L1-2Br and L2-2Br) can be obtained from L0-2Br by successive coupling of 2-thienylmagnesium bromide with the corresponding phenothiazine-based dibromide of the lower generation. Conversion of the dibromide derivatives to their corresponding diethynyl congeners can be readily achieved following the typical organic synthetic protocols for alkynylation of aromatic halides [70,80]. It is worth noting that the purification steps become more tedious in the ligand synthesis as the number of thienyl rings m increases.…”

“…The relevant data are collected in Table 2. From the onset values of oxidation potential (E onset, ox ) and reduction potential (E onset, red ), the HOMO and LUMO levels of the polymers were calculated according to the following equations E HOMO = À(E onset, ox + 4.72) eV and E LUMO = À(E onset, red + 4.72) eV (where the unit of potential is V versus Ag/AgCl) [ the oxidation (p-doping) process of the polymer [66,67,70]. Each of P1ÀP2 shows a quasi-reversible phenothiazinyl oxidation at 0.84 and 0.79 V, respectively, and the oxidation potential is reduced with increasing thienyl chain length m, consistent with the phenomenon that delocalization of the generated phenothiazine radical cations is apparently more favored and stabilized by increased conjugation length [98][99][100][101][102][103][104][105] For P2, two additional anodic waves due to the bithienyl cores also appeared at the more positive potentials peaking at ca.…”

“…Phenothiazine (PTZ) belongs to an important class of tricyclic nitrogen-sulfur heterocycles [56], with a broad spectrum of pharmacological activity [57][58][59][60][61][62][63] Phenothiazine has low and highly reversible first oxidation potentials [64][65][66][67] with pronounced propensities to form stable radical cations. Also, phenothiazine and its derivatives serve as good intramolecular reductive quenchers because they show a facile one electron oxidation, and the PTZ radical cation (PTZ Å+ ) is known to have a strong absorption in the visible region [68][69] This makes the identification of the charge-separated intermediate formed upon electron transfer from PTZ to the 3 MLCT excited state of the chromophore unambiguous [70][71][72][73]. The electron-rich nature of phenothiazine makes it a good electron donor in some studies related to donor-chromophore-acceptor triad for photoinduced charge separation [70][71][72][73] and it is also a good electron donor for reductive quenching [74,75].…”

“…Also, phenothiazine and its derivatives serve as good intramolecular reductive quenchers because they show a facile one electron oxidation, and the PTZ radical cation (PTZ Å+ ) is known to have a strong absorption in the visible region [68][69] This makes the identification of the charge-separated intermediate formed upon electron transfer from PTZ to the 3 MLCT excited state of the chromophore unambiguous [70][71][72][73]. The electron-rich nature of phenothiazine makes it a good electron donor in some studies related to donor-chromophore-acceptor triad for photoinduced charge separation [70][71][72][73] and it is also a good electron donor for reductive quenching [74,75]. As a consequence, these favorable electronic properties of phenothiazines have led to their application as electrophore probes in supramolecular assemblies for photoinduced electron transfer (PET) studies and as electron donor components in various optical and electronic domains [76][77][78][79] The prospect of integrating strongly coupled redox-active phenothiazine fragment into conjugated oligothiophene chains could constitute a new class of spacers in optoelectronically-active metallopolyynes.…”

Synthesis and characterization of polymer electrolytes containing phenothiazine-based click polymers for dye-sensitized solar cell applications

“…3,7-Diazido-10-n-hexyl-10H-phenothiazine (M1), 19 20 2,7-diethynyl-9,9-dihexylfluorene (M3), 21 and diethyl dipropargylmalonate (M4) 22 were synthesized using a slight modification of the method reported in the literature. The mixture was frozen and evacuated three times, which was followed by the addition of CuSO 4 ·5H 2 O (5 mol%) under a flow of N 2 gas.…”