We test the potential of resonance energy transfer to enhance the performance of conjugated copolyelectrolyte donor–acceptor luminescent solar concentrators immobilised within a photoactive organic–inorganic ureasil waveguide.</p

Arlt, J

Blayo, C

Burrows, HD

Evans, RC

Marques, AT

Meazzini, I

Scherf, U

We test the potential of resonance energy transfer to enhance the performance of conjugated copolyelectrolyte donor–acceptor luminescent solar concentrators immobilised within a photoactive organic–inorganic ureasil waveguide.
 The development of an efficient luminescent solar concentrator (LSC), with minimised optical losses, requires careful consideration of its principal constituting materials, a waveguide and a luminophore, in tandem. Here, a series of LSCs are fabricated utilising a poly(fluorene- alt -phenylene) copolymer containing on-chain perylenediimide (PDI) chromophore units as the luminophore ( PBS-PFP-PDI ) immobilised within a poly(oxyalkylene)/siloxane organic–inorganic hybrid, known as a ureasil, as the waveguide. PBS-PFP-PDI and the ureasil both function as photoactive components, offering the possibility of energy transfer between the ureasil host and/or the PBS-PFP donor chains to the PDI acceptor, leading to reduced re-absorption losses and harvesting a broader wavelength range of the solar spectrum. A combination of studies using UV/vis absorption, Fourier transform infrared, steady-state and time-resolved photoluminescence spectroscopies revealed that the branching of the ureasil framework influences the packing of the polymer chains, with the tri-podal ureasil structure facilitating improved dispersion of the PBS-PFP-PDI chains, while the linear di-ureasil structure promotes more intimate mixing of the PBS-PFP-PDI and the ureasil. Picosecond time-correlated single photon counting measurements showed that strong spectral overlap, combined with efficient electronic coupling results in efficient excitation energy transfer from the ureasil to emissive trap sites localised on the PBS-PFP unit. This process inhibits subsequent energy transfer to the PDI chromophore, but leads to high solid-state photoluminescence quantum yields of &gt;50%. The optical efficiency of the PBS-PFP-PDI–ureasil composites as LSCs was evaluated under AM1.5G solar simulated light delivering values of up to 5.6% using a scattering background, which could be boosted to 13.1% by increasing the percentage of PDI units per PBS-PFP chains using a model system. The results demonstrate that consideration of the combined photophysical properties of the luminophore and the waveguide are crucial to the design of next generation LSCs. </p

Apollo (Cambridge)

1  Electronic Supplementary Information   Ureasil Organic-Inorganic Hybrids as Photoactive Waveguides for Conjugated Polyelectrolyte Luminescent Solar Concentrators Ilaria Meazzini,a Camille Blayo,a Jochen Arlt,b Ana-Teresa Marques,cd Ullrich Scherf,d Hugh D. Burrowsc and Rachel C. Evansa, e a School of Chemistry, Trinity College Dublin, Dublin 2, Ireland.  b Collaborative Optical Spectroscopy, Micromanipulation and Imaging Centre (COSMIC) and SUPA, School of Physics and Astronomy, King’s Buildings, University of Edinburgh, EH9 3JZ, U.K. c Centro de Química, Chemistry Department, University of Coimbra, 3004-535 Coimbra, Portugal. d Macromolecular Chemistry Group (buwmacro) and Institute for Polymer Technology, Bergische Universität Wuppertal, Wuppertal, Germany. e Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, U.K. Email: rce26@cam.ac.uk   2  Table of Contents 1. Instrumentation 2. Steady-State Photoluminescence Studies 3. Fourier Transform Infrared (FTIR) Spectroscopy in the Amide I Region 4. Picosecond (ps) Time-Correlated Single Photon Counting (TCSPC) Studies 5. Performance as Luminescent Solar Concentrators (LSCs) 6. References    3  1. Instrumentation  Fourier transform infrared (FTIR) measurements were carried out on a Perkin-Elmer spectrum 100 FTIR spectrometer at room temperature and collected over a range of 400-4000 cm-1 by averaging 64 scans at a resolution of 4 cm-1. The grounded samples (2 mg) were mixed with potassium bromide (175 mg) and pressed into pellets. The contributions to the Amide I band (1600-1800 cm-1) were obtained through spectral deconvolution using Gaussian band fitting in Origin 8.0s (Microcal).  Steady-state photoluminescence (PL) measurements were carried on a Fluorolog-3 spectrophotometer (Horiba Jobin Yvon), using the front-face configuration for solid-state samples. Emisson and excitation slits were fixed at 0.75 nm. Photoluminescence quantum yields were measured in a F-3018 integrating sphere accessory mounted on a FluoroMax-4 spectrophotometer (Horiba Jobin Yvon) and the values reported are the mean of three repeat measurements. The method is accurate to within 10%. Emission and excitation spectra were corrected for the wavelength response of the system and the intensity of the lamp profile over the excitation range, respectively, using correction factors supplied by the manufacturer. UV/Vis absorption spectra were recorded using a Perkin Elmer Lambda 1050 UV/Vis scanning spectrometer. Fluorescence decays were measured using the picosecond time-correlated single photon counting (TCSPC) method at the Collaborative Optical Spectroscopy, Micromanipulation and Imaging Centre (COSMIC), University of Edinburgh, U.K. The excitation source was the second harmonic of the pulse-picked output of a Ti-Sapphire femtosecond laser system (Coherent, 10 W Verdi and Mira Ti-Sapphire), delivering pulses of ≈200 fs at 4.75 MHz repetition rate. Fluorescence decays were measured using an Edinburgh Instruments spectrometer equipped with TCC900 photon counting electronics. The instrument response of the system was ≈90 ps full-width-half-maximum (FWHM). The decay curves were analysed using a standard iterative reconvolution method, assuming a multi-exponential decay function. Reconvolution and fitting of the fluorescence decays were carried out using Globals WE software package. The quality of fit was judged on the basis of the reduced chi-square statistic, χ2, and the randomness of residuals.   4  2. Steady-State Photoluminescence Studies     Figure S1. Excitation spectra of (a) DU-CPE-0 and (c) TU-CPE-0 at different emission wavelengths. Emission spectra of (b) TU-CPE-0 at different excitation wavelengths.    Figure S2. Emission spectra of (a) DU-CPE-02, (b) DU-CPE-04, (c) TU-CPE-02 and (d) TU-CPE-04 at different excitation wavelengths.   5   Figure S3. Excitation spectra of (a) DU-CPE-02, (b) DU-CPE-04, (c) TU-CPE-02 and (d) TU-CPE-04 at different emission wavelengths.   3. FTIR Spectroscopy in the Amide I Region     Figure S4. FTIR spectra and corresponding Gaussian curve-fits of the Amide I region of (a) DU-CPE-02, (b) DU-CPE-04, (c) DU-CPE-08, (d) TU-CPE-02, (e) TU-CPE-04 and (f) TU-CPE-08.   6  Table S1. Results of Gaussian curve fitting of the Amide I band of DU-CPE-x and TU-CPE-x, showing the peak position, area and % contribution for each component resolved.  Sample ID Peak 1 /cm-Contribution (%) Peak 2 /cm-1 Contribution (%) Peak 3 /cm-1 Contribution (%) Peak 4 /cm-1 Contribution (%) DU-CPE-0  1637.1 (21.8)  1663.3 (47.9)  1715.4 (30.3)   DU-CPE-02  1636.8 (21.1)  1663.3 (49.3)  1717.4 (29.6)   DU-CPE-04  1637.0 (21.7)  1663.2 (52.7)  1716.5 (25.6)   DU-CPE-08  1637.0 (20.7)  1662.7 (51.2)  1715.2 (28.1)   TU-CPE-0  1632.1 (22.8)  1656.2 (46.7)  1692.7 (28.6)  1770.6 (1.9) TU-CPE-02  1631.9 (23.3)  1656.2 (47.3)  1692.4 (27.6)  1770.9 (1.8)  TU-CPE-04  1631.9 (23.0)  1656.0 (49.0)  1693.6 (26.1)  1770.6 (1.9)  TU-CPE-08  1631.9 (23.7)  1656.4 (48.8)  1693.8 (25.6)  1770.8 (1.9)    4. Picosecond (ps) Time-Correlated Single Photon Counting (TCSPC) Studies  4.1 Fitting procedure Fluorescence decays were measured for PBS-PFP-PDI in solution (1:1 v/v water:1,4-dioxane) and for DU-CPE-x and TU-CPE-x samples upon excitation at 370 nm and detection of the emission at 420 nm, 500 nm and 600 nm. For all samples, the decay curves displayed complex multi-exponential behaviour, requiring either two, three or four components to fit the experimental data. The form of the theoretical multi-exponential decay was fitted using the following model:  ! " = $%exp	(−" ,%)% (1) where αi and τi are the pre-exponential factor and characteristic lifetime for component i, respectively. This theoretical expression takes into account the response of a sample upon an infinitely sharp excitation, also known as a δ-function.4 In this model, the intensity is assumed to decay as the sum of individual single exponential decays. When studying one fluorophore presenting a complex decay, it is generally acceptable to consider that such fluorophore presents the same radiative decay rate in each environment. Thus, in this case αi represents the fraction of molecules in each environment at t = 0.5 7  The average fluorescence lifetime <τ> is calculated from:  < , >= $%,%0$%,% (2) In practise however, the excitation pulse is not infinitely short and thus the sample does not only decay starting directly after the pulse. Thus, the theoretical multi-exponential decay model (1) is reconvoluted with the instrumental response function (IRF) (which includes the width of the excitation pulse and possible electronic responses of the instrument) using the following integral:  !′ " = 1 " ′ ! " − " ′ 2"′34 (3) where E(t) is the excitation pulse and I(t) is the theoretical decay model (1). This expression states that the experimentally-measured intensity at time t is given by the sum of the intensities expected for all δ-function excitation pulses that occur until time t, if the excitation pulse is imagined to be comprised as a series of δ-functions with different amplitudes.6 This model is then fit to the measured decay through the method of non-linear least squares analysis (NLLS), which tests if the used model is consistent with the data. This is achieved by varying αi and τi until the goodness-of-fit parameter, χ2 is at a minimum. χ2 is described by:  50 = 6% − 7%86%009%:; (4)  where yi is the measured data, n is the number of data points and fic is the calculated fit.   The quality of the NLLS analysis was also judged based on the randomness of the weighted residuals plot.     8  4.2 Supplementary Decay Curves and Fits    Figure S5. Emission decay curve (solid black line) and corresponding fit (solid red line) for TU-CPE-08 (λex = 466 nm, λem= 600 nm). The fitted decay times (τi), the pre-exponential coefficients (αi), chi-squared (χ2), weighted residuals and instrument response function (IRF, dotted blue line) are also shown.   9  Table S2. Photoluminescence lifetimes (τi), pre-exponential coefficients (αi), and chi squared (χ2) values obtained from fitting of the emission decays (λex = 370 nm) at λem = 420 and 500 nm.   λem = 420 nm Sample τ1 (ns)  τ2 (ns) τ3 (ns) τ4 (ns) α1  α2  α3  α4 χ2           CPE 0.026±0.001 0.553±0.002 1.072±0.020  -0.899±0.001 0.947±0.001 0.053±0.001  1.14           DU-CPE-0  0.47±0.01 2.56±0.04 10.08±0.12  0.75 ±0.02 0.20 ± 0.01 0.05 ± 0.01 1.55 DU-CPE-02 0.029±0.005 0.538±0.002 1.640±0.037  -0.281±0.004 0.982±0.002 0.018±0.001  1.03 DU-CPE-04  0.537±0.002 1.545±0.068  0.990±0.002 0.010±0.001   1.32 DU-CPE-08  0.548±0.002 1.224±0.045  0.983±0.002 0.017±0.001   1.20           TU-CPE-0  0.522±0.030 4.204±0.052 12.740±0.089  0.474±0.005 0.378±0.003 0.148±0.001 1.43 TU-CPE-02  0.513±0.003 1.050±0.029 8.103±0.025  0.943±0.003 0.052±0.002 0.005±0.001 1.12 TU-CPE-04  0.544±0.003 5.396±0.187   0.995±0.003 0.005±0.001  1.25 TU-CPE-08  0.550±0.003 3.223±0.141   0.996±0.003 0.004±0.001  1.308  λem = 500 nm  Sample τ1 (ns)  τ2 (ns) τ3 (ns) τ4 (ns) α1  α2  α3  α4 χ2 CPE 0.034±0.003 0.582±0.002 1.364±0.028  -0.491±0.002 0.967±0.016 0.033±0.001  1.07           DU-CPE-0  0.39 ± 0.02 2.79 ± 0.05 10.90 ± 0.14  0.63 ± 0.03 0.29 ± 0.02 0.07 ± 0.02 1.66 DU-CPE-02 0.041±0.003 0.556±0.004 1.431±0.025 6.980±0.191 -0.184±0.001 0.941±0.001 0.052±0.001 0.007±0.001 0.99 DU-CPE-04 0.022±0.003 0.597±0.004 4.106±0.116  -0.782±0.002 0.989±0.001 0.011±0.001  1.25 DU-CPE-08 0.024±0.003 0.618±0.004 3.624±0.112  -0.732±0.002 0.991±0.002 0.009±0.001  1.18           TU-CPE-0  0.792±0.030 4.845±0.052 14.213±0.102  0.425±0.005 0.431±0.003 0.144±0.001 1.24 TU-CPE-02  0.593±0.006 1.904±0.037 10.390±0.167  0.873±0.004 0.112±0.002 0.015±0.001 1.32 TU-CPE-04  0.563±0.003 2.125±0.087 9.297±0.204  0.957±0.002 0.030±0.001 0.013±0.001 1.49 TU-CPE-08  0.605±0.007 1.504±0.030 8.819±0.240  0.840±0.004 0.153±0.003 0.007±0.001 1.32             10    Figure S6. Emission decay curves (solid black lines) and corresponding fits (solid red lines) for (a) DU-CPE-02, (b) DU-CPE-04 and (c) DU-CPE-08 upon excitation at 370 nm (λem = 500 nm). The fitted decay times (τi), the pre-exponential coefficients (αi), chi-squared (χ2), weighted residuals and instrument response function (IRF, dotted blue line) are also shown.           11   Figure S7. Emission decay curves (solid black lines) and corresponding fits (solid red lines) for (a) TU-CPE-02, (b) TU-CPE-04 and (c) TU-CPE-08 upon excitation at 370 nm (λem = 500 nm). The fitted decay times (τi), the pre-exponential coefficients (αi), chi-squared (χ2), weighted residuals and instrument response function (IRF, dotted blue line) are also shown.   Figure S8. Optical power spectrum of the solar simulator (AM1.5G). 12  5. References  [1] H. D. Burrows, V. M. M. Lobo, J. Pina, M. L. Ramos, J. S. de Melo, A. J. M. Valente, M. J. Tapia, S. Pradhan and U. Scherf, Macromolecules, 2004, 37, 7425–7427. [2] A. T. Marques, H. D. Burrows, J. S. Seixas de Melo, A. J. Valente, L. L. Justino, U. Scherf, E. Fron, S. Rocha, J. Hofkens, E. W. Snedden and A. P. Monkman, J. Phys. Chem. B, 2012, 116, 7548–7559. [3] I. Meazzini, N. Willis-Fox, C. Blayo, J. Arlt, S. Clément and R. C. Evans, J. Mater. Chem. C, 2016, 4, 4049-4059. [4] J. R. Lakowicz, in Principles of Fluorescence Spectroscopy, Springer, 2006, p. 99. [5] J. R. Lakowicz, in Principles of Fluorescence Spectroscopy, Springer, 2006, p. 142. [6] J. R. Lakowicz, in Principles of Fluorescence Spectroscopy, Springer, 2006, p. 106.   

English

Ureasil organic–inorganic hybrids as photoactive waveguides for conjugated polyelectrolyte luminescent solar concentrators

The development of an efficient luminescent solar concentrator (LSC), with minimised optical losses, requires careful consideration of its principal constituting materials, a waveguide and a luminophore, in tandem. Here, a series of LSCs are fabricated utilising a poly(fluorene-alt-phenylene) copolymer containing on-chain perylenediimide (PDI) chromophore units as the luminophore (PBS-PFP-PDI) immobilised within a poly(oxyalkylene)/siloxane organic-inorganic hybrid, known as a ureasil, as the waveguide. PBS-PFP-PDI and the ureasil both function as photoactive components, offering the possibility of energy transfer between the ureasil host and/or the PBS-PFP donor chains to the PDI acceptor, leading to reduced re-absorption losses and harvesting a broader wavelength range of the solar spectrum. A combination of studies using UV/vis absorption, Fourier transform infrared, steady-state and time-resolved photoluminescence spectroscopies revealed that the branching of the ureasil framework influences the packing of the polymer chains, with the tri-podal ureasil structure facilitating improved dispersion of the PBS-PFP-PDI chains, while the linear di-ureasil structure promotes more intimate mixing of the PBS-PFP-PDI and the ureasil. Picosecond time-correlated single photon counting measurements showed that strong spectral overlap, combined with efficient electronic coupling results in efficient excitation energy transfer from the ureasil to emissive trap sites localised on the PBS-PFP unit. This process inhibits subsequent energy transfer to the PDI chromophore, but leads to high solid-state photoluminescence quantum yields of &gt;50%. The optical efficiency of the PBS-PFP-PDI-ureasil composites as LSCs was evaluated under AM1.5G solar simulated light delivering values of up to 5.6% using a scattering background, which could be boosted to 13.1% by increasing the percentage of PDI units per PBS-PFP chains using a model system. The results demonstrate that consideration of the combined photophysical properties of the luminophore and the waveguide are crucial to the design of next generation LSCs

Meazzini, Ilaria

Blayo, Camille

Arlt, Jochen

Marques, Ana-Teresa

Scherf, Ullrich

Burrows, Hugh D.

Evans, Rachel C.

Edinburgh Research Explorer

Ureasil organic-inorganic hybrids as photoactive waveguides for conjugated polyelectrolyte luminescent solar concentrators

Ilaria Meazzini

Camille Blayo

Jochen Arlt

Ana-Teresa Marques

Ullrich Scherf

Hugh D. Burrows

Rachel C. Evans

Crossref

Materials Chemistry Frontiers

https://www.repository.cam.ac.uk/bitstream/1810/271156/1/MCF-2017-Meazzinietal-accepted.pdf

Ureasil organic-inorganic hybrids as photoactive waveguides for conjugated polyelectrolyte luminescent solar concentrators

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Apollo (Cambridge)

Edinburgh Research Explorer

Edinburgh Research Explorer

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