2025, Vol. 36 
b College of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
Stimulus-response systems have aroused increasing research interest due to their applications in controlled release [1], soft robot [2], controllable bioimaging [3], conducting switch [4], information encryption and anti-counterfeiting [5], etc. Several strategies such as covalent modification, doping and self-assembly have been employed to fabricate these intelligent systems. Thereinto, supramolecular self-assembly is a handy and feasible strategy for construct stimulation-responsive materials because it has the natural advantage of occurring spontaneously through non-covalent forces that are susceptible to external stimuli [6]. Molecular switches are the core component that forms the stimulus response systems, and it is relatively effortless to introduce responsive groups in supramolecular systems through self-assembling way [7]. Among various external stimuli, light is regarded as one of the most attractive candidates because of its noninvasiveness, easy controllability, low cost, and ubiquity [8]. Therefore, photoactive functional groups are utilized to build photosensitive intelligent materials. Compared with the other photoisomerized molecules, diarylethene (DAE) is considered as one of the most promising photochromic molecular switches owing to its absorption band separation, fast light-response, good thermal stability and preferable reversibility [9]. Hence, DAE derivatives are frequently involved in photoluminescent nanosystems to construct photomodulated supramolecular luminescent materials [10]. Furthermore, host-guest self-assembly gradually come into our view with the progress of host-guest recognition [11]. Host-guest competition is regarded as another important driving force for building stimulus-responsive smart systems [12]. However, it is relatively difficult to simultaneously introduce two or more stimulating factors in the same system for developing multiple stimuli materials. In recent years, room temperature phosphorescence (RTP) materials become gradually an indispensable member of the materials with function of photoluminescence due to their large Stokes shift and long-lived emission. Nevertheless, it is challenging to gain high-efficiency RTP because of low intersystem crossing (ISC) efficiency from singlet to triplet and fast nonradiative decay rate caused by the weak spin-orbit coupling (SOC) [13]. To date, some proven efforts have been made to increase emissive intensity and lengthen the emission lifetime of RTP materials, such as promoting SOC through the incorporation of heavy atoms, aromatic carbonyls or heteroatoms, and lessening the nonradiative transition rate [14–17]. Despite the rapid progress of RTP materials, and it is urgently desired but not easy to fabricate intelligently dynamic RTP materials with broader application prospects and meeting the practical requirements [18]. Noticeably, triplet-singlet Förster resonance energy transfer (TS-FRET) recently explored that energy transfer from the excited triplet state of RTP donors to singlet state of fluorescent acceptors, has been verified to be an alternative strategy to realize adjustable afterglow emission, which facilitates the great evolution of RTP materials [19–23]. Nevertheless, most adjustable long-lived luminescent materials all introduce one stimulus or multiple stimuli in parallel. It remains a formidable challenge to design and construct controllable purely organic long-lived luminescent materials with tunable color, lifetime and intensity encountering with logically ordered distinct stimuli by efficiently reversible control of TS-FRET process, which have been rarely reported yet, to the best of our knowledge.
In this work, cucurbituril and cyclodextrin-based supramolecular cascade assembling strategy was employed to drastically boost RTP performance of the water-soluble guest bromophenylpyridine-tethered-bromoisoquinoline (BPP-BQ) with heavy atoms by sequential macrocyclic confinement (Scheme 1). The obtained supramolecular assembly further self-organized to nanoaggregates that accommodated energy-matched fluorescent dyes emitted at long wavelengths to form light-harvesting system via TS-FRET pathway, presenting the long-lived emission of the energy acceptor with large Stokes shift. Besides, a water-soluble photoactive DAE derivative was introduced into the resultant light-harvesting system to prospectively endow it with the capacity of light response. Unstable host-guest interaction and photoisomerization peculiarity enabled the long-lived emissive supramolecular system with host-guest competition and light stimulation double modulation possibility, leading to promising realization of orderly dual stimulus-modulated long-lifetime photoluminescence.
|
Download:
|
| Scheme 1. Schematic illustration of the construction of logically ordered stimulus-controlled high-efficiency long-lived delayed luminescent switch though sequential assembling way based on TS-FRET light-harvesting platform. | |
The detailed synthetic routes, procedures and characterizations of BPP-BQ and reference compounds 3 and 4 were showed in Scheme S1 and Figs. S1–S9 (Supporting information). It is well known that CB[8] can include one or two right-sized guests with positive charge situated at end position into its rigid cavity [24–26]. In view of the structural feature of BPP-BQ, it should be possibly encapsulated in the hole of CB[8]. Firstly, the binding ratio of guest molecule BPP-BQ and host molecule cucurbit[8]uril (CB[8]) had been studied. As illustrated in Fig. S10 (Supporting information), a Job plot for the affinity of BPP-BQ with CB[8] displayed 1:1 host–guest stoichiometry, indicating a peak at molar fraction 0.5. Secondly, binding ability of BPP-BQ with CB[8] was subsequently conducted. As displayed in Fig. 1a, upon sequential addition of CB[8], the two absorption peaks of BPP-BQ at 245 nm and 304 nm both displayed an apparent decrease and bathochromic-shift, while one absorption band between 253 nm and 270 nm and the other one at 328–400 nm evidently increased, accompanied by the appearance of three isosbestic points at 253, 270 and 328 nm. These phenomena manifested the occurrence of complexing behaviors between BPP-BQ and CB[8] and the formation of binary supramolecular assembly BPP-BQ⊂CB[8]. By virtue of UV–vis absorption spectral titration above (Fig. 1a and Fig. S11 Supporting information), the complexing stability constant (KS) was determined to be 6.20 × 104 L/mol through analyzing the absorbance evolution at 308 nm with continuous addition of CB[8] to the aqueous solution of BPP-BQ by employing the nonlinear least-squares fitting method [27]. To disclose their assembling pattern, two unconnected methyl bromoisoquinoline (3) and bromophenylpyridine (4) salts as reference compounds instead of BPP-BQ were prepared and studied. We have performed 1H NMR spectra of 3 and 3 with CB[8] (Fig. S12 in Supporting information), revealing CB[8] only complexed with equivalent of 3. As shown in Fig. S13 (Supporting information), when 3, 4 and CB[8] was mixed together, 42⊂CB[8] and 3•4⊂CB[8] both existed, which was verified by their mass spectra (Fig. S14 in Supporting information). As manifested in Fig. S15a (Supporting information), UV–vis absorption spectra of 3⊂CB[8] and 42⊂CB[8] were considerably different from that of the only 3 and 4, and UV–vis absorption spectrum of 3/42⊂CB[8]2 was obviously different from that of 3⊂CB[8], 42⊂CB[8] or combined result of both, implying that some 3 and 4 were hybridizingly encased in the cavity of CB[8]. The similar phenomena could be observed in their photoluminescence spectral contrast (Fig. S15b in Supporting information). Subsequently, we conducted 1H NMR spectral titration of BPP-BQ with sequential addition of CB[8] (Fig. S16 in Supporting information), which displayed their 1H NMR signals did not change until 1 equiv. of CB[8] was added and further implied that binding stoichiometric ratio of the guest and CB[8] was 1:1. From 1H NMR spectral comparison of BPP-BQ and BPP-BQ⊂CB[8], half aromatic ring signal peaks displayed an apparent upfield shift, while the other half showed downfield shift or unchanged (Fig. S17 in Supporting information). Hence, BPP-BQ should be self-assembled with CB[8] to form most likely a 2:2 quaternary supramolecular complex, as illuminated in Scheme 1. The structural characteristic of BPP-BQ that was decorated by heavy atomic bromine presented prospectively RTP in a restricted environment confirmed by the reported literatures [15]. Inspired by this, the influence of CB[8] on photoluminescence especially RTP of the guest was subsequently studied. As displayed in Fig. S18 (Supporting information), when 1 equiv. of CB[8] was continuously added in the solution containing BPP-BQ, its photoluminescence intensity at 380 nm decreased gradually, while a new maximum emission peak at 530 nm that should be assigned to RTP emerged and rose little by little. In order to affirm that the emission was indeed phosphorescence, the phosphorescent spectral evolution of BPP-BQ was then inspected in the process of adding CB[8]. Notably, time-gated emission maximum at 530 nm of the guest was greatly enhanced in room temperature after adding macrocyclic host CB[8] (Fig. 1b) due to conformational confinement of CB[8] on guest molecules and promoting ISC, which was consistent with the aforementioned phenomena (Fig. S18). Besides, according to the time-resolved photoluminescence decay curve (Fig. S19 in Supporting information), the luminescent lifetime of the BPP-BQ⊂CB[8] assembly at 530 nm was measured to be 0.577 ms, which evidently affirmed that the emission at 530 nm belonged to RTP. Moreover, confinement-induced phosphorescence enhancement effect of the guest by both CB[6] and CB[7] inferior to that of CB[8] (Fig. S20 in Supporting information).
|
Download:
|
| Fig. 1. (a) UV–vis absorption spectral evolution of BPP-BQ (1 × 10–5 mol/L) with sequential addition of 0–2 equiv. of CB[8]. (b) Phosphorescence emission spectral evolution (delay = 50 µs) of BPP-BQ (5 × 10–5 mol/L) with sequential addition of 0–1 equiv. of CB[8]. (c) Phosphorescence emission spectral evolution (delay = 50 µs) of BPP-BQ⊂CB[8] with sequential addition of 0–0.33 equiv. of SCD (Inset: the change of luminescent photographs in this process). (d) The time-resolved photoluminescence decay curve of BPP-BQ⊂CB[8]-SCD ([BPP-BQ] =[CB[8]] = 5 × 10–5 mol/L) at 530 nm; λex = 306 nm. | |
However, RTP intensity of the binary assembly was still relatively weak, and needed urgently further improvement. For further boosting the RTP performance of the binary assembly, electronegative sulfonated β-cyclodextrin (SCD) was chosen to reform the supramolecular system above. To our delight, when SCD was gradually added into the solution containing BPP-BQ⊂CB[8], phosphorescence of the system at 530 nm manifested a substantial increase about 109 times that of the initial (Fig. 1c), and the RTP emission intensity was no longer enhanced with the introduction of 0.25 equiv. of SCD. Besides, it could be seen that the best mixing ratio of SCD and BPP-BQ⊂CB[8] was 1:4 given by the optical transmittance results (Fig. S21 in Supporting information), which was in accordance with their RTP titration. Visually, the green phosphorescence photograph of BPP-BQ⊂CB[8] was brightened with addition of 0.25 equiv. of SCD under 254 nm UV light (Fig. 1c, inset). Subsequently, the lifetime of ternary assembly BPP-BQ⊂CB[8]-SCD was measured and determined to be 1.265 ms (Fig. 1d), which was dramatically longer than that of BPP-BQ⊂CB[8] (0.577 ms). The photoluminescence quantum (PLQY) of BPP-BQ⊂CB[8] was enhanced from 2.2% to 3.5% with addition of SCD (Figs. S22a and b in Supporting information). In a word, SCD-induced aggregation brought the two favorable evolutions such as intensity enhancement and lifetime dilation of RTP, which was both attributed to the formation of a tighter aggregate assembled from the binary assembly and SCD by means of electrostatic interaction. Here, the presence of SCD could effectively inhibit non-radiative transitions and promote the triplet state, and the phosphorescent group was coated with SCD to further shield the oxygen quencher in the aqueous solution, eventually resulting in enhancement of ISC efficiency [28].
Next, transmission electron microscopy (TEM), scanning electron microscope (SEM), tyndall effect and dynamic light scattering (DLS) experiments were performed to represent further structural information of BPP-BQ⊂CB[8]-SCD. Tyndall effect experiment of the aqueous solution containing BPP-BQ⊂CB[8]-SCD showed an apparent light path (Fig. S23 in Supporting information), implying that the supramolecular assembly further formed nanoaggregates. Intuitively, the TEM images that many spherical nanostructures with diameter of about 71 nm appeared in our sight revealed that the BPP-BQ⊂CB[8]-SCD assembly further self-aggregated to form sphere-like nanoparticles (Fig. S24a in Supporting information). The above TEM result presented were subsequently proved by the SEM image (Fig. S24b in Supporting information). SCD could assemble with BPP-BQ⊂CB[8] via electrostatic interaction to form nanoparticles with alternate layer arrangement (Scheme 1) [25]. Besides, its average hydrodynamic diameter obtained from dynamic light scattering (DLS) data manifested 162.1 nm (Fig. S24c in Supporting information), which was greater than its spherical nanostructural diameter (71 nm) determined from TEM. These results implied that the nanoparticles should possess cavities like vesicles [29,30]. The above evidences altogether verified the two assemblies self-aggregated into relatively large nanoparticles.
Possessing large-scale nanostructures and high-performance RTP, the ternary assembly BPP-BQ⊂CB[8]-SCD could accommodate adaptive attachment sites for energy-matched fluorochromes with long-wavelength emission. Through survey of fluorescent dye Rhodamine B (RhB), it was selected as an energy acceptor to be loaded in consideration of perfect overlap between its absorption band and the RTP emission range of BPP-BQ⊂CB[8]-SCD (Fig. S25 in Supporting information). Then, time-gated emission spectral variation of BPP-BQ⊂CB[8]-SCD was investigated with the introduction of RhB. As discerned in Fig. 2a, upon continuous addition of a small quantity of RhB into the BPP-BQ⊂CB[8]-SCD aqueous solution, the phosphorescence intensity at 530 nm decreased gradually, while a new time-gated emission peak at 578 nm appeared and was progressively enhanced, which was assigned to the emission of RhB (Fig. S26 in Supporting information), accompanied by the change of photoluminescent color from green to yellow (Fig. 2b). Variation of the above emission color was consistent with coordinate change in the CIE diagram given by time-gated emission spectra (Fig. 2c). To our delight, a light-harvesting system based on energy transfer TS-FRET expressing typical long-lifetime delayed emission peculiarity came into being without doubt, and the energy-transfer mechanism was uncovered that the triplet energy of the donor was effectively transferred to the singlet state of the acceptor to achieve TS-FRET (Fig. 2d). This was because individual RhB did not possess RTP or long-lifetime delayed luminescence properties (Fig. S26). Notably, the emission intensity of the acceptor at 578 nm reached the maximum as the donor-acceptor ratio was 100:1 (Fig. 2a). In this case, the energy transfer efficiency (ФET) was calculated approximately to be 53%, and the antenna effect was determined to be up to 93 (see calculation details in Supporting information). Besides, the lifetimes of BPP-BQ⊂CB[8]-SCD@RhB at 530 nm and 578 nm were measured to be 1.045 ms and 1.066 ms, respectively (Fig. S27 in Supporting information). The presented photoluminescent lifetimes provided compelling evidence for the occurrence of TS-FRET in this light-harvesting system. The PLQY was increased from 3.5% to 5.4% in the formation of the light-harvesting process (Figs. S22b and c). Just as we expected, an artificial light-harvesting long-lifetime delayed photoluminescent system with tunable luminous color and intensity, and large Stokes shift about 272 nm based on TS-FRET had been handily constructed here.
|
Download:
|
| Fig. 2. (a) Phosphorescence emission spectral evolution (delay = 50 µs) of BPP-BQ⊂CB[8]-SCD ([BPP-BQ] = [CB[8]] = 5 × 10–5 mol/L, [SCD] = 1.25 × 10–5 mol/L, λex = 306 nm) with sequential addition of RhB. (b) Photographs of BPP-BQ⊂CB[8]-SCD with different RhB ratios under 254 nm UV light (RhB: 0–0.01 equiv.). (c) 1931 CIE chromaticity diagram of BPP-BQ⊂CB[8]-SCD with different RhB ratios in aqueous solution. (d) Proposed diagram of the TS-FRET process in BPP-BQ⊂CB[8]-SCD@RhB light-harvesting system. | |
Nevertheless, overwhelming majority of artificial light-harvesting systems reported have a lack of modulation capacity so far. As is well-known, light-harvesting systems of plants will be protected from damage through changing their energy-transfer pathways once exposed to strong light [31]. This gives us an inspiration to develop controllable artificial light-harvesting systems. Interestingly, long-lived photoluminescence of the BPP-BQ⊂CB[8]-SCD@RhB light-harvesting system displayed a dramatical reduction with relatively high quenching efficiency of 87% when intervened by 0.05 equiv. of a water-soluble competitive guest DAE (Scheme 1) [32] with two positive charges (Fig. 3a and Fig. S28a in Supporting information), which was possibly because binding interaction between BPP-BQ⊂CB[8] and SCD was disturbed by the DAE and then RTP performance deteriorated. Subsequent addition of superfluous 1.6 equiv. of SCD compelled the almost complete restoration of the initial RTP intensity due to the reformation of the ternary assembly BPP-BQ⊂CB[8]-SCD (Fig. 3a and Fig. S28b in Supporting information). Intuitively, the change of long-lived photoluminescence images in above process was presented under 254 nm UV light in Fig. 3a (inset). Hence, long-lifetime emission of the light-harvesting system was reversibly modulated through host-guest competition. For verifying this inference, some control experiments were afterwards conducted. For only BPP-BQ⊂CB[8]-SCD in the absence of energy acceptor RhB, similar experimental phenomena as that of the light-harvesting system were observed (Fig. S29 in Supporting information), which undoubtedly confirmed our deduction. It was particularly exciting that the light-harvesting system with long-lifetime emission could be switched by distinct light stimulation when incorporated by a spot of the DAE. Interestingly, BPP-BQ⊂CB[8]-SCD@RhB and BPP-BQ⊂CB[8]-SCD@RhB@DAE both formed nanoparticles, and grain diameter and average hydrodynamic diameter slightly turned small due to the introduction of DAE (Fig. S30 in Supporting information). As discerned in Fig. 3b and Fig. S31a in Supporting information), its RTP was greatly quenched by 83% upon irradiation at 254 nm ultraviolet (UV) light for 4 s, whose reason was probably that the introduced DAE was transformed into its energy-matched closed-form isomer, i.e., DAE(c) that intercepted this part of the energy transferred in the above TS-FRET of light-harvesting process. Subsequent irradiation of the resultant sample at >550 nm visible light for 18 s led to the recovery of the original emission intensity because the resultant DAE(c) returned to its original energy-mismatched open-form isomer DAE(o) and TS-FRET pathway was restored (Fig. 3b and Fig. S31b in Supporting information). The abovementioned visual photoluminescent photograph alterations were shown in Fig. 3b (inset). The proposed reasons above was proved by their spectral overlap that the RTP emission spectrum of BPP-BQ⊂CB[8]-SCD possessed perfect overlap with the absorption spectra of DAE(c) but no overlap with that of DAE(o) at all (Figs. S32 and S33 in Supporting information). And then, the assertive proofs were provided by some requisite control experiments. When the light-harvesting system based on TS-FRET lacked the RhB energy acceptor, the delayed photoluminescence of BPP-BQ⊂CB[8]-SCD loaded with a small quantity of the DAE regulator could be reversibly switched on/off by alternating 254 nm and >550 nm light (Fig. S34 in Supporting information), which were consistent with the photoswitching behaviors appearing in photomodulated light-harvesting system. In control experiments, BPP-BQ⊂CB[8]-SCD and BPP-BQ⊂CB[8]-SCD@RhB without DAE did not manifest light responsiveness (Fig. S35 in Supporting information), and the DAE did not express apparent fluorescence and phosphorescence (Fig. S36 in Supporting information). Therefore, our assertion on the photocontrolling mechanism was certainly verified by virtue of the above inspections, as shown in Scheme 1. In a word, TS-FRET pathway in the light-harvesting system could be disconnected and restored by photoisomerization of the DAE under distinct light illumination. Inspired by the two stimuli-regulation above, a wonderful thought came to our mind that a RTP switch with two stimuli in sequence could be designed and attempted. With this in our mind, the light-harvesting system was first intervened by the competitor and then illuminated at 254 nm, and the result revealed that the long-lived photoluminescence of the system was quenched by up to 98% that is a very high quenching efficiency (Figs. 3c and e), accompanied by visual luminescent photograph conversion from bright yellow to invisible to the naked eye (Fig. 3c, inset). Crucially, the initial delayed emission intensity could be completely recovered through first >550 nm visible light irradiation and then addition of a certain amount of SCD (Figs. 3d and f) along with the restoration of the original bright yellow luminescent photograph (Fig. 3d, inset). The delayed photoluminescent spectral evolution of BPP-BQ⊂CB[8]-SCD@DAE undergoing logically ordered host-guest competition and light-irradiation stimuli (Fig. S37 in Supporting information) exhibited the same change law as BPP-BQ⊂CB[8]-SCD@RhB@DAE, which further proved our hypothesized mechanism (Scheme 1). Therefore, we herein constructed two logically consecutive steps of stimulation-induced TS-FRET light-harvesting system with high-efficiency long-lifetime photoluminescent switching property.
|
Download:
|
| Fig. 3. (a) Time-gated emission spectral evolution (delay = 50 µs) of BPP-BQ⊂CB[8]-SCD@RhB with addition of alternating 0.05 equiv. of DAE and 1.6 equiv. of SCD (Inset: the change of luminescent photographs in this process). (b) Time-gated emission spectral evolution (delay = 50 µs) of BPP-BQ⊂CB[8]-SCD@RhB with addition of 0.05 equiv. of DAE upon irradiation at 254 nm and >550 nm light (Inset: the change of luminescent photographs in this process). (c) Time-gated emission spectral evolution (delay = 50 µs) of BPP-BQ⊂CB[8]-SCD@RhB with the addition of DAE (0–0.05 equiv.) and then upon irradiation at 254 nm light (Inset: the change of luminescent photographs in this process). (d) Time-gated emission spectral evolution (delay = 50 µs) of the resultant sample c upon irradiation at >550 nm light and then with addition of SCD (0–1.6 equiv.) (Inset: the change of luminescent photographs in this process). (e) The evolution of time-gated emission intensity at 580 nm of (c). (f) The evolution of time-gated emission intensity at 580 nm of the above Fig. d. [BPP-BQ] = [CB[8]] = 5 × 10–5 mol/L, [SCD] = 1.25 × 10–5 mol/L, [RhB] = 5 × 10–7 mol/L, λex = 306 nm. | |
In view of good host-guest competition and photoresponse performance of the above assemblies, they could be applied to information encryption and conversion. BPP-BQ⊂CB8-SCD and BPP-BQ⊂CB8-SCD@RhB solutions were used to spell out the luminous number pattern “8” under 254 nm UV light. However, local position of the pattern was disturbed by the DAE and phosphorescence of these segments was quenched, leading to the change of luminescent number pattern from “8” to “3” in our view (Fig. 4a). Afterwards, just the right amount of SCD was added to the luminescence-quenching parts resulted in the reemergence of the initial “8” again. Furthermore, another luminescent pattern formed by BPP-BQ⊂CB8-SCD@DAE and BPP-BQ⊂CB8-SCD@RhB@DAE aqueous solutions turned dark upon 254 nm light irradiation, and subsequently reappeared after >550 nm light illumination (Fig. 4b), benefiting from their delayed luminescent photoswitching properties. More significantly, the yellow luminescence-emitting digit “8” gradually became “6” via two-step ordered stimulation of adding DAE and 254 nm light irradiation, and could reappear again undergoing >550 nm light illumination and the addition of SCD in order (Fig. 4c). This logically ordered stimulation-controlled long-lived luminescent switching had better effect than that induced by the only host-guest competition or photostimulation in information encryption and conversion. These intelligent supramolecular systems expressed great application value in high-security-level information encryption and conversion.
|
Download:
|
| Fig. 4. (a) Photograph evolution of number pattern “8” obtained by BPP-BQ⊂CB8-SCD and BPP-BQ⊂CB8-SCD@RhB aqueous solutions with part addition of DAE and SCD. (b) Photograph evolution of the orange pattern obtained by BPP-BQ⊂CB8-SCD@DAE and BPP-BQ⊂CB8-SCD@RhB@DAE aqueous solutions upon irradiation at alternating 254 nm and >550 nm light. (c) Photograph evolution of number “8” obtained by BPP-BQ⊂CB8-SCD@RhB aqueous solution with local addition of DAE and upon irradiation at 254 nm light and subsequently addition of SCD and upon >550 nm irradiation in turn. (d) Photographs of BPP-BQ⊂CB8-SCD@RhB (PAM) films before and after the 254 nm UV lamp was turned off. (e) Photographs of BPP-BQ⊂CB8-SCD@RhB (PAM) freeze-drying solids before and after the 254 nm UV lamp was turned off. (f) Photographs of the letters “H A U” of the PAM films (“H”, “A” and “U” were prepared by BPP-BQ⊂CB8-SCD (PAM), BPP-BQ⊂CB8-SCD@RhB (PAM) and RhB (PAM)), respectively. The flower of PAM freeze-drying solids (The petals were made by BPP-BQ⊂CB8-SCD@RhB (PAM), the stem and the leave were made by BPP-BQ⊂CB8-SCD (PAM)) before and after the 254 nm UV lamp was turned off. | |
It was of significance to explore solid-state RTP properties of BPP-BQ⊂CB8-SCD and BPP-BQ⊂CB8-SCD@RhB. Polymers were chosen as attached matrixes for them because polymer-doping strategy was one of the most effective methods for acquiring new solid-state luminescent films with afterglow [17]. For acquiring new solid-state luminescent materials with afterglow, the two supramolecular assemblies were evenly doped in polyvinyl alcohol (PVA) and polyacrylamide (PAM) aqueous solution to form hydrogels and make films or network solid. The time-gated photoluminescent spectra in same test conditions showed that the phosphorescent intensity of the binary assembly BPP-BQ⊂CB[8] and the ternary assembly BPP-BQ⊂CB[8]-SCD were significantly enhanced after doping PVA or PAM to obtain the BPP-BQ⊂CB[8] (PVA/PAM) and BPP-BQ⊂CB[8]-SCD (PVA/PAM) films (Figs. S38 and S39 in Supporting information) in comparison with that of their solution state (Figs. 1b and c). Visually, the afterglow phenomena of the two binary and ternary supramolecular assemblies were almost invisible in the aqueous solution state, while green afterglow of their PVA and PAM films could be seen after the removal of 254 nm light source (Figs. S40a, S40c, S41a and S41c in Supporting information). It was worth noting that the TS-FRET process could still take place after doping PVA or PAM (Fig. S42 in Supporting information). As shown in Fig. 4d and Fig. S43a (Supporting information), the yellow afterglow of BPP-BQ⊂CB[8]-SCD@RhB (PVA/PAM) films could be seen after turning off the 254 nm light source. Furthermore, freeze-drying solids of the resultant hydrogels prepared by doping of these assemblies in PVA or PAM also all expressed afterglow photoluminescence behaviors (Fig. 4e and Figs. S40b, S40d, S41b, S41d and S43b in Supporting information). Interestingly, these afterglow hydrogel films were processable and can be made into a variety of patterns. As manifested in Fig. 4f, the three letters “HAU” were prepared by BPP-BQ⊂CB8-SCD (PAM), BPP-BQ⊂CB8-SCD@RhB (PAM) and RhB (PAM) hydrogel films, respectively. After turning off the UV lamp, the letters “H” and “A” displayed afterglow but “U” could not because RhB alone did not possess long-lifetime RTP. Furthermore, a flower fabricated using the BPP-BQ⊂CB8-SCD (PAM) and BPP-BQ⊂CB8-SCD@RhB (PAM) hydrogel freeze-drying solids exhibited an afterglow appearance after the removal of UV lamp (Fig. 4f). BPP-BQ⊂CB[8]-SCD@RhB (PAM) film doped by DAE expressed ligh responsiveness and applications in photorecording and anti-counterfeiting (Fig. S44 in Supporting information).
In summary, a water-soluble guest BPP-BQ had been designed and synthesized, and assembled with CB[8] to obtain a binary assembly BPP-BQ⊂CB[8], displaying an apparent green RTP on account of macrocyclic restriction. Subsequently, when SCD was introduced into the supramolecular system and form ternary assembly BPP-BQ⊂CB[8]-SCD, green RTP intensity of the system was dramatically boosted and the RTP lifetime was also apparently prolonged due to further assembly-induced aggregation. The ternary assembly further self-aggregated to form spherical nanoparticles, and could accommodate RhB to form a light-harvesting nanosystem BPP-BQ⊂CB[8]-SCD@RhB with long-lived emission and large Stokes shift based on TS-FRET from BPP-BQ⊂CB[8]-SCD to RhB, Interestingly, the long-lived luminescence of BPP-BQ⊂CB[8]-SCD@RhB can be efficiently switched with the efficiency of up to 98% by the aforementioned logically ordered host-guest interaction and light irradiation stimuli. This special long-lived emission switching peculiarity enabled the tunable light-harvesting system to be used for high-security-level information encryption and transformation. In addition, the integration of the BPP-BQ⊂CB[8]-SCD and BPP-BQ⊂CB[8]-SCD@RhB assemblies with polyvinyl alcohol or polyacrylamide prepared two high-efficiency photoluminescent films with long afterglow. The presented construction method and new stimulus-responsive strategies facilitated the development of dynamic pure organic long-lived photoluminescent materials.
Declaration of competing interestThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statementXinhui Fan: Writing – original draft, Methodology, Investigation. Yonghao Fan: Investigation. Yuli Dang: Methodology. Puhui Xie: Methodology. Xin Li: Investigation. Zhanqi Cao: Methodology. Song Jiang: Methodology. Lijie Liu: Investigation. Xin Zheng: Investigation. Lixia Xie: Investigation. Caoyuan Niu: Methodology. Guoxing Liu: Writing – review & editing, Writing – original draft, Supervision, Funding acquisition. Yong Chen: Writing – review & editing.
AcknowledgmentsWe thank the National Natural Science Foundation of China (Nos. 21801063, 22305070 and U20041101) and the Top-Notch Talents Program of Henan Agricultural University (Nos. 30501049 and 30501032) for financial support.
Supplementary materialsSupplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110648.
| [1] |
X. Ma, Y. Zhao, Chem. Rev. 115 (2015) 7794-7839. DOI:10.1021/cr500392w |
| [2] |
M. Dong, W. Liu, C.F. Dai, et al., Mater. Horiz. 11 (2024) 2143-2152. DOI:10.1039/d3mh02247a |
| [3] |
G. Liu, X. Xu, X. Dai, et al., Mater. Horiz. 8 (2021) 2494-2502. DOI:10.1039/d1mh00811k |
| [4] |
C. Jia, A. Migliore, N. Xin, et al., Science 352 (2016) 1443-1445. DOI:10.1126/science.aaf6298 |
| [5] |
G. Liu, C. Tian, G. Li, et al., ACS Mater. Lett. 5 (2023) 2299-2307. DOI:10.1021/acsmaterialslett.3c00613 |
| [6] |
L. Yang, Y. Li, H. Zhang, et al., Chin. Chem. Lett. 34 (2023) 108108. |
| [7] |
G. Liu, Y. Li, C. Tian, et al., Chin. Chem. Lett. 35 (2024) 109403. |
| [8] |
M. Chen, M. Zhong, J.A. Johnson, Chem. Rev. 116 (2016) 10167-10211. DOI:10.1021/acs.chemrev.5b00671 |
| [9] |
G. Liu, C. Tian, X. Fan, et al., JACS Au 3 (2023) 2550-2556. DOI:10.1021/jacsau.3c00342 |
| [10] |
H.B. Cheng, S. Zhang, E. Bai, et al., Adv. Mater. 34 (2022) 2108289. |
| [11] |
D.H. Qu, Q.C. Wang, Q.W. Zhang, X. Ma, H. Tian, Chem. Rev. 115 (2015) 7543-7588. DOI:10.1021/cr5006342 |
| [12] |
T. Cui, G. Liu, W. Zhang, et al., Chin. Chem. Lett. 32 (2021) 357-361. |
| [13] |
B. Ding, X. Ma, H. Tian, Acc. Mater. Res. 4 (2023) 827-838. DOI:10.1021/accountsmr.3c00090 |
| [14] |
J. Song, Y. Zhou, Z. Pan, et al., Matter 6 (2023) 2005-2018. |
| [15] |
Z.Y. Zhang, Y. Chen, Y. Liu, Angew. Chem. Int. Ed. 58 (2019) 6028-6032. DOI:10.1002/anie.201901882 |
| [16] |
H. Xiang, J. Cheng, X. Ma, X. Zhou, J.J. Chruma, Chem. Soc. Rev. 42 (2013) 6128-6185. DOI:10.1039/c3cs60029g |
| [17] |
L. Zhou, J. Song, Z. He, et al., Angew. Chem. Int. Ed. 63 (2024) e202403773. |
| [18] |
Q. Zhou, C. Yang, Y. Zhao, Chem 9 (2023) 2446-2480. |
| [19] |
X.Y. Dai, M. Huo, Y. Liu, Nat. Rev. Chem. 7 (2023) 854-874. DOI:10.1038/s41570-023-00555-1 |
| [20] |
S. Kuila, S.J. George, Angew. Chem. Int. Ed. 59 (2020) 9393-9397. DOI:10.1002/anie.202002555 |
| [21] |
Q. Dang, Y. Jiang, J. Wang, et al., Adv. Mater. 32 (2020) 2006752. |
| [22] |
H. Gui, Z. Huang, Z. Yuan, X. Ma, CCS Chem. 4 (2022) 173-181. DOI:10.31635/ccschem.021.202000609 |
| [23] |
X. Zhou, X. Bai, F. Shang, et al., Nat. Commun. 15 (2024) 4787. |
| [24] |
H. Nie, Z. Wei, X.L. Ni, Y. Liu, Chem. Rev. 122 (2022) 9032-9077. DOI:10.1021/acs.chemrev.1c01050 |
| [25] |
J. Li, Y. Zhang, S. Liu, et al., Chin. Chem. Lett. 35 (2024) 109645. |
| [26] |
L. Mao, S. Li, X. Zhang, Z.T. Li, D. Ma, Chin. Chem. Lett. 35 (2024) 109363. |
| [27] |
Y.X. Wang, Y.M. Zhang, Y. Liu, J. Am. Chem. Soc. 137 (2015) 4543-4549. DOI:10.1021/jacs.5b01566 |
| [28] |
F.F. Shen, Z. Liu, H.J. Yu, et al., Adv. Opt. Mater. 10 (2022) 2200245. |
| [29] |
H.J. Wang, H.Y. Zhang, W.W. Xing, et al., Chin. Chem. Lett. 33 (2022) 4033-4036. |
| [30] |
K. Wang, D.S. Guo, X. Wang, Y. Liu, ACS Nano 5 (2011) 2880-2894. DOI:10.1021/nn1034873 |
| [31] |
J. Standfuss, A.C.T. van Scheltinga, M. Lamborghini, W. Kühlbrandt, EMBO J. 24 (2005) 919-928. DOI:10.1038/sj.emboj.7600585 |
| [32] |
G. Liu, Y.M. Zhang, C. Wang, Y. Liu, Chem. Eur. J. 23 (2017) 14425-14429. DOI:10.1002/chem.201703562 |