Photoswitching of bis-spiropyran using near-infrared excited upconverting nanoparticles

Abstract

Bis-spiropryran molecules were grafted onto the surface of upconverting nanoparticles. Fluorescence resonance energy transfer from the upconverting nanoparticles to the surface bis-spiropyran molecules triggered the transformation of the ring-closed bis-spiropyran to the ring-open bis-merocyanine forms.

An Upconversion Nanoparticle with Orthogonal Emissions Using Dual NIR Excitations for Controlled Two‐Way Photoswitching

“…[5] Among the developed various UCNPs with tailored emission profiles, multicolor UCNPs capable of regulating their emission wavelengths from the UV to visible range in response to external stimuli are garnering much interest recently, as they can offer more dynamic platforms for applications in high resolution bio-imaging, multicolor encoding and photoswitching. [6] However, there are few reports on such multicolor UCNPs. Of them, one typical example is the excitation-responsive UCNP, whose emission can be modulated between spectrally pure visible light and mixed UV/Vis emissions by changing the power density of 980 nm NIR excitation.…”

“…Of them, one typical example is the excitation-responsive UCNP, whose emission can be modulated between spectrally pure visible light and mixed UV/Vis emissions by changing the power density of 980 nm NIR excitation. [6b–d] This unique property of the UNCPs was then successfully applied toward driving important chemical reactions and their subsequent applications such as the two-way photoswitching of dithienylethene, [6b] the reversible control over the reflection of liquid crystals [6c] and modulating the biocatalytic activity of bacteria [6d] . However, the use of high power 980 nm NIR light in such UCNP systems, although advantageous, has been shown to cause severe local heating, which has detrimental effects on both solid-state devices and biological systems.…”

“…It should be noted that the relatively weaker emissions of Tm 3 + in LC than that of Er 3+ in LS may be due to i) the quenching effect of Nd 3+ in LC , [8h] and ii) the non-linear excitation nature of UCNPs whereby the UV emissions from Tm 3+ show a stronger dependence on excitation density than the visible emissions of Er 3+ (a 4 photon vs 3 photon process). [6b] Consequently, decreasing the excitation power density eliminated the Tm 3+ emissions more quickly than those of Er 3+ , and excitations of 40 W·cm −2 or lower led to the selective emissions of Er 3+ in the LS only (Figure 2b, bottom curve). This result demonstrates that the emission of Tm@Er under 980 nm excitation can be easily modulated by regulating the excitation power/wavelength, and that the LS can be selectively excited by utilizing a low excitation power density due to the cooperative effect of the Nd 3+ doping, the photon inert shell and the nonlinear excitation properties of UCNPs, [6b, 6c, 11] as represented (Scheme 1b).…”

“…[6b] Consequently, decreasing the excitation power density eliminated the Tm 3+ emissions more quickly than those of Er 3+ , and excitations of 40 W·cm −2 or lower led to the selective emissions of Er 3+ in the LS only (Figure 2b, bottom curve). This result demonstrates that the emission of Tm@Er under 980 nm excitation can be easily modulated by regulating the excitation power/wavelength, and that the LS can be selectively excited by utilizing a low excitation power density due to the cooperative effect of the Nd 3+ doping, the photon inert shell and the nonlinear excitation properties of UCNPs, [6b, 6c, 11] as represented (Scheme 1b). Accordingly, a hexane solution of these nanoparticles displays two different colored bands, blue and green, under 808 nm and 980 nm excitation, respectively, with excitation power densities of 40 W·cm −2 or lower, revealing the orthogonal excitation-emission property of the Tm@Er UNCPs.…”

Nanophotochromism

“…The photoswitching of near-infrared excited upconversion nanoparticles based on LiYF 4 :Tm,Yb was demonstrated with the use of bis-spiropyran [102].…”