Metal‐Free Facile Synthesis of Multisubstituted 1‐Aminoisoquinoline Derivatives with Dual‐State Emissions

Abstract

Although isoquinoline is a good traditional fluorescent structural unit, most of its derivatives emit fluorescence in solution and a few of them can emit solidstate fluorescence as well. Herein, a series of multisubstituted 1-aminoisoquinoline derivatives were synthesized by a simple reaction of a readily available 4H-pyran derivative and secondary amines. The reaction had advantages of metalfree, mild conditions, simple operation, and good yields, which was realized by a ring-opening and sequential ringclosing mechanism. These 1-aminoisoquinoline derivatives were found to exhibit interesting dual-state emissions. In the solution, they emitted strong blue fluorescence at about 458 nm. In the solid state, they emitted solid-state blue fluorescence at 444-468 nm with high fluorescence quantum yields of 40.3-98.1%. Crystal structural analyses indicated that solid-state emissions of these compounds originated from twisted molecular conformations and the resultant loose stacking arrangements. Furthermore, their solid-state fluorescence wavelengths were demonstrated to depend on molecular conformations rather than stacking arrangements. The discovery of these 1-aminoisoquinolines with multiple reaction sites provides new possibilities for the development of solid-state fluorescent materials based on the traditional isoquinoline skeleton.

Rational Design and Facile Synthesis of Dual‐State Emission Fluorophores: Expanding Functionality for the Sensitive Detection of Nitroaromatic Compounds

“…This phenomenon may be related to their different twisted molecular conformations and stacking arrangements. [57] Furthermore, the CIE 1931 chromaticity coordinates of compounds 4 a-4 f also apparently illustrate this difference of fluorescence between solution (Figure 3c) and solid state (Figure 3d). Optical properties of all fluorophores in the dual-state are listed in Table S9.…”

“…Compared with the fluorescence in solution (the maximum emission peak of 4 a – 4 e in THF locating at 427, 430, 445, 442, 418 and 377 nm, respectively), there is a red‐shift within 30 to 80 nm for their maximum emission peak in solid state (locating at 463, 485, 482, 521, 449 and 449 nm, respectively). This phenomenon may be related to their different twisted molecular conformations and stacking arrangements [57] …”

Stacking-dependent tetracolour luminescence and mechanofluorochromic properties of an isoquinoline derivative with aggregation-induced emission

“…The intermediate PIQ can be easily synthesized from 2-(2,6dimethyl-4H-pyran-4-ylidene)-3-oxopentanedinitrile and piperidine by ring-opening and then sequential ring-closing reactions according to our previous report (Scheme S1, ESI †). 31,32 Then PIQ undergoes a three-step procedure to afford the target compound IEPA. The detailed experimental methods and the corresponding characterization are provided in the ESI.…”

“…1A). Herein, the multisubstituted 1-aminoisoquinoline skeleton can ensure the twisted conformation and loose stacking arrangement of the molecule and thus solid-state emission, 31 and ethyl (E)-2-cyano-3phenylacrylate is also beneficial to endow the molecule with aggregation-induced emission (AIE) characteristics. 25 Furthermore, the introduction of (E)-2-cyano-3-phenylacrylate provides a cyano group, ethylene bond, carbonyl group, and phenyl ring, which lead to more possibilities for the formation of weak interactions, such as C-HÁ Á ÁN, C-HÁ Á ÁO, C-HÁ Á Áp, and p-p stacking, and thus might afford more polymorphs through the delicate balance of a variety of non-covalent interactions.…”

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

“…Recently, our group reported the synthesis of a series of multisubstituted 1-aminoisoquinolines (AIQ, Scheme 1) by an efficient and convenient method from a simple 4H-pyran derivative and secondary amines. [38] These compounds emit strong blue fluorescence in solid state with fluorescence quantum yields (Φ F ) of 40-98% due to twisted molecular conformations. But unfortunately, according to our previous report, the AIQ compound does not show MFC activity when the substituent at 1-position is piperidin-1-yl, because its crystalline structure is hard to be destroyed due to excellent crystallization ability.…”