Construction of Energy Transfer Systems within Nanosized Polymer Micelles and their Fluorescence Modulation Properties

Abstract

The nanoparticle-based fluorescence resonance energy transfer (FRET) systems have recently attracted considerable attention due to some of their advantages; however, these systems are structurally more complicated than that of small molecule systems, and the energy transfer behavior for particle systems has been seldom investigated. In this study, we synthesized a series of ABC triblock copolymers that contain hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(styrene) (PS) and photochromic poly(2-(3-(3',3'-dimethyl-6-nitrospiro(indoline-2',2-[2H-1]benzopyran)-1'-yl)propanoylo-xy)ethyl methacrylate) (PSPMA) blocks by using the sequential two-step atom transfer radical polymerization (ATRP). The amphiphilic micelles made from these copolymers can incorporate a hydrophobic fluorescent dye, the nitrobenzoxadiazolyl derivative (NBD), thus forming a water dispersible energy transfer system with the fluorescent dye NBD as the donor and spiropyran moieties as the potential acceptor. The spectral properties of NBD/triblock copolymers with varied PS block lengths and PSPMA block lengths have been investigated; the results indicate that the length of PS block in triblock copolymers can affect the energy transfer efficiency of the micelle-based fluorescence modulation system, the micelles with moderate PS block length are preferable for forming FRET system with higher energy transfer efficiency, and short PSPMA blocks (less than 5 repetition units) are enough for efficient energy transfer.

Photoregulation of α‐Chymotrypsin Activity by Spiropyran‐Based Inhibitors in Solution and Attached to an Optical Fiber

“…Subsequent excitation of this isomer with 532 nm laser (as before) resulted in an enhanced (sixfold) average fluorescence relative to the SP isomer. This is consistent with the fluorescence characteristics of the MC isomer, where this isomer is known to have enhanced fluorescence due to π‐conjugation as reported in literature13, 24, 30 (Figure 6, black, λ em ∼630 nm). Subsequent exposure of the Fiber‐2 d to visible light for 5 min decreased the fluorescence intensity, as expected for a photostationary state enriched in SP isomer.…”

“…Specifically, a sample of 2 d was irradiated with visible light (>400 nm) and the resulting UV–visible (UV/Vis) absorption spectrum was measured as shown in Figure 3 (red). The lack of absorption at 550 nm indicates that the sample consists predominantly of the SP isomer, where the MC isomer typically has strong absorption in this region 24. The solution of 2 d in methanol was then irradiated with UV light (365 nm) for 15 min to induce isomerization to the MC isomer as evidenced by a significant and characteristic increase in absorption at 550 nm (Figure 3 a, blue).…”

Nanoporous frameworks exhibiting multiple stimuli responsiveness

“…An interesting feature of the spiropyran switch is that while its closed-ring, SP isomer is practically non-fluorescent, MC shows an intense red emission 47,48 . Consequently, being able to reversibly photoisomerize under solvent-free conditions, PhotoPAFs showed unique solid-state photoswitchable fluorescence, as shown in Fig.…”

From a Molecular Toolbox to a Toolbox for Photoswitchable Fluorescent Polymeric Nanoparticles

“…In PFPNs, both photoinduced electron transfer (PET) and FRET can turn off the emission of the dyes . However, we do not expect PET mechanism in our systems.…”