Luminescent Behavior Elucidation of a Disilane‐Bridged D–A–D Triad Composed of Phenothiazine and Thienopyrazine

Abstract

A s-p extended aryldisilane,c omprising at hienopyrazine group as an acceptor fragment and phenothiazine groups as the donor moiety,h as been prepared through the introduction of two Si À Si bridges (compound 1). X-ray diffraction analysis determined the crystal structure of 1,a nd experimental and theoretical approaches investigated its optical properties.S olvatochromic studies revealed the dual emission of 1 in all solvents tested. Compound 1 also exhibited fluorescence in the solid state upon excitation with ahand-held UV lamp,a sw ell as mechanochromic luminescent properties. The packing mode in the crystal structure,v ariation of phenothiazine conformation, morphological changes between crystalline and amorphous phases are the major factors showing reversible fluorescence under external stimuli. A theoretical conformer study found that 1 exists in distinct conformational groups differing in Gibbs free energy by less than 3kcal mol À1 .T he conformer in the crystalline state of 1 can promote the complete separation of the HOMO and LUMO between the phenothiazine donor and the thienopyrazine acceptor,l inked by the disilane linker.H OMO-LUMO energy transition in the crystalline state is forbidden due to the lacko ff rontier orbital overlap.C rystalline state emission showed LUMO ! HOMOÀ1transition (locally excited (LE) state). In the amorphous state,t he partial presence of quasiaxial conformers allows intramolecular charge-transfer type emission via energy transfer from dominant quasi-equatorial conformers.T he strategy proposed in this work provides important guidance for developing stimuli-responsive materials with controlled excited states.

Luminescent Behavior Elucidation of a Disilane‐Bridged D–A–D Triad Composed of Phenothiazine and Thienopyrazine

“…Single crystals of 1 suitable for X-ray diffraction (XRD) analysis were obtained by slow evaporation of n-pentane solution. [15] Thec rystal structure is depicted in Figures 2a nd S1. Compound 1 has aq uasi-equatorial phenothiazine structure.T he disilane bonds are in a syn conformation to thienopyrazine,a nd the entire molecule has an M-shaped structure.T he highly distorted geometries between phenothiazine and phenyl rings (C12-N1-C13-C14 = 83.7(4)8 8) could contribute to the effective spatial separation of the HOMO and LUMO (vide infra).…”

Construction of Mechanofluorochromic and Aggregation‐Induced Emission Materials Based on 4‐Substituted Isoquinoline Derivatives

“…Organic mechanofluorochromic (MFC) materials are a kind of important smart fluorescence materials, which exhibit the changes of fluorescent colors under the stimulation of external pressure, have received extensive attention due to the application in solid‐state fluorescent sensors, anti‐counterfeiting materials, and optical recording [1–15] . In early studies, the discovery of such materials was mostly based on chance, [1] in fact, although many organic MFC materials have been reported till now, the design strategy and formation mechanism are still unclear.…”

“…Organic mechanofluorochromic (MFC) materials are a kind of important smart fluorescence materials, which exhibit the changes of fluorescent colors under the stimulation of external pressure, have received extensive attention due to the application in solid-state fluorescent sensors, anti-counterfeiting materials, and optical recording. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] In early studies, the discovery of such materials was mostly based on chance, [1] in fact, although many organic MFC materials have been reported till now, the design strategy and formation mechanism are still unclear. Generally speaking, it is believed that an organic molecule with twisted molecular conformation and capable of emitting solid-state fluorescence is a potential candidate for MFC molecules, because the twisted conformation is easy to lead to loose stacking mode and thus a morphological change under the stimulation of external pressure, resulting in the change of solid-state fluorescence color.…”

Thermally Activated and Aggregation‐Regulated Excitonic Coupling Enable Emissive High‐Lying Triplet Excitons**

“…[17] We hypothesized that it may be possible to achieve RTP from higher-lying triplet states by accessing non-equilibrium conformers in the excited state in the solid state, where the interconversion barrier from one conformer to another must be overcome for excitonic coupling to occur. Based on this concept, we report two conjugated RTP molecules, PXZ-Nap and PTZ-Nap (Figure 1d) using phenoxazine (PXZ) and phenothiazine (PTZ) as donors, which have both been observed to show conformational dynamics under external stimuli, [18] and a substituted naphthalene (Nap) as the acceptor. The decoration of a 10H-phenothiazine-5,5-dioxide unit on the Nap distal to the donor is anticipated to modulate the excited state dynamics and to accelerate the ISC process owing to the presence of the sulfur atom.…”