Nile Red and Nile Blue: Applications and Syntheses of Structural Analogues

Abstract

Nile red and Nile blue are highly fluorescent and photostable organic dyes from the benzo[a]phenoxazine family. They have been used as histological stains for imaging lysosomes and lipids in vitro. The dyes' high quantum yields and solvent-dependent optical properties make them ideal scaffolds for the development of pH probes and local polarity indicators. Reviews of the literature in this area are scarce with only one review ever published in 2006. It has been 10 years since and the field has evolved. This review aims to expand upon topics covered by the previous reviewers and to report on recent advances in the literature. As authors, we hope to convey a sense of scope and to spark renewed interest in this useful niche of dye chemistry.

Tunable Supramolecular Assembly and Photoswitchable Conversion of Cyclodextrin/Diphenylalanine‐Based 1D and 2D Nanostructures

“…[20] As shown in Figure 4a,N ile Red barely fluoresced in aqueous solution, while it greatly increased upon combination with nano-assemblies.I nterestingly,the fluorescence intensity of Nile Red loaded with 2Dnanosheets was much stronger than with nanotubes.T he fluorescence lifetimes and quantum yields of Nile Red-loaded nanosheets were quite similar to those of Nile Red-loaded nanotubes ( Figure S29), indicating that the hydrophilicity of the environment of the absorbed Nile Red was similar in the 1D and 2D structures.T herefore,apossible explanation regarding the stronger fluorescence of the 2D-nanosheet/Nile Red system is that, since H-cis was more polar owing to the dipole formed upon switching,lower amounts of H and Ada-FF were involved in the assembly formation when H was in its cis state.T his would lead to less absorption and/or more selfquenching of the dye as ar esult of denser packing. [20] As shown in Figure 4a,N ile Red barely fluoresced in aqueous solution, while it greatly increased upon combination with nano-assemblies.I nterestingly,the fluorescence intensity of Nile Red loaded with 2Dnanosheets was much stronger than with nanotubes.T he fluorescence lifetimes and quantum yields of Nile Red-loaded nanosheets were quite similar to those of Nile Red-loaded nanotubes ( Figure S29), indicating that the hydrophilicity of the environment of the absorbed Nile Red was similar in the 1D and 2D structures.T herefore,apossible explanation regarding the stronger fluorescence of the 2D-nanosheet/Nile Red system is that, since H-cis was more polar owing to the dipole formed upon switching,lower amounts of H and Ada-FF were involved in the assembly formation when H was in its cis state.T his would lead to less absorption and/or more selfquenching of the dye as ar esult of denser packing.…”

“…We have established that the 2D nanosheets and 1D nanotubes constructed from Ada-FF and H could intercon-vert with perfect reversibility.W ed ecided to investigate the absorption and fluorescence enhancement behaviors of these 1D-and 2D-nano-assemblies using Nile Red, aw ell-established polarity-sensing dye. [20] As shown in Figure 4a,N ile Red barely fluoresced in aqueous solution, while it greatly increased upon combination with nano-assemblies.I nterestingly,the fluorescence intensity of Nile Red loaded with 2Dnanosheets was much stronger than with nanotubes.T he fluorescence lifetimes and quantum yields of Nile Red-loaded nanosheets were quite similar to those of Nile Red-loaded nanotubes ( Figure S29), indicating that the hydrophilicity of the environment of the absorbed Nile Red was similar in the 1D and 2D structures.T herefore,apossible explanation regarding the stronger fluorescence of the 2D-nanosheet/Nile Red system is that, since H-cis was more polar owing to the…”

A Polyaromatic Gemini Amphiphile That Assembles into a Well‐Defined Aromatic Micelle with Higher Stability and Host Functions

“…To compare the host capability between aromatic micelles 3 and 4,N ile red (NR)a nd methyl-capped resorufin were initially employed as at ypical solvatochromic dye [15] and its reference compound with the same core structure,r espectively.R ed solid NR was manually ground with amphiphile 1 or 2 in a1:1 molar ratio for 5min using asmall-sized agate mortar and pestle,a nd the resultant solids were mixed with H 2 Oa tr oom temperature (Figure 5a). [10,16] Removal of suspended, hydrophobic NR by centrifugation and filtration afforded clear aqueous solutions of host-guest composites 3·(NR) n (n % 5) and 4·(NR) n (n % 2).…”

A Polyaromatic Gemini Amphiphile That Assembles into a Well‐Defined Aromatic Micelle with Higher Stability and Host Functions

“…To compare the host capability between aromatic micelles 3 and 4,N ile red (NR)a nd methyl-capped resorufin were initially employed as at ypical solvatochromic dye [15] and its reference compound with the same core structure,r espectively.R ed solid NR was manually ground with amphiphile 1 or 2 in a1:1 molar ratio for 5min using asmall-sized agate mortar and pestle,a nd the resultant solids were mixed with H 2 Oa tr oom temperature (Figure 5a). [10,16] Removal of suspended, hydrophobic NR by centrifugation and filtration afforded clear aqueous solutions of host-guest composites 3·(NR) n (n % 5) and 4·(NR) n (n % 2).…”