Solid-State Reversible Dual Fluorescent Switches for Multimodality Optical Memory

Abstract

Fluorescent photoswitches are highly attractive, because they hold great promises for photonic devices and imaging. However, a limited number of reversible switches with a response to light have been achieved in the solid state. Here, we report reversible dual fluorescent photoswitching characteristics in the solid state of spiropyran (SP)−functionalized tetraphenylethene (TPE) derivatives. These photoswitches exhibit two distinct and selectively addressable states, a cyan fluorescence and a red fluorescence, which can be conveyed into each other in a reversible feature upon irradiation with alternating UV and visible light. Detailed spectroscopic and theoretical studies suggest that the nonplanar molecular conformation of TPE moieties leads to large free volumes, which facilitates the reversible photoisomerization of SP. The excellent reversibility and high-contrast fluorescence of solid-state photoswitches enable great applications in multimodality anticounterfeiting and optical writing and erasing fluorescent devices.

Organic molecular aggregates: From aggregation structure to emission property

“…Similarly, Yang and coworkers presented two unique examples of photoresponsive materials (TPEA‐SP and TPEB‐SP) with reversible dual fluorescence switches in solid states. [ 88 ] SP can perform reversible photoisomerization between the closed state and the MC open form under the stimuli of UV and visible irradiation. The experimental and theoretical calculation results show that under UV light, the intramolecular energy transfer from TPE to MC moiety can take place, which leads to the transformation of the fluorescence between bright cyan and red.…”

Reversible Three‐Color Fluorescence Switching of an Organic Molecule in the Solid State via “Pump–Trigger” Optical Manipulation

“…It is noteworthy that the single molecules of BOSA‐SP and BOSA‐MC occupied volumes of 66.35±0.003 and 65.30±0.002, respectively. Compared with the reported high volume of the SP (69.00±0.21) and MC (67.60±0.26) moieties, [2c] there was a significant reduction in the volume occupied by SP and its photoisomers (MC) after the twisted BOSA moiety was connected, which suggests that this connection created a large intermolecular space; the twisted BOSA moiety increased the intermolecular distance of the MC and SP moieties in the solid state, which enabled the “trigger” light to induce reversible reversion between MC and SP in the solid state.…”

“…Detailed time‐dependent spectroscopy studies showed that under continuous UV‐light irradiation, the intensity of the new absorption (576 nm) and emission peaks (692 nm) gradually intensified, and the emission peak centered at 532 nm gradually declined (Figures 1c and d). These results indicate that UV light successfully triggered the switch from BOSA‐SP to BOSA‐MC in the solid state (Figure 1a) [2b,c] . And the absorbance of BOSA‐MC solid film dropped less after 48 hours of non‐stop testing in a dark environment (Figure S2).…”

“…These observations suggest that intramolecular energy transfer from BOSA to MC in BOSA‐MC plausibly occurred, [2b, 17] which possibly induced the fluorescence switching of BOSA‐SP under irradiation with the “trigger” light. Analysis of the fluorescence lifetime showed that after the MC moiety was connected to BOSA, the fluorescence lifetime of BOSA decreased from 2.13 ns to 1.35 ns, which further suggests that intramolecular energy transfer occurred (Figure S13) [2c, 14a] . The NTO calculations for BOSA‐MC show that the hole and particle involved in the S 1 →S 0 transition in BOSA‐MC were localized on the BOSA moiety, while they were localized on the MC moiety for the S 2 →S 0 transition (Figures 3 and S14), which indicate that the green (weak) and red fluorescence of BOSA‐MC came from the BOSA and MC moieties, respectively [15b] .…”

“…Figure S15 shows that there were no obvious diffraction peaks in the XRD patterns of the powders in the different states, which means that the powdered BOSA‐SP remained amorphous before and after it was triggered with UV light. To further explore the molecular conformation and packing of BOSA‐SP in the aggregated state, molecular dynamics simulations were performed to predict molecular packing in the solid state [2c, 18] . Figure S16a shows that BOSA‐SP and BOSA‐MC adopted a twisted molecular configuration and loose packing in the aggregated state, accounting for their amorphous structure.…”