Large Red-Shifted Fluorescent Emission via Intermolecular π–π Stacking in 4-Ethynyl-1,8-naphthalimide-Based Supramolecular Assemblies

Abstract

Two low molecular weight gelators containing 4-ethynyl-1,8-naphthalimide groups with large conjugated structure via different length of alkyl chains were synthesized and fully characterized. The gelation properties, structural character, and fluorescence of the gels were investigated via methods of scanning electron microscopy, X-ray diffraction, and spectral studies. The gelators have high fluorescence quantum yields in both solution and solid state. Interestingly, the wavelength of the fluorescent emission in the reversible sol-gel transition process of the gels has a large red-shift of 80 nm in DMF, which is extremely sparse for 1,8-naphthalimide derivatives in the literature. The intermolecular π-π stacking between naphthalimide is suggested to be the main driving force for the gel formation and fluorescent variation by means of temperature-dependent (1)H NMR study and theoretical calculation.

Steric‐Structure‐Dependent Gel Formation, Hierarchical Structures, Rheological Behavior, and Surface Wettability

“…Given that at emperature of 100 8Ci st he gel-tosol transition point of GO,t he 1 HNMR spectra suggest that weak p-p stacking exists in the gel state. [81,82] The signal assigned to the amide (NH) proton Hc experiencesaslight up-shield shift as the temperature was raised from 40 (d = 8.028 ppm) to 80 8C( d = 8.025 ppm). Additionally,t he signal pattern was furtherb roadened between 100 and 120 8Ca nd Hc was shifted upfieldt os ome extent,w hich indicatedd isruption of the hydrogen bondinga te levated temperatures.…”

Synthesis of Diisocyanate‐Containing Thiophenes and Their Use in PDMS‐Based Segmented Polymers

“…In the solid state, formation of hydrogen bonds and alignment of the bisurea units is possible, leading to an ordering of terthiophenes in distinct hard block segments and thus, phase separation. Consequently, the π system is enhanced resulting in a red shift of the fluorescence emission . With the emission maximum at 635 nm the optical band gap of the polymer film can be calculated to 1.95 eV.…”

The self-assembly of monosubstituted BODIPY and HFBI-RGD

“…34,35 Because of the presence of p-p interactions between molecules, the reduced HOMO-LUMO energy gap resulted in a slight bathochromic shi. 36,37 Thus, a slight red-shi appeared for all these dyes with the increase in concentration. Among the three BODIPY dyes, dye 3b exhibited the best co-planarity; on the one hand, this property limited free rotation, resulting in the least non-radiative energy loss but on the other hand, it greatly contributed to intermolecular p-p aggregation compared to the observations for dye 3a and dye 3c.…”