Crystallization and Aggregation-Induced Emission in a Series of Pyrrolidinylvinylquinoxaline Derivatives

Abstract

Aggregation-induced emission (AIE) has been meanwhile observed for many dye classes and particularly for fluorophores containing propeller-like groups. Herein, we report on the AIE characteristics of a series of four hydrophobic pyrrolidinylvinylquinoxaline (PVQ) derivatives with phenyl, pyrrolyl, indolyl, and methoxythienyl substituents used to systematically vary the torsion angle between this substituent at the quinoxaline C2 position and the planar PVQ moiety. These molecules, which are accessible via four- or five-component one-pot syntheses, were spectroscopically studied in organic solvents and solvent–water mixtures, as dye aggregates, solids, and entrapped in polystyrene particles (PSP). Steady-state and time-resolved fluorescence measurements revealed a strong fluorescence enhancement for all dyes in ethanol–water mixtures of high water content, accompanying the formation of dye aggregates with sizes of a few hundred nm, overcoming polarity and H-bonding-induced fluorescence quenching of the charge-transfer-type emission of these PVQ dyes. The size and shape of these dye aggregates and the size of the AIE effect are controlled by the water content and the substituent-dependent torsion angle that influences the nucleation process and the packing of the molecules during aggregation. Staining of 1 μm-sized carboxy-functionalized PSP with the PVQ dyes resulted also in a considerable increase in the fluorescence quantum yield and lifetime, reflecting the combined influence of the restricted molecular motion and the reduced polarity of the dye microenvironment.

Festkörperemittierende Aroyl‐S,N‐Ketenacetale mit steuerbaren aggregationsinduzierten Emissionseigenschaften

“…Chromophore mit ausgeprägten AIE‐Eigenschaften konnten bereits als Marker für auf Mitochondrien zielende Krebstherapien oder für Krebsablationen und als Nanosonden für tumorspezifisches Bioimaging oder als Biosensoren genutzt werden . AIE‐aktive Fluorophore sind zudem vielversprechende Kandidaten für neuartige Signalverstärkerungsstrategien in Assays oder als verbessertes nanopartikelbasiertes Bioimaging, da solche Farbstoffe eine höhere Farbstoffbeladungsdichte ermöglichen als konventionelle ACQ‐Farbstoffe . Abgesehen von bioanalytischen Anwendungen wurden AIE‐Chromophore ebenfalls für optoelektronische Bauteile genutzt .…”

“…Ein häufig verwendetes Strukturmotiv ist das Tetraphenylethen (TPE) und daraus abgeleitete Derivate, wie auch Anthracen‐ und Carbazol‐basierte Strukturen . In den letzten Jahren konnten wir zeigen, dass auch polare heterocyclische Systeme wie Quinoxaline oder Indolon‐Merocyanine AIE‐aktiv sein können …”

Solid State and Aggregation Induced Emissive Chromophores by Multi‐component Syntheses

“…[42] Steady-state and time-resolved fluorescence measurements displays strong fluorescence enhancement for all dyes in ethanol À water mixtures of high water content. [42] Steady-state and time-resolved fluorescence measurements displays strong fluorescence enhancement for all dyes in ethanol À water mixtures of high water content.…”

“…Just recently, we disclosed systematic spectroscopic studies on four 2-donor substituted 3-(N-pyrrolidinyl)vinylquinoxalines 20 (n = 1, R 1 = phenyl, 1-methylpyrrol-2-yl, 1-methylindol-3-yl, 5-methoxythien-2-yl) in organic solvents and solvent À water mixtures, as dye aggregates, solids, and entrapped in polystyrene particles (PSP). [42] Steady-state and time-resolved fluorescence measurements displays strong fluorescence enhancement for all dyes in ethanol À water mixtures of high water content. Dye aggregates with sizes of a few hundred nm are formed that prevent polarity-and hydrogen bonding-induced fluorescence quenching of the charge-transfer emission.…”

Sequential Cu‐Catalyzed Four‐ and Five‐Component Syntheses of Luminescent 3‐Triazolylquinoxalines

“…By increasingt he electron-donating character of the heterocyclic substituent R 1 ,t he absorption and the emission bands shiftb athochromically from 2-thienyl (3t, l max,abs = 368 nm, l max,em = 541 nm) over 1-methylpyrrolyl (3b, l max,abs = 384 nm, l max,em = 548 nm) to 1-methylindolyl( 3a, l max,abs = 393 nm, l max,em = 541 nm) and p-Me 2 NC 6 H 4 (3s, l max,abs = 393 nm, l max,em = 541 nm, Figure 8). The Stokes shifts vary in a range from 7000 to 8700 cm À1 ,e xcept for the 2-thienyl derivative 3t,w hich is significantly smaller with 4500 cm À1 .T he fluorescence quantum yields F f of the 3-triazolylquinoxalines are relativelys mall compared to 3-aminovinyl derivatives [23] or 3ethynylquinoxalines. [12b, 15] The highest value can be found for the p-Me 2 NC 6 H 4 derivative 3s (Table 2).…”