Effect of Substitution Pattern of tert‐Butyl Groups in a Bisbenzofuropyrazine Core π‐System on Optical Properties: Unique Mechanochromic Fluorescence Behavior

Abstract

Bisbenzofuro[2,3‐b : 2′,3′‐e]pyrazine (BBFPy) and its 2,8‐ and 3,9‐di(tert‐butyl)‐substituted derivatives (2 a and 2 b) were synthesized by palladium‐catalyzed intramolecular direct arylation as the key step. The effect of introduction of two tert‐butyl groups to the BBFPy core at the different positions on the fluorescent properties was then investigated. The tert‐butyl groups not only enhance the tractability with increasing solubility, but also induce different crystal‐packing patterns as anticipated. The compounds 2 a and 2 b show relatively strong blue fluorescence in both the solution and solid state. The 2,8‐isomer 2 a specifically exhibits a unique mechanochromism in the solid state; 2 a exhibits two crystalline forms, both of which show green fluorescence by grinding, while different self‐recovering fluorescence patterns between them are observed by standing. The intriguing mechanochromism is rationally interpreted in terms of molecular arrangements determined by X‐ray crystallography.

MnO2-Mediated Oxidative Cyclization of “Formal” Schiff’s Bases: Easy Access to Diverse Naphthofuro-Annulated Triazines

“…The first synthetic approach comprises the annulation of the heterocyclic ring to a benzofuran core ( Scheme 1 a) [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. Alternatively, other approaches include the intramolecular cyclization (C-C bond formation) of arylhetaryl ethers [ 35 , 36 , 37 , 38 , 39 , 40 ] ( Scheme 1 b) or the intramolecular cyclization (C-O bond formation) of 2-hetaryl-substituted phenol derivatives [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ] ( Scheme 1 c), as well as the intermolecular tandem C-C/C-O cross-coupling reaction of prefunctionalized substrate [ 48 , 49 , 50 ] to form a furan ring fused between the benzene and mono/diazine ring. However, these approaches usually require multistep synthesis, harsh reaction conditions, and the use of transition metal catalysts or special reagents and conditions.…”

Stimuli‐Responsive Properties on a Bisbenzofuropyrazine Core: Mechanochromism and Concentration‐Controlled Vapochromism

“…To investigate the luminescence properties in the aggregation state, each molecule was recrystallized using various methods and conditions. The previously reported linear‐type bis(benzofuro)[2,3‐ b :2′,3′‐ e ]pyrazine without any substituents (R=H in Linear‐R , Figure 1) was too insoluble to be recrystallized [10] . However, the bent‐type Bent‐H was soluble in various organic solvents even without side chains.…”

“…Recently, we have synthesized several thermally stable bisbenzofuro[2,3‐ b :2′,3′‐ e ]pyrazine derivatives by the palladium‐catalyzed intramolecular double cyclization (Figure 1, Linear‐R ) [10] . In particular, 2,8‐di‐ tert ‐butyl‐bisbenzofuro[2,3‐ b :2′,3′‐ e ]pyrazine formed two different crystal polymorphs and exhibited self‐healing mechanochromic properties.…”

“…[9] Recently, we have synthesized several thermally stable bisbenzofuro [2,3-b:2',3'-e]pyrazine derivatives by the palladiumcatalyzed intramolecular double cyclization (Figure 1, Linear-R). [10] In particular, 2,8-di-tert-butyl-bisbenzofuro [2,3-b:2',3'e]pyrazine formed two different crystal polymorphs and exhibited self-healing mechanochromic properties. Moreover, their bent-type isomers, bis(benzofuro) [2,3-b:3',2'-e]pyrazines (Bent-R), were also synthesized, and parent unsubstituted bis(benzofuro) [2,3-b:3',2'-e]pyrazine (Bent-H) was found to be a good phosphorescent emitter in a dispersed state.…”

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

“…This method is straightforward and highly step-economical, enabling us to produce condensed (hetero)acenes from rather simple polyarenes, in which several aromatic units are connected with each other through appropriate linker units [2][3][4][5][6][7][8][9][10][11]. Recently, we reported the synthesis and optical properties of a series of furan-fused aromatics via the formal dehydrogenative coupling adopting oxygen atom as the linker [12][13][14][15][16][17]. In particular, bisbenzofuro [2,3- were found to exhibit intense photoluminescence with relatively high quantum efficiency (Φ flu up to 0.70), indicating that the BBFZPy scaffold may serve as a key fluorophore unit in certain light-emitting functional materials (Scheme 1) [14].…”