Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2017.
Supporting Information
for Advanced Optical Materials, DOI: 10.1002/adom.201700523
All-Polymer Photonic Microcavities Doped with Perylene
Bisimide J-Aggregates
Paola Lova, Vincenzo Grande, Giovanni Manfredi,
Maddalena Patrini, Stefanie Herbst, Frank Würthner,* and
Davide Comoretto*
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Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2016.
Supporting Information
All-Polymer Photonic Microcavities Doped with Perylene Bisimide J-Aggregates
Paola Lova, Vincenzo Grande, Giovanni Manfredi, Maddalena Patrini, Stefanie Herbst, Frank Würthner*, Davide Comoretto*
Dr. P. Lova, G. Manfredi, Prof. Dr. D. Comoretto
Dipartimento di Chimica e Chimica industriale, Università degli studi di Genova, Via Dodecaneso 31, 16146, Genova, Italy
DC: davide.comoretto@unige.it
Prof. Dr. M. Patrini
Dipartimento di Fisica, Università degli studi di Pavia, Via A. Bassi, 6, 27100 Pavia, Italy
Dr. V. Grande, S. Herbst, Prof. Dr. F. Würthner
Institut für Organische Chemie, Universität Würzburg, Am Hubland 97074 Würzburg, Germany and Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI), Theodor-Boveri-Weg, 97074 Würzburg (Germany)
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Figure S1 shows the absorption spectra of PEH-PBI in the monomer state (in toluene) and the
formation of the J-aggregate in toluene/n-hexane mixtures. The spectra support that the change in the absorption band is due to the formation of a J-aggregate, which forms at a critical solvent composition instantaneously and which exhibits a nearly 70 nm redshifted absorption band. The slight shift of the monomer spectrum is due to solvatochromism as expected for binary solvents mixtures.
Figure S1: (a) PEH-PBI absorbance spectra in toluene (red line), n-hexane (blue line) and
toluene/n-hexane mixtures (21.0 µM, T = 25 °C). (b) The formation of the aggregate monitored at 630 nm) indicates that aggregation occurs in the range of 60 – 100 %v/v of n-hexane content.
The red line is only a visual guide for the eye. In the inset of Figure S1(a), an image of the samples under ambient light is shown for solutions in toluene (red solution, left) to n-hexane (blue solution, right).
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Figure S2 shows the nanofibers of the PEH-PBI J-aggregate as observed by atomic force
microscopy. The diameter of the fibers is consistent with the bundling of the J-aggregate fibers.
Figure S2: AFM images of a spin coated PEH-PBI solution in n-hexane (20 µM) onto Si-wafer,
with different enlargements (a and b respectively). (c) Height profile along the dotted yellow line in Figure S2a.
FTIR investigations in Figure S3 show the formation of intermolecular hydrogen bonds within the J-aggregate. In comparison with the IR spectrum in chloroform solution, in which the compound is present in a monomeric state, the spectrum in n-hexane shows a redshifted N-H stretching at 3173 cm-1, due to the formation of hydrogen bonds. Accordingly, the imide C=O stretching signal at 1698 cm-1 decreases intensity while an additional C=O stretching peak is observed at lower energy (1678 cm-1). Furthermore, the hydrogen bonded structure has also been observed in the soft crystalline state, in good agreement with the characterization previously reported.[1]
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Figure S3: FTIR spectra of PEH-PBI as soft crystal (red line), in chloroform solution as
monomer (black line, 2.0 mM) and in n-hexane as J-aggregate (blue line, 0.3 mM). The shifts of the N-H and C=O stretching vibrations upon aggregation in solution indicate the formation of the hydrogen-bonded supramolecular polymer, in good analogy with the stretching signals in the solid state. The arrows indicate the modifications in the N-H and C=O stretchings involved in the aggregation process. For the measurement in n-hexane, the signal of the solvent between 2800 – 3000 cm-1 has been subtracted from the spectra.
Figure S4 shows the complex refractive index (n+ik) for polyacrylic acid (PAA), amorphous
polypropylene (aPP) and of its blend with PEH-PBI J-aggregates. PAA has a relatively high
refractive index among commodity polymers (comparable to that of polyvinylalcohol, PVA) but
it is easier to process than cellulose acetate that is often employed for the fabrication of planar
microcavities.[2] Amorphous polypropylene is instead a low refractive index polymer particularly
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Figure S4: Complex refractive index n + ik (n, upper panel; k, lower panel) dispersion of PAA
(green line), aPP (black line), and of its composites containing PEH-PBI J-aggregates (red lines).
The dispersion of the complex refractive indexes can be analytically reproduced by a combination of Cauchy dispersion, Urbach tail and a background due to and one high energy residual pole.[3] PAA and aPP do not show any significant imaginary part in the considered spectral range, while the PEH-PBI J-aggregate blended in aPP shows an absorption band that has been modeled through a Gaussian oscillator accounting for the J-aggregate strong absorption. This oscillator obviously modifies the refractive index lineshape with the typical dispersive feature. The overall spectral dispersion is given by:
√ ∞
6 where [ ( ) ( ) ] ∫ ( ) ∞ √ ( ) (S2)
All fitting parameters are reported in Table S1.
Table S1. Fitting parameters for the complex refractive index of different materials used.
A B [m2] C [m4] ∞ (eV-1) (eV) AG EG (eV) BG (eV) Ep (eV) Ap (eV2) PAA 1.423 0.0016638 3.0222e-5 0.0323 - - - 7.6553 12.32 aPP 1.427 0.0031512 1.8675e-5 0 - - - 9.7451 9.4001
PEH-PBI:aPP 1.438 0.0003916 6.039 e-4 0.1219 3.2e-2 1.1716 3.85 0.00446 1.9689 0.12665 - -
Figure S5a shows the angular dispersion of the microcavity transmittance spectra for both for P-
and S-polarizations. As expected, the width of the PBG decreases upon increasing the incidence
angle for P-polarization only. This supports a good optical quality of the spun-cast microcavities.
The data shown in Figure S5b were modelled using the refractive index dispersion of materials
as input, and allow to retrieve the layer thicknesses. The model perfectly reproduces
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Figure S5: Experimental (left panels) and calculated (right panels) angle resolved transmittance
spectra of the microcavity for P-polarization (top panels) and S-polarization (bottom panels).
Figure S6a shows the PL ratio spectra of the microcavity as a function of the detection angle.
The ratio spectra are obtained by dividing the PL spectra of the microcavity by the corresponding
PL spectra of Reference 1 (the PEH-PBI J-aggregates blended in aPP) for the different detection
angles). We notice that the ratio decreases with increasing the detection angle because the
spectral overlap between the cavity mode with the PL spectrum of the emitter is progressively
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Figure S6: a) spectra and (b) their contour plot as a function of the collection angle in the range 0 ° – 60 °.
Figure S7 shows the calculated optical spectra (transmittance and reflectance) for the
microcavity and the DBR mirrors composing it. These reflectance spectra have been used to
calculate the radiative rate enhancement (Ge) of the microcavity. Indeed, the reflectance spectra
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Figure S7: Calculated microcavity transmittance (black line, see also Figure 2), and Reflectance
for top (green line) and bottom (red line) microcavity mirrors.
The absence of a radiative rate enhancement in the microcavity (details are described into the
main text) does not stimulate to discuss the enhancement effect in details. However, for clarity,
we report here the characterization usually adopted in these cases.[4]
Starting from Equation 1 in the main text, the overall rate enhancement for a microcavity can be
evaluated step-by-step from the analysis of the peak rate enhancement factor 𝐺 at normal incidence detection (= 0 °), as described in the manuscript. In addition, we can easily derive 𝐺 , that is the ratio between the PL intensity of the microcavity ( ) and of the bare emitter
( ) at the cavity mode wavelength for different detection angles ():[5]
𝐺 ( ) ( )
( ) (S3)
( ) and ( ) are reported in Figure S8a while 𝐺 ( ) is shown in Figure S8b for
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from the reference sample in the interval 0 ° – 42 °. For higher angles, the cavity mode falls
outside the J-aggregate emission spectrum, and the signal for the microcavity becomes lower
than for the reference (see Figure S8a). The ratio between the two signals, 𝐺 ranges from ~ 5 at ° to ~ 1 at ° and, as expected, it is less than 1 for collection angles larger than 42 ° (Figure S8b). These data are in agreement with the theoretical ratio calculated from
Equation 1, and with literature data.[4-5]
To assess the effect of the microcavity on the emission rate, the enhancement over the entire
spectrum (𝐺 ) can be evaluated, that is the relative brightness of the emitter in the microcavity with respect to the reference. According to literature references,[4-5] assuming a Gaussian natural
emission, and considering the spectral width of the cavity and of reference PL spectrum, at
normal incidence, 𝐺 can be defined from 𝐺 as:
𝐺 𝐺 √
° (S4)
being = 6.7 nm the width of the microcavity emission and = 50 nm the width of the J-aggregated reference film, and 𝐺 = 5. We can then estimate 𝐺 ~ 1. Experimentally 𝐺 (θ) is defined by the ratio between the PL spectra of the microcavity and those of the reference
integrated on the overall spectral range of the PEH-PBI emission: [5]
𝐺 ( ) ∫ ( )
∫ ( ) (S5)
Figure S8c shows that the values of the integrated photoluminescence spectra both for the
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for the microcavity for all collection angles. The experimental value of 𝐺 ( ) calculated from Equation S5 (and reported in Figure S8d), shows values ~ 0.4 in the range of detection angles 0 –
45 °, when the cavity mode overlaps the maximum emission intensity of the J-aggregate (see
also Figure 4c and Supporting Information Figure S6). For higher angles, the calculation does
not apply because the PBG is moving toward a spectral region where the PL of J-aggregate is
negligible.
Figure S8: a) Peak PL intensities for the microcavity (red) and the reference PEH-PBI
J-aggregate film (blue). b) 𝐺 (Equation S3). c) Wavelength integrated PL for PEH-PBI J-aggregate microcavity (red) and reference film (blue) for different collection angles. d) 𝐺 (Equation S5).
From these data, we can then evaluate the total emission enhancement factor calculated over the
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𝐺 ∫ ∫ ( )
∫ ∫ ( ) (S6)
We found, 𝐺 = 0.39. This value, even though lower than 1 (i.e. no rate enhancement observed), is in agreement data previously reported on microcavities where a fluorescent
conjugated polymer is asymmetrically confined between a high dielectric contrast inorganic
DBR and a metallic mirror.[5]
Supporting Information References
[1] S. Herbst, B. Soberats, P. Leowanawat, M. Lehmann, F. Würthner, Angew. Chem. Int.
Ed. 2017, 56, 2162.
[2] a) L. Fornasari, F. Floris, M. Patrini, D. Comoretto, F. Marabelli, Phys. Chem. Chem.
Phys. 2016, 18, 14086; b) G. Manfredi, C. Mayrhofer, G. Kothleitner, R. Schennach, D.
Comoretto, Cellulose 2016, 23, 2853; c) R. J. Knarr III, G. Manfredi, E. Martinelli, M. Pannocchia, D. Repetto, C. Mennucci, I. Solano, M. Canepa, F. Buatier de Mongeot, G. Galli, D. Comoretto, Polymer 2016, 84, 383; d) S. Gazzo, G. Manfredi, R. Poetzsch, Q. Wei, M. Alloisio, B. Voit, D. Comoretto, J. Polym. Sci. B: Polym. Phys. 2016, 54, 73; e) G. Manfredi, P. Lova, F. Di Stasio, R. Krahne, D. Comoretto, ACS Photonics submitted; f) S. Pirotta, M. Patrini, M. Liscidini, M. Galli, G. Dacarro, G. Canazza, G. Guizzetti, D. Comoretto, D. Bajoni, Appl. Phys. Lett. 2014, 104, 4051111.
[3] WVASE32® software, by J.A. Woollam Co.
[4] E. F. Schubert, N. E. J. Hunt, M. Micovic, R. J. Malik, D. L. Sivco, A. Y. Cho, G. J. Zydzik, Science 1994, 265, 943.
