Room-Temperature High-Efficiency Solid-State ... - ACS Publications

Research Article www.acsami.org

Room-Temperature High-Efficiency Solid-State Triplet−Triplet Annihilation Up-Conversion in Amorphous Poly(olefin sulfone)s Andrey Turshatov,*,† Dmitry Busko,† Natalia Kiseleva,† Stephan. L. Grage,‡ Ian A. Howard,†,§ and Bryce S. Richards*,†,§ †

Karlsruhe Institute of Technology, Institute of Microstructure Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany ‡ Karlsruhe Institute of Technology, Institute of Biological Interfaces IBG-2, P.O. Box 3640, 76021 Karlsruhe, Germany § Karlsruhe Institute of Technology, Light Technology Institute, Engesserstrasse 13, 76131 Karlsruhe, Germany S Supporting Information *

ABSTRACT: Triplet−triplet annihilation up-conversion (TTA-UC) is a developing technology that can enable spectral conversion under sunlight. Previously, it was found that efficient TTA-UC can be realized in polymer hosts for temperatures above the polymer’s glass transition (T > Tg). In contrast, TTA-UC with high quantum yield for temperatures below Tg is rarely reported. In this article, we report new polymer hosts in which efficient TTA-UC is observed well below Tg, when the polymer is in a fully solid state. The four poly(olefin sulfone) hosts were loaded with upconversion dyes, and absolute quantum yields of TTA-UC (ηTTA‑UC) were measured. The highest value of ηTTA‑UC = 2.1% was measured for poly(1-dodecene sulfone). Importantly, this value was the same in vacuum and at ambient conditions, indicating that the host material acts as a good oxygen barrier. We performed time-resolved luminescence experiments in order to elucidate the impact of elementary steps of TTA-UC. In addition to optical characterization, we used magic angle spinning solid-state NMR experiments to estimate the T2 transverse relaxation time. Relatively long T2 times measured for poly(olefin sulfone)s indicate an enhanced nanoscale fluidity in the studied (co)polymers, which unexpectedly coexists with a rigidity on the macroscale. This would explain the exceptional triplet energy transfer between the guest molecules, despite the macroscopic rigidity. KEYWORDS: sensitized light up-conversion, triplet−triplet annihilation, triplet−triplet energy transfer, poly(olefin sulfone), porphyrin, T2 transverse relaxation time

■

INTRODUCTION Triplet−triplet annihilation up-conversion (TTA-UC) can convert low energy photons to photons with higher energy under moderate excitation conditions (comparable with excitation by solar illumination).1,2 TTA-UC occurs in a sequence of several basic steps: (i) absorption of photon by a sensitizer molecule; (ii) intersystem crossing in the sensitizer from singlet to triplet exciton; (iii) triplet−triplet energy transfer (TTET) from the sensitizer to an emitter molecule; (iv) TTA between two emitter molecules; and finally, (v) emission (from excited singlet level of emitter) of a photon with energy higher than energy of the absorbed photon (Figure S1). In the past, it has been demonstrated that TTA-UC has potential applications in photovoltaics,2,3 the generation of solar fuels,4,5 bioimaging,6,7 nanoparticle phototargeting,8 and oxygen sensing.9 For several of these applications, the components used for TTA-UC should be ideally encapsulated into rigid polymer hosts. The encapsulation can provide higher mechanical stability, better oxygen barrier properties, and © 2017 American Chemical Society

easier processing via extrusion or molding. Although achieving up-conversion in a rigid polymer host has been attempted several times,10−12 quantum yield of TTA-UC (ηTTA‑UC) has been rarely reported. Merkel et al.13 has shown that a sensitizer and an emitter can be embedded in a polymer matrix with a high glass transition temperature (Tg) such as poly(methyl methacrylate) (pMMA). However, the reported ηTTA‑UC in such a rigid matrix was less than 0.02%. Monguzzi et al. have described that TTA-UC can be detected in a cellulose acetate matrix below its Tg of 336 K; however, the ηTTA‑UC was reduced by 3 orders of magnitude when compared to the corresponding quantum yield in a tetrahydrofuran solution.1 Recently, Raisys et al. were able to demonstrate TTA-UC in pMMA films heavily doped with a sensitizer and an emitter (up to 40 wt % of an emitter) with ηTTA‑UC = 0.9%.14 All other successful demonstrations of TTA-UC in a solid phase relate to very Received: October 4, 2016 Accepted: February 2, 2017 Published: February 2, 2017 8280

DOI: 10.1021/acsami.6b12625 ACS Appl. Mater. Interfaces 2017, 9, 8280−8286

Research Article

ACS Applied Materials & Interfaces soft polymer matrixes with low Tg. Islangulov et al. have reported efficient TTA-UC in a medium consisting of a rubbery host with Tg of about 236 K.15 Singh-Rachford et al. have further demonstrated that cooling of the elastomer films to temperatures below the Tg completely suppresses the UC emission.16 Marsico et al. reported ηTTA‑UC = 1.2% for TTA-UC in hyperbranched unsaturated poly(phosphoester) under ambient conditions.17 Recently, Monguzzi et al. investigated TTA-UC in acrylic rubber polymers and reported an excellent ηTTA‑UC = 12% in poly(octyl)acrylate host with Tg = 211 K but an unmeasurable efficiency in poly(lauryl)acrylate with Tg = 270 K.18 Thus, the combination of a macroscopically mechanically stiff matrix and efficient upconversion remains a key research challenge. An alternate approach is to incorporate dyes for TTA-UC into ultrasmall polymer nanoparticles. The ηTTA‑UC = 2.5% and 7.5% was demonstrated recently for highly cross-linked polystyrene19 and semi crystalline poly(ε-caprolactone)20 nanoparticles, respectively. Here, we report homogeneous TTA-UC systems with rigid polymer hosts that exhibit TTA-UC at ambient temperature with a high ηTTA‑UC. Using poly(1-dodecene sulfone), (co)polymer with Tg in range of 315 K, we achieved 2.1% upconversion quantum yield in air at room temperature.

■

RESULTS AND DISCUSSION In our work, we synthesized family of poly(olefin sulfone) (POS) (co)polymers via radical chain growth polymerization of SO2 and the alkene at low temperature (Figure 1a). (Co)polymers of SO2 and 1-decene (POS10), 1-dodecene (POS12), 1-tetradecene (POS14) and 1-hexadecene (POS16) were obtained as a colorless tough polymer soluble in many organic solvents such as toluene, dichloromethane, tetrahydrofuran and acetone. (Co)polymers obtained in this way usually have a 1:1 ratio of perfectly alternating sulfone and olefin units when there is an alkyl moiety directly linked to the olefinic residue.21 The polymer product was validated using 13C and 1H magic angle spinning solid-state NMR (MAS-SS-NMR) (Figure 1b,c, respectively), where all carbon sites of the aliphatic tail could be identified in the 13C NMR spectrum in agreement with Callan et al.22 Proton and carbon T2 relaxation times were measured employing the MAS-SS-NMR experiment and will be discussed in more detail below. The Table S1 lists estimated material parameters of the POS (co)polymers. Note that values of Tg lie above room temperature (Tambient). Molecular weights correspond to values reported in the literature where the same synthetic route has been used.23 As a TTA-UC system, we chose the pair of platinum octaethylporphyrin (Pt-OEP) and perylene. This system, from our experience, demonstrates better photochemical stability than other well-characterized pairs such as Pt-OEP/diphenyl anthracene. In the following text, we will discuss the behavior of the POS12 host (the host with the highest ηTTA‑UC), whereas characteristics of other POS hosts are described in the Supporting Information. Importantly, the POS12 (co)polymer exhibits the ability to dissolve significant amount of the dyes without molecular aggregation. Figure 2a shows optical transmission and luminescent spectra of the POS12 host loaded with 2.5 wt % of perylene and 0.073 wt % of Pt-OEP (in molar ratio 100:1). In contrast to solvent cast pMMA loaded with perylene, where the aggregation starts at concentration of perylene

Figure 1. (a) Synthesis of POS (co)polymers; (b) 1H MAS-SS-NMR spectra of POS12 with signals of the methanediyl (−CH2−) and methyl (−CH3) groups at 1.2 and 0.8 ppm, respectively; (c) 13C MASSS-NMR spectra of POS12, obtained with single pulse excitation and 70 kHz 1H-decoupling at 25 kHz MAS. 1H and 13C signals of the main polymer chain give rise to very broad downfield signals, indicating probably a short T2.

0.25%,24 there is no evidence of the dye aggregation in POS (co)polymers at concentration 1 order of magnitude higher. The luminescence spectrum of perylene in POS films under 380 nm excitation demonstrates strong effect of self-absorption at λ < 480 nm. For comparison, the luminescence spectrum of perylene in a diluted cyclohexane solution is presented either. Overlaying the two luminescent spectra at λ > 510 nm, where self-absorption is minimal, clearly demonstrates a change of spectral shape, which is more pronounced at shorter emission wavelengths. It should be pointed out that the broad luminescence peak from perylene aggregates with a maximum at 530 nm, typically observed in case of pMMA host, does not appear in our samples.24 When the POS12 film doped with the UC dyes was excited at λ = 532 nm, up-conversion luminescence with a maximum at 476 nm and phosphorescence with a maximum at 648 nm were detected. The normalized luminescence spectra of POS12 host doped with Pt-OEP/perylene under ambient and vacuum conditions are plotted in Figure 2b. Importantly, even under ambient conditions, UC luminescence is easily measurable and can be characterized without special vacuum equipment or glovebox encapsulation. This allowed us to measure the absolute value of ηTTA‑UC using a standard integrating sphere. After characterization in the integrating sphere, the film was transferred into a vacuum chamber equipped with optical windows. Two measurements were performed: first, measure8281


Research Article

ACS Applied Materials & Interfaces

This sequence of measurements enables us to make a rough calculation of ηTTA‑UC under vacuum by simple comparison of the UC intensities I(476 nm;vacuum) and I(476 nm;ambient) measured in the vacuum chamber and assuming that the values of ηTTA‑UC measured under ambient conditions in the vacuum chamber and in the integrating sphere are similar (eq 1): ηTTA ‐ UC(vacuum) = ηTTA ‐ UC(ambient)

I(476nm;vacuum) I(476nm;ambient)

(1)

The highest value of ηTTA‑UC = 2.1% was obtained for vacuum conditions, whereas for ambient conditions, only slightly smaller value ηTTA‑UC = 2.o % was measured. The values of ηTTA‑UC for the other POS (co)polymers are presented in Table S2. The highest values of the ηTTA‑UC were achieved after purification of the POS12 (co)polymer by 6-fold repetition of a dissolution (in DCM)/precipitation (with methanol) cycle. Interestingly, after repeating the dissolution/precipitation cycle three times, size exclusion chromatogram still reflects an existence of two fractions with the peak molecular weight of o.3 kDa and 29.9 kDa. This intermediate polymer showed ηTTA‑UC(ambient) = 0.3% and ηTTA‑UC(vacuum) = 1.9%. Apparently, the fraction with low molecular weight has a large importance for the oxygen permeability through the polymer film and thus for quenching of triplet states, but it only has a limited effect on ηTTA‑UC under oxygen free conditions. In further experiments, we estimated efficiencies of the elementary steps of the UC, for example, TTET (ηTTET), TTA (ηTTA), and fluorescence of perylene (η), taking into account that efficiency of ISC (ηISC) in the case of Pt-OEP is close to unity. The value of η in the case of the POS12 film (thickness and film area were similar to the characteristics of the film for the UC experiment) that is doped only with 2.5 wt % of perylene under prompt excitation λ = 405 nm was estimated in the integrating sphere as 63%. The phosphorescence decays of Pt-OEP at 645 nm (Figure S7) were measured at different concentrations of perylene and reflect a decrease of the Pt-OEP lifetime from 99 μs down to 3 μs when ratio between perylene and Pt-OEP increase from 0 up to 100 (Figure 3a). The efficiency of the triplet energy transfer between the sensitizer and the emitter was calculated using eq 2 with a maximum value 96% at a 100/1 emitter-to-sensitizer ratio. τ ηTTET = 1 − τ0 (2)

Figure 2. (a) Optical transmission (black line) and luminescent spectra (blue line) of the POS12 film doped with 2.5 wt % of perylene and 0.073 wt % of Pt-OEP, λexc = 380 nm. Luminescent spectra of perylene in cyclohexane (1 × 10−6 M) (sky blue line), λexc = 380 nm; (b) Normalized TTA-UC luminescence spectra under ambient conditions in the integrating sphere (blue line) and in the vacuum chamber (red line). The POS12 film was doped with 2.5 wt % of perylene and 0.073 wt % of Pt-OEP. λexc = 532 nm, Pexc = 160 mW/ cm2; (c) Photograph of POS12 polymer. (d) Photograph of UC luminescence in the casted POS12 film doped with 2.5 wt % of perylene and 0.073 wt % of Pt-OEP, λexc = 532 nm. The photograph was taken under daylight with defocused laser beam (Pexc ∼ 50 mW/ cm2) and a combination of a notch filter (532 nm Semrock Inc.) and a short pass filter (600 nm, Thorlabs).

The proportion of triplets decaying by the second order TTA process (ηTTA) were calculated using the follow equation25 ηTTA = 1 −

β−1 ln(1 − β) β

(3)

where β is the initial fraction of decay that occurs through the second-order channel (TTA). For a given excitation power (Pexc), the value of β was estimated by fitting of experimental decays of UC luminescence (Figure S8) with the following equation

ments of luminescence under low pressure (10−8 bar) and, second, measurements under ambient conditions from the same excitation spot on the film. It should be noted that the UC spectra measured in the integrating sphere and in the vacuum chamber are slightly different because different optical schemes for the detection of the luminescence were used (Figure S2). In contrast to measurement in the vacuum chamber, the spectrum measured in the integrating sphere showed a noticeable self-absorption of the peak at 452 nm.

⎞2 ⎛ 1−β IUC(t ) ∝ IUC(0)⎜ ⎟ ⎝ exp(k1t ) − β ⎠

(4)

Figure 3b displays the dependence of ηTTA versus power density (Pexc), whereas values of the fitted parameters IUC(0), k1, and β are presented in Table S3. Naturally, the value of ηTTA is rising 8282


Research Article


However, in the present investigation, the calculation of f cannot be performed due to a complex behavior of the UC system. The complex behavior is emphasized in Figure 3b, where TTA-UC intensity as a function of excitation power density is presented. Straight lines in Figure 3b show the slope and indicate a deviation from behavior with n = 1 for the high irradiance regime and n = 2 for the low irradiance regime.26 Moreover, this dependence cannot be analyzed in a way similar to recently published studies,18,19 for example, using the concept of the excitation power threshold (Ith)a boundary between high and low irradiance regimes. Several additional effects can make vague the estimation of Ith. In further discussion, we will demonstrate the strong effect of temperature on IUC. Thus, local heating within the excitation spot might be responsible for deviation from the standard behavior at high excitation power density. Additionally, coexisting of polymer domains with different viscosity should be likely taken into account. Partial trapping of the dyes in domains with higher viscosity might also lead to the previously mentioned deviation in both the high and low irradiance regime. Figure 4a shows a temperature dependence of TTA-UC in the POS 12 host. Its complex trend exhibits a maximum at a temperature close to room temperature, whereas cooling to 273

Figure 3. (a) Phosphorescence lifetime (blue triangles) and efficiency of triplet−triplet energy transfer (black cycles) as a function of PtOEP/perylene ratio, concentration of Pt-OEP-0.073 wt %; (b) Fraction of triplets decaying by triplet−triplet annihilation (black cycles) and intensity of TTA-UC as a function of excitation power density (blue cycles). All measurements were performed in the vacuum chamber at 10−8 bar, λexc = 532 nm, concentration of Pt-OEP0.073 wt % and perylene-2 wt %.

with increasing Pexc. Half of the triplets decay via TTA at a power density of around 200 mW/cm2. At the highest excitation power density TTA dominates, but still a significant fraction of triplets are lost to monomolecular processes (ηTTA = 64% at Pexc = 300 mW/cm2). This nonlinear behavior of TTAUC in POS/Pt-OEP/perylene mixtures even at high Pexc illustrates that triplet−triplet annihilation between emitters in this solid matrix is still a limiting factor for the overall quantum yield of upconversion as well as the illumination intensities required to obtain the best quantum yield. The probability of obtaining an excited singlet state via the TTA process is smaller than ηTTA and is scaled down by a factor f due to the statistical probability of an annihilation via encounter complex with different multiplicity: singlet, triplet, or quintet (Figure S4). Considering different models for annihilation of triplet states, the value of f was estimated to be equal to 0.4 or even approaching to unity.1 The value for the spin-statistical factor f can be obviously estimated from eq 5 taking into account efficiencies determined for the elementary steps of TTA-UC. 1 IUCηTTA ‐ UC = ηISCfηTTA ηTTETη (5) 2

Figure 4. (a) Intensity of TTA-UC (at λ = 476 nm, blue cycles) and phosphorescence (at λ = 648 nm, black cycles) as a function of temperature. λexc = 532 nm. (b) ηTTET as a function of temperature (black cycles). Intensity of perylene fluorescence (λexc = 405 nm) as a function of temperature (blue cycles). All measurements were performed for the POS12 (co)polymer doped with 2.5 wt % of perylene and 0.073 wt % of Pt-OEP. 8283


Research Article


Results of calculations of the T2 values from 13C MAS-SSNMR spectra (Figure S10) demonstrate a similar trend. T2 measurements have been used earlier in studies of TTAUC by Monguzzi et al.18 In their analysis of the behavior of acrylic rubber polymers T2, experiments assisted in comparing the local mobility of the different polymer segments. It is interesting to compare our results from the present work to those obtained by Monguzzi et al. At room temperature, the POS12 (co)polymer demonstrates significantly longer T2 times than for poly(ethyl)acrylate (T2 = 0.19 ms)a polymer with a much lower Tg of 262 K. Furthermore, the local mobility of side chains in the POS (co)polymers is comparable or even higher than the local mobility of side chains in rubbery polymers with very low Tg (T2 = 2.52 ms, Tg = 211 K for poly(octyl)acrylate). In general, an unusual structural behavior of poly(olefin sulfone) has attracted attention already in the early 1990s. It has been shown that the main chain forms a stiff helix, whereas long flexible side chains stabilize the helix promoting fluidity, thus allowing POS16 to demonstrate main chain liquid crystallinity.22,28,29 We assume that at ambient temperature, POS (co)polymers behave like reinforced soft materials combining nanoscale fluidity and rigidity on the macroscale. The nanoscale fluidity can provide necessary dye mobility and, thus, efficient TTA-UC.

K or heating to 355 K both result in a loss of 90% of the intensity. This result correlates with the temperature behavior of the TTA-UC observed by Monguzzi et al.19 and Thévenaz et al.20 for ultrasmall polymer nanoparticles. In the meantime, Figure 4b indicates that an increase in temperature (T > 300 K) does not change significantly ηTTET and η. Thus, triplet−triplet annihilation is the process that slows dramatically when the temperature increases above 315 K, which might be due to decrease of the emitter triplet lifetime. It is commonly accepted that TTET and TTA occur via the Dexter electron exchange mechanism and, thus, require intimate contacts between the molecules. The values for ηTTET, ηTTA, and ηTTA‑UC obtained in our work are unusually high for polymers with Tg > Tambient. In solutions, molecules diffuse freely and easily interact, which results in high efficiency of TTA-UC. In contrast, in a solid matrix, the diffusion of dyes is constrained and dyes are often not mobile enough to realize efficient energy transfer. Thus, on one hand, a beneficial feature of POS systems lies in the high solubility of dyes in the polymer host that leads to an increase of the probability of intramolecular contacts. On the other hand this factor alone cannot explain the surprisingly high values of the ηTTET, ηTTA, and ηTTA‑UC. In order to explain this behavior, we measured the transverse relaxation time T2 in 1H MAS-SS-NMR experiments (results for the different POS (co)polymers are presented in Figure S9). The T2 relaxation time is sensitive to molecular motions which are slow compared to the Larmor frequency. Long T2 values (in the range of milliseconds) are characteristic for mobile molecules/segments present in fluids or soft solids such as elastomers, whereas short T2 values (in the range of microseconds) are characteristic for rigid molecules/segments as found in crystallites or glasses.27 Figure 5 displays T2 values for POS12 (co)polymer at different temperatures calculated from 1H MAS-SS-NMR

■

CONCLUSIONS In conclusion, the discovery of poly(olefin sulfone)s as a new class of a polymer hosts for TTA-UC makes significant headway in the challenge of realizing efficient solid-state TTAUC systems. In our opinion, starting from poly(olefin sulfone)s, significant progress in enhancement of ηTTA‑UC under ambient conditions can be achieved through a proper design of polymer materials.

■

EXPERIMENTAL SECTION

Synthesis. (Co)polymers (Figure 1a) were synthesized in agreement with the literature procedure.16 Briefly, SO2 (SigmaAldrich) was condensed into glass flask at −40 °C. Then 1-dodecene was added to the reaction flask. Afterward 5−6 M solution of tert-butyl peroxide in decane (Sigma-Aldrich) was injected into reaction mixture. After complete reaction, the (co)polymer (POS12) was purified by repeating dissolution (DCM)/precipitation (methanol) cycle. Other (co)polymers POS10, POS14, and POS16 were synthesized by a similar approach. All alkenes were purchased from Sigma-Aldrich and used without additional purification. Characterization of (Co)polymers. Glass transition temperature of (co)polymers was estimated with differential scanning calorimetry (TA-Instruments Q200). Molecular weight was estimated with size exclusion chromatography (Agilent 1200 series) in THF. Nuclear Magnetic Resonance. 13C and 1H MAS-SS-NMR experiments were performed using a Bruker Avance spectrometer (Bruker Biospin, Karlsruhe, Germany) operating at 600 and 152 MHz 1 H and 13C resonance frequency, respectively, equipped with a doubleresonance magic angle spinning probe for rotors of 2.5 mm outer diameter. The spectra were acquired at 25 kHz magic angle spinning following a single-pulse excitation. The T2-relaxation times were obtained using a Hahn echo sequence. All 1H NMR measurements were preceded by a presaturation sequence of several 90°-pulses. The 90°-pulse lengths were 2.5 and 3.125 μs for 1H and 13C, respectively. The signal was acquired for 160 ms and 40 ms with recycle delays of 4s and 8s in the case of 1H and 13C, respectively. Sixteen scans in the case of 1H NMR spectra and 512 scans in the case of 13C were accumulated. The error of the temperature was approximately ±1K. Optical Spectroscopy. For up-conversion experiments, a POS (co)polymer and dyes−perylene and platinum octaethylporphyrin (PtOEP) were dissolved in toluene (spectrophotometric grade, Sigma-

Figure 5. T2 relaxation time of the POS12 methanediyl (blue cycles) and methyl 1H NMR signal (red cycles) obtained with the Hahn echo experiment as a function of temperature, λexc = 532 nm. Concentration of Pt-OEP-0.073 wt % and perylene-2 wt %.

spectra with for the signals of the methanediyl and methyl groups of side chains at 1.2 and 0.8 ppm, respectively. Our results demonstrate that the methyl group, in general, is more mobile than the methanediyl groups. In addition, we observed T2 values to increase with increasing temperature. However, the T2 values level off when the temperature exceeds Tg. 8284


Research Article

ACS Applied Materials & Interfaces ORCID

Aldrich). Then certain amounts of the solutions were mixed and quantities were adjusted in order to provide typical dye concentrations 2.5 wt % of perylene and 0.073 wt % of Pt-OEP in a POS (co)polymer. Dye-doped POS thin films were prepared by drop-casting toluene solutions, in which the (co)polymer concentration was fixed at 10 wt %, onto glass plates. Obtained films were pre dried under ambient conditions and finally dried at 50 °C under vacuum. The thickness of the POS films was estimated to be 50−100 μm. Absolute value of luminescent quantum yield and luminescence decays were measured with a home-built optical system presented in Figure S5. As the excitation source, the 532 nm DPSS laser (DJ532− 40, Thorlabs) mounted in temperature stabilized mount (TCLDM9, Thorlabs) and driven by the laser diode controller (ITC4001, Thorlabs) was used. The power of the laser beam was adjusted by the use of the controlled rotatable neutral density filter (Thorlabs). The absolute values of quantum yield were measured and calculated according to the 3M procedure.30,31 For the quantum yield measurements the laser beam was directed into the integrating sphere (Labsphere) with a diameter of 15 cm. The high OH optical fiber with a diameter 1 mm (FP1000URT, Thorlabs) was used for collection of the emission from the integrating sphere and transferring light to the CCD spectrometer (C200, Thorlabs). For the improvement of detection of the TTA-UC and phosphorescence spectra, a 532 nm notch filter (NF03−532E−25, Semrock) was placed in front of the fiber. During the absorption measurement (measurement of the laser intensity at the direct excitation of the sample and indirect excitation of empty sphere), the notch filter was removed, and the integration time of the CCD spectrometer was changed to the lower value. All raw detected spectra were recalculated to the power spectra using an integration time value. The linearity of the signal versus integration time of CCD was proven experimentally. The spectral response of the whole detection system was calibrated using a calibration lamp (HL3plus-INT-CAL, Ocean Optics), and the correction was further applied to the power spectra. For the decay measurements, the multichannel scaling (TimeHarp 260, PicoQuant) was used. The spectral separation of the photoluminescence was done in the double monochromator (DTMS300, Bentham), and the emission at specific wavelength (472 nm for TTAUC and 644 nm for the phosphorescence) was detected by a counting PMT (R928P, Hamamatsu, mounted in cooled housing (CoolOne, Horiba). Modulation of the DPSS laser was achieved via the built-in function generator with a frequency of 10 Hz and a duty cycle 50%. All presented lifetimes were measured for the sample placed in the custom-made vacuum chamber vacuumed down to 10−5 hPa (10−8 bar). For the estimation of the difference in quantum yield values under vacuum and under ambient atmosphere, photoluminescence spectra from the same spot on the sample were measured by the same scanning double monochromator and PMT. Temperature dependence of up-conversion was measured using optical heating stage (MHCS622-V/G, Microptik BV) under vacuum.

■

Andrey Turshatov: 0000-0002-8004-098X Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS

■

REFERENCES

A.T. gratefully acknowledges the financial support from the Professorial Recruitment Initiative of the Helmholtz Association for B.S. Richards, as well as the Helmholtz program Science and Technology of Nanosystems (STN). N.K gratefully acknowledges the financial support from German Academic Exchange Service (DAAD). The authors are grateful to Wolfgang Arbogast for technical expertise in DSC and SEC.

(1) Monguzzi, A.; Tubino, R.; Hoseinkhani, S.; Campione, M.; Meinardi, F. Low Power, Non-Coherent Sensitized Photon Upconversion: Modelling and Perspectives. Phys. Chem. Chem. Phys. 2012, 14, 4322−4332. (2) Schulze, T. F.; Schmidt, T. W. Photochemical Upconversion: Present Status and Prospects for Its Application to Solar Energy Conversion. Energy Environ. Sci. 2015, 8, 103−125. (3) Li, C.; Koenigsmann, C.; Deng, F.; Hagstrom, A.; Schmuttenmaer, C. A.; Kim, J.-H. Photocurrent Enhancement from Solid-State Triplet−Triplet Annihilation Upconversion of LowIntensity, Low-Energy Photons. ACS Photonics 2016, 3, 784−790. (4) Khnayzer, R. S.; Blumhoff, J.; Harrington, J. A.; Haefele, A.; Deng, F.; Castellano, F. N. Upconversion-Powered Photoelectrochemistry. Chem. Commun. 2012, 48, 209−211. (5) Borjesson, K.; Dzebo, D.; Albinsson, B.; Moth-Poulsen, K. Photon Upconversion Facilitated Molecular Solar Energy Storage. J. Mater. Chem. A 2013, 1, 8521−8524. (6) Wohnhaas, C.; Mailänder, V.; Dröge, M.; Filatov, M. A.; Busko, D.; Avlasevich, Y.; Baluschev, S.; Miteva, T.; Landfester, K.; Turshatov, A. Triplet−Triplet Annihilation Upconversion Based Nanocapsules for Bioimaging Under Excitation by Red and Deep-Red Light. Macromol. Biosci. 2013, 13, 1422−1430. (7) Liu, Q.; Yang, T.; Feng, W.; Li, F. Blue-Emissive Upconversion Nanoparticles for Low-Power-Excited Bioimaging in Vivo. J. Am. Chem. Soc. 2012, 134, 5390−5397. (8) Wang, W.; Liu, Q.; Zhan, C.; Barhoumi, A.; Yang, T.; Wylie, R. G.; Armstrong, P. A.; Kohane, D. S. Efficient Triplet−Triplet Annihilation-Based Upconversion for Nanoparticle Phototargeting. Nano Lett. 2015, 15, 6332−6338. (9) Borisov, S. M.; Larndorfer, C.; Klimant, I. Triplet−Triplet Annihilation-Based Anti-Stokes Oxygen Sensing Materials with a Very Broad Dynamic Range. Adv. Funct. Mater. 2012, 22, 4360−4368. (10) Lee, S. H.; Lott, J. R.; Simon, Y. C.; Weder, C. Melt-Processed Polymer Glasses for Low-Power Upconversion via Sensitized TripletTriplet Annihilation. J. Mater. Chem. C 2013, 1, 5142−5148. (11) Lee, S. H.; Ayer, M. A.; Vadrucci, R.; Weder, C.; Simon, Y. C. Light Upconversion by Triplet-Triplet Annihilation in Diphenylanthracene-Based Copolymers. Polym. Chem. 2014, 5, 6898−6904. (12) Lee, S. H.; Thévenaz, D. C.; Weder, C.; Simon, Y. C. Glassy Poly(methacrylate) Terpolymers with Covalently Attached Emitters and Sensitizers for Low-Power Light Upconversion. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1629−1639. (13) Merkel, P. B.; Dinnocenzo, J. P. Low-Power Green-to-Blue and Blue-to-UV Upconversion in Rigid Polymer Films. J. Lumin. 2009, 129, 303−306. (14) Raišys, S.; Kazlauskas, K.; Juršeṅ as, S.; Simon, Y. C. The Role of Triplet Exciton Diffusion in Light-Upconverting Polymer Glasses. ACS Appl. Mater. Interfaces 2016, 8, 15732−15740. (15) Islangulov, R. R.; Lott, J.; Weder, C.; Castellano, F. N. Noncoherent Low-Power Upconversion in Solid Polymer Films. J. Am. Chem. Soc. 2007, 129, 12652−12653.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b12625. Scheme of the TTA-UC process, characteristics of polymers, TTA-UC emission for POS polymers, scheme of the optical setup, decays of phosphorescence and TTA-UC, parameters of fitting, results of 1H MAS-SSNMR experiments for different polymers, results of 13C MAS-SS-NMR experiments for POS12 host and different temperatures (PDF)

■

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. 8285


Research Article

ACS Applied Materials & Interfaces (16) Singh-Rachford, T. N.; Lott, J.; Weder, C.; Castellano, F. N. Influence of Temperature on Low-Power Upconversion in Rubbery Polymer Blends. J. Am. Chem. Soc. 2009, 131, 12007−12014. (17) Marsico, F.; Turshatov, A.; Peköz, R.; Avlasevich, Y.; Wagner, M.; Weber, K.; Donadio, D.; Landfester, K.; Baluschev, S.; Wurm, F. R. Hyperbranched Unsaturated Polyphosphates as a Protective Matrix for Long-Term Photon Upconversion in Air. J. Am. Chem. Soc. 2014, 136, 11057−11064. (18) Monguzzi, A.; Mauri, M.; Bianchi, A.; Dibbanti, M. K.; Simonutti, R.; Meinardi, F. Solid-State Sensitized Upconversion in Polyacrylate Elastomers. J. Phys. Chem. C 2016, 120, 2609−2614. (19) Monguzzi, A.; Mauri, M.; Frigoli, M.; Pedrini, J.; Simonutti, R.; Larpent, C.; Vaccaro, G.; Sassi, M.; Meinardi, F. Unraveling Triplet Excitons Photophysics in Hyper-Cross-Linked Polymeric Nanoparticles: Toward the Next Generation of Solid-State Upconverting Materials. J. Phys. Chem. Lett. 2016, 7, 2779−2785. (20) Thevenaz, D. C.; Monguzzi, A.; Vanhecke, D.; Vadrucci, R.; Meinardi, F.; Simon, Y. C.; Weder, C. Thermoresponsive Low-Power Light Upconverting Polymer Nanoparticles. Mater. Horiz. 2016, 3, 602−607. (21) Lobez, J. M.; Swager, T. M. Radiation Detection: Resistivity Responses in Functional Poly(Olefin Sulfone)/Carbon Nanotube Composites. Angew. Chem., Int. Ed. 2010, 49, 95−98. (22) Callan, J. F.; Fawcett, A. H.; Malcolm, R. K. The Effect of Tacticity on the Conformational Properties of Poly(1-olefin sulfone)s. J. Polym. Res. 2008, 15, 107−113. (23) Matsumoto, A.; Lee, S.; Okamura, H. Molecular Design of Diene Monomers Containing an Ester Functional Group for the Synthesis of Poly(diene sulfone)s by Radical Alternating Copolymerization with Sulfur Dioxide. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1000−1009. (24) Ito, F.; Kogasaka, Y.; Yamamoto, K. Fluorescence Spectral Changes of Perylene in Polymer Matrices during the Solvent Evaporation Process. J. Phys. Chem. B 2013, 117, 3675−3681. (25) Cheng, Y. Y.; Fückel, B.; Khoury, T.; Clady, R. G. C. R.; Tayebjee, M. J. Y.; Ekins-Daukes, N. J.; Crossley, M. J.; Schmidt, T. W. Kinetic Analysis of Photochemical Upconversion by Triplet−Triplet Annihilation: Beyond Any Spin Statistical Limit. J. Phys. Chem. Lett. 2010, 1, 1795−1799. (26) Monguzzi, A.; Mezyk, J.; Scotognella, F.; Tubino, R.; Meinardi, F. Upconversion-Induced Fluorescence in Multicomponent Systems: Steady-State Excitation Power. Threshold. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 78, 195112. (27) Leisen, J.; Gomez, I. J.; Roper, J. A.; Meredith, J. C.; Beckham, H. W. Spatially Resolved Solid-State 1H NMR for Evaluation of Gradient-Composition Polymeric Libraries. ACS Comb. Sci. 2012, 14, 415−424. (28) Ruben, G. C.; Stockmayer, W. H. Evidence for Helical Structures in Poly(1-olefin sulfones) by Transmission Electron Microscopy. Proc. Natl. Acad. Sci. U. S. A. 1992, 89, 7991−7995. (29) Dass, N. N.; Date, R. W.; Fawcett, A. H.; McLaughlin, J. D.; Sosanwo, O. A. Recognition of a New Type of Main Chain LiquidCrystalline Polymer: Poly(1-olefin sulfones). Macromolecules 1993, 26, 4192−4195. (30) de Mello, J. C.; Wittmann, H. F.; Friend, R. H. An Improved Experimental Determination of External Photoluminescence Quantum Efficiency. Adv. Mater. 1997, 9, 230−232. (31) Faulkner, D. O.; McDowell, J. J.; Price, A. J.; Perovic, D. D.; Kherani, N. P.; Ozin, G. A. Measurement of Absolute Photoluminescence Quantum Yields Using Integrating Spheres − Which Way to Go? Laser & Photonics Reviews 2012, 6, 802−806.

8286


Room-Temperature High-Efficiency Solid-State ... - ACS Publications

Recommend Documents