Abstract
The spectroscopic properties of poly(methyl methacrylate) polymer films doped with two kinds of photochromic molecular switches are investigated. A green-fluorescent sulfonyl diarylethene (P1) is combined with either a non-fluorescent diarylethene (P2) or red-fluorescent spiropyran (P3). Photoswitching between the colorless and colored isomers (P1: o-BTFO4 ↔ c-BTFO4, P2: o-DTE ↔ c-DTE, P3: SP ↔ MC) enables the P1 + P2 and P1 + P3 films to be cycled through three distinct states. From the initial state (o-BTFO4 + o-DTE/SP), irradiation with UV light generates the second state (c-BTFO4 + c-DTE/MC), where c-BTFO4 → c-DTE/MC energy transfer is established. Irradiation with green light then generates the third state (c-BTFO4 + o-DTE/SP), where the energy transfer acceptor is no longer present. Finally, irradiation with blue light regenerates the initial state. For the P1 + P2 film, only one state is fluorescent, with the irradiation inputs required to be entered in the correct order to access this state, acting as a keypad lock. For the P1 + P3 film, the states emit either no fluorescence, red fluorescence, or green fluorescence, all using a common excitation wavelength. Additionally, once the fluorescence is activated with UV light, it undergoes a time-dependent color transition from red to green, due to the pairing of P-type and T-type photochromes. These multi-photochromic systems may be useful for security ink or imaging applications.
Highlights
We examine the spectroscopic properties of photochrome-doped poly(methyl methacrylate) (PMMA) polymer films
Three photochromic molecules are employed in this study (P1, P2, and P3), with their spectroscopic properties examined when they are doped in a PMMA polymer film
P2 is a diarylethene labelled DTE, which consists of the colorless, ring-open (o-DTE) and colored, ring-closed (c-DTE) isomers (Fig. 1).[48]
Summary
Materials that can be switched between different optical or fluorescent states have applications in data storage, biological imaging, logic operations, and sensing.[1,2,3,4,5,6,7,8,9,10] Such properties can be engineered with photochromic molecules, which undergo light-induced switching between isomers having distinct electronic states.Diarylethenes, fulgides, and spiropyrans are currently amongst the best performing photochromes and can be switched between ring-open and ring-closed isomers.[1,2,11,12,13] For diarylethenes and fulgides, the lowest energy, ring-open isomers are colorless, and the ring-closed isomers are colored. Following UV irradiation, both switches are in their colored forms, with the excitation light initiating ringclosed fulgide - ring-closed diarylethene FRET, quenching any fluorescence.
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