Fluorescence Amplification in Self-Assembled Organic Nanoparticles

May 21, 2010 - Figure 6. Fluorescence spectra of DDOA NPs 1.0 × 10−5 M with ... with tetracene derivatives,(13) trinitrobenzene,(30) or gold NPs. ...
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J. Phys. Chem. C 2010, 114, 10410–10416

Fluorescence Amplification in Self-Assembled Organic Nanoparticles by Excitation Energy Migration and Transfer Alexandre G. L. Olive, Andre´ Del Guerzo,* Christian Scha¨fer, Colette Belin, Guillaume Raffy, and Carlo Giansante UniVersite´ Bordeaux 1, CNRS, Institut des Sciences Mole´culaires, UMR 5255, 351 crs de la Libe´ration, 33405 Talence ce´dex, France ReceiVed: March 19, 2010; ReVised Manuscript ReceiVed: May 7, 2010

The self-assembly of a low molecular weight organic chromophore occurs upon reprecipitation in water and yields 120 nm wide disk-like nanoparticles (NPs), as shown by fluorescence correlation spectroscopy (FCS) and atomic force microscopy (AFM). The NPs are able to incorporate perylene molecules previously present in water at nanomolar concentrations, thus switching ON and sensitizing their fluorescence. The doped NPs display a very high brightness as a result of their significant fluorescence quantum yield (up to 48%), the cumulated molecular absorbance, and the light-harvesting process. Fluorescence polarization spectroscopy also reveals that the efficiency of the donor-to-acceptor energy transfer process is amplified by a donor-todonor excitation energy migration. 1. Introduction Self-assembly of chemical species by weak noncovalent interactions is a widespread strategy exploited by Nature in its forms and functions1 and is attracting increasing interest in the realization of artificial systems.2 Self-assembly has brought considerable advantages in the bottom-up approach to highly emissive multichromophoric nanostructures for light-harvesting and opto-electronic purposes.3-6 Great attention has recently been devoted to the self-assembly of low molecular weight organic chromophores as an alternative route to obtain nanomaterials with interesting opto-electronic properties.7 Herein we exploit the self-assembly of a low molecular weight organic chromophore, an n-acene derivative, to form a new kind of bright nanoparticles (NPs) combining both high absorption and emission quantum yields. We have thus explored their capacity to act as light-harvesting matrixes and fluorescence amplifiers of emissive n-acenes or PAH that are doped into the NPs. Prominent work on the amplification of trace-induced signal modification has been performed in conjugated polymers using the concept of multichromophore fluorescence quenching sustained by exciton hopping.8 In these conjugated polymers, one analyte species is able to quench the emission of several chromophores by constituting a local energy trap toward which the excitons can rapidely hop. Nanostructured self-assemblies have rarely been envisaged as amplifying media for traces, although the same mechanisms could be exploited (as illustrated in Scheme 1).9 Lately, it has been shown in organogels that excitation energy transfer processes can occur.10 Among these, we have shown that the emission of small amounts of suitable tetracene derivatives11 hosted into 2,3-didecyloxyanthracene (DDOA) organogels, a network of nanofibers trapping an organic solvent,12 can be amplified by excitation energy transfer.13 In DDOA, as well as in other organogels, this phenomenom is efficiently achieved only when the guest is specifically designed to match the molecular structure of the host in order * To whom correspondence should be addressed. Fax: +33 5 40 00 61 58. E-mail: [email protected].

to form a blend.10-13 Otherwise, very large proportions of energy acceptor are needed.14 The highly emissive character of doped or pristine DDOA organogels was proposed tentatively to be linked to the absence of self-quenching processes, such as strong dipolar coupling or excimer formation, and to the particular molecular packing of DDOA into triads15 (see Figure SI-1 in the Supporting Information). These self-assembled structures are thus of interest in comparison to assemblies or aggregates of other π-chromophores,10 J-aggregates that display high fluorescence quantum yields,16 or systems exploiting aggregation induced enhanced emission (AIEE).17 Some of the drawbacks of organogels can be overcome by the use of NPs. Indeed, NPs are prepared in aqueous media, thus being potentially of interest in biological or environmental issues such as the detection of water polluting polycyclic aromatic hydrocarbons (PAHs).18 Moreover, we demonstrate that, in contrast to organogels, the DDOA NPs can act as good light-harvesting hosts even for the naturally occurring and nonspecifically designed guest perylene at nanomolar concentrations. Finally, due to their low optical density, 2 orders of magnitude lower than in an organogel, the photophysical study of NP solutions can be achieved by standard fluorescence techniques and serve also as a model to explain energy transfer processes in DDOA organogels. In this paper we report the following aspects: (i) the characterization of new bright self-assembled organic nanoparticles; (ii) the switching ON and amplification of the emission of an otherwise self-quenched perylene in water; and (iii) the elucidation of the mechanism of excitation energy transfer. 2. Results and Discussion 2.1. Size and Shape of the NPs. DDOA does not form large crystals and does not dissolve in water, but self-assembles into nanoparticles (NPs) when using a reprecipitation technique.19 The suspension of freshly prepared NPs is stable for a couple of hours, contains a concentration of DDOA typically of 1.0 × 10-5 M, is well-suited for spectroscopic measurements, and

10.1021/jp102512t  2010 American Chemical Society Published on Web 05/21/2010

Fluorescence Amplification in Self-Assembled NPs

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SCHEME 1: Fluorescence Amplification Mechanism in DDOA NPs Including Perylene

Blue arrows: excitation energy migration between DDOA molecules. Yellow arrows: energy transfer from DDOA to perylene. Blue perylenes emit intensely. Left: Self-aggregation in water leads to nonemissive gray perylenes.

emits intensely in the blue spectral region upon excitation at 365 or 385 nm. Fluorescence correlation spectroscopy (FCS) has been used to determine the hydrodynamic diameter (dh) of the resulting fluorescent nano-objects. Figure 1 shows the correlation curve obtained for [DDOA] ) 1.0 × 10-5 M and the least-squares fitting obtained according to a normal diffusion model as expressed by eq 1:20

G(τ) ) G(0)

1 + G(∞) {1 + (τ/τD)}{1 + (ωxy /ωz)2(τ/τD)}2 (1)

where τD is the characteristic residence time, and ωxy and ωz are the lateral and axial radii of the Gaussian detection volume, respectively. These measurements yield values for the diffusion coefficient, D ) 3.5 µm2/s ((20%), according to eq 2:

ωxy2 D) 4τD

(2)

and for the nanoparticle concentration, [NP] ) 1.6 × 10-11 M ((20%), according to eq 3:

G(0) )

1 π ωxy2ωz[NP] 3/2

(3)

Thus each NP is constituted in average of 6.3 × 105 DDOA molecules and has an absorption coefficient of 4.4 × 108 M-1 cm-1.21 The diffusion coefficient of the investigated NPs is related to their hydrodynamic diameter dh and the StokesEinstein model for a spherical particle yields dh ) 120 nm. In this case, the particle is considered to move together with a solvent shell at a uniform velocity in a fluid continuum (“sticking” boundary conditions) and hence dh is representative of the largest diameter without consideration of the shape of the nano-object.22 Despite the lack of success in determining a crystal structure of DDOA, we can reasonably propose that the molecular packing in the NPs is similar to the one previously determined for crystals of a family of 2,3-dialkyloxyanthracenes, i.e. a head-to-tail packing of coaxial triads with ∼60° between each anthracene (Figure SI-1, Supporting Information).15 Assuming this packing (0.829 nm3/molecule), 6.3 × 105 DDOA

Figure 1. Fluorescence correlation spectroscopy (FCS) of (filled black circles) DDOA NPs, (filled gray circles) DDOA/perylene (0.01 equiv) NPs, and (empty gray circles) perylene in water, with almost no emission detected. λex ) 385 nm, λem > 405 nm. Solid lines: Fitting according to eq 1.

molecules would yield a spherical NP with a diameter of 100 nm, in agreement with the FCS data. Atomic Force Microscopy (AFM) performed on a dried dispersion of NPs on mica unravels their aspect ratio (Figure 2). AFM has been preferred over TEM, since it affords height measurements and does not require contrasting agents (like metal coating in TEM). Thus, objects displaying heights mostly 99% over the 400-1500 nm range, has been used to measure quantum yields of NPs. Fluorescence correlation spectroscopy and time-resolved fluorescence anisotropy are performed on a Picoquant Microtime 200 inverted confocal microscope, using a PicoHarp 300 multichannel single photon counter and two MPD SPAD’s. The excitation originates from a frequency doubled Ti-Sa laser (Coherent) tuned at 385 nm with picosecond pulses (4-6 ps) at 4.76 MHz repetition rate. The laser beam is injected by 90° reflection on a spectrally flat beam splitter into the microscope objective (100× UPLSAPO, N.A. 1.4). Linearly polarized excitation light has been obtained with a Babinet Soleil compensator. The emission is collected by transmission through the same beam splitter and a 405 nm long pass filter before being focused on a pinhole. Parallel and perpendicular components of the emitted light have been selected by using a polarizing beam splitter and two Glan-Thompson polarizers before the detectors. FCS traces have been analyzed with Symphotime 5.1.2. The polarization G-factor for DDOA has been determined by using a crystal of 2,3-diheptyloxyanthracene displaying the same emission spectrum as DDOA NPs. AFM measurements have been performed with a CP Thermomicroscope Atomic Force Microscope operated in tapping mode. Samples have been prepared by spin-coating a freshly prepared solution of NPs on freshly cleaved mica. Acknowledgment. The authors thank Dr. Martine Cantuel and Dr. Nathan McCleanaghan for setting up the integrating sphere and Damien Jardel for purifying H2-DDOA by HPLC. This work has been financially supported by the ANR (project 06-JCJC-0030), the Re´gion Aquitaine (Ph.D. fellowship of A.O. and equipment), the French Ministry of Education and Research, and the CNRS. Supporting Information Available: Figures SI-1 (images of crystal structures), SI-2 (FCS curves), SI-3 (fluorescence decays), and SI-4 (fluorescence spectrum). This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Cramer, F. Chaos and order; Wiley-VCH: Weinheim, Germany, 1993.

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(2) Lehn, J.-M. Chem. Soc. ReV. 2007, 36, 151. (3) (a) Jonkheijm, P.; van der Schoot, P. P. A. M.; Schenning, A. P. H. J.; Meijer, E. W. Science 2006, 313, 80. (b) Hirschberg, J. H. K. K.; Brunsveld, L.; Ramzi, A.; Vekemans, J. A. J. M.; Sijbesma, R. P.; Meijer, E. W. Nature 2000, 407, 167. (c) Sijbesma, R. P.; Beijer, F. H.; Brunsveld, L.; Folmer, B. J. B.; Hirschberg, J. H. K. K.; Lange, R. F. M.; Lowe, J. K. L.; Meijer, E. W. Science 1997, 278, 1601. (4) (a) Kaiser, T. E.; Stepanenko, V.; Wu¨rthner, F. J. Am. Chem. Soc. 2009, 131, 6719. (b) Kaiser, T. E.; Scheblykin, I. G.; Thomsson, D.; Wu¨rthner, F. J. Phys. Chem. B 2009, 113, 15836. (c) Zhang, X.; Rehm, S.; Safont-Sempere, M. M.; Wu¨rthner, F. Nat. Chem. 2009, 1, 623. (d) Uemura, S.; Sengupta, S.; Wu¨rthner, F. Angew. Chem. 2009, 121, 7965. Angew. Chem., Int. Ed. 2009, 48, 7825. (5) (a) Zabala Ruiz, A.; Li, H.; Calzaferri, G. Angew. Chem., Int. Ed. 2006, 118, 5408. (b) Zabala Ruiz, A.; Li, H.; Calzaferri, G. Angew. Chem., Int. Ed. 2006, 45, 5282. (c) Yunus, S.; Spano, F.; Patrinoiu, G.; Bolognesi, A.; Botta, C.; Bru¨hwiler, D.; Zabala Ruiz, A.; Calzaferri, G. AdV. Funct. Mater. 2006, 16, 2213. (6) (a) Ajayaghosh, A.; Praveen, V. K. Acc. Chem. Res. 2007, 46, 644. (b) Zang, L.; Che, Y.; Moore, J. S. Acc. Chem. Res. 2008, 41, 1596. (c) Moore, J. S. Acc. Chem. Res. 1997, 30, 402. (d) Stupp, S. I. Chem. ReV. 2005, 105, 1023. (7) For a comprehensive review on zero- and one-dimensional nanostructures see: Zhao, Y. S.; Fu, H.; Peng, A.; Ma, Y.; Xiao, D.; Yao, J. AdV. Mater. 2008, 20, 2859. (8) (a) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. ReV. 2007, 107, 1339. (b) Zhao, X. Y.; Jiang, H.; Schanze, K. S. Macromolecules 2008, 41, 3422. (c) Dwight, S. J.; Gaylord, B. S.; Hong, J. W.; Bazan, G. C. J. Am. Chem. Soc. 2004, 126, 16850. (d) Swager, T. M. Acc. Chem. Res. 1998, 31, 201. (9) Del Guerzo, A.; Pozzo, J.-L. In Molecular Gels; Terech, P., Weiss, R. G., Eds.; Kluwer: Dordrecht, The Netherlands, 2005; p 813. (10) (a) Ajayaghosh, A.; Praveen, V. K.; Vijayakumar, C.; George, S. J. Angew. Chem., Int. Ed. 2007, 46, 6260. (b) Herz, L. M.; Daniel, C.; Silva, C.; Hoeben, F. J. M.; Schenning, A. P. H. J.; Meijer, E. W.; Friend, R. H.; Phillips, R. T. Phys. ReV. B 2003, 68, 045203. (11) Desvergne, J.-P.; Olive, A. G. L.; Sangeetha, N. M.; Reichwagen, J.; Hopf, H.; Del Guerzo, A. Pure Appl. Chem. 2006, 78, 2333. (12) Desvergne, J.-P.; Del Guerzo, A.; Bouas-Laurent, H.; Belin, C.; Reichwagen, J.; Hopf, H. Pure Appl. Chem. 2006, 78, 707. (13) Del Guerzo, A.; Olive, A. G. L.; Reichwagen, J.; Hopf, H.; Desvergne, J.-P. J. Am. Chem. Soc. 2005, 127, 17984. (14) Ajayaghosh, A.; George, S. J.; Praveen, V. K. Angew. Chem., Int. Ed. 2003, 42, 332. (15) Olive, A. G. L.; Raffy, G.; Alouchi, H.; Le´ger, J.-M.; Del Guerzo, A.; Desvergne, J.-P. Langmuir 2009, 25, 8606. (16) (a) Kobayashi, T. J-aggregates; World Scientific: Singapore, 1996. (b) Mo¨bius, D. AdV. Mater. 1995, 7, 437. (17) (a) An, B.-K.; Gihm, S. M.; Chung, J. W.; Park, C. R.; Kwon, S. K.; Park, S. Y. J. Am. Chem. Soc. 2009, 131, 3950. (b) An, B. K.; Kwon, S. K.; Park, S. Y. Angew. Chem., Int. Ed. 2007, 46, 1978. (c) An, B.-K.; Lee, D. S.; Lee, J. S.; Park, Y. S.; Hong, H. S.; Park, S. Y. J. Am. Chem. Soc. 2004, 126, 10232. (d) An, B.-K.; Kwon, S. K.; Jung, S.-D.; Park, S. Y. J. Am. Chem. Soc. 2002, 124, 14410. (18) (a) Lope´z de Alda-Villaiza`n, M. Handbook of Water Analysis; Nollet, L. M. L., Ed.; CRC Press: Boca Raton, FL, 2000. (b) Futoma, D. J.; Smith, S. R. PAHs in Water Systems; CRC Press: Boca Raton, FL, 1981. (19) Kasai, H.; Nalwa, H. S.; Oikawa, H.; Okada, S.; Matsuda, H.; Minami, N.; Kakuta, A.; Ono, K.; Mukoh, A.; Nakanishi, H. Jpn. J. Appl. Phys. 1992, 31, L1132.

Olive et al. (20) (a) Hess, S. T.; Huang, S.; Heikal, A. A.; Webb, W. W. Biochemistry 2002, 41, 697. (b) Topics in Fluorescence Spectroscopy 1; Lakowicz, J. R., Ed.; Plenum Press: New York, 1991; p 337. (21) For DDOA NPs, at 365 nm ε ) 7.0 × 103 cm-1 M-1 ( 10%, extrapolated by comparison with DDOA absorption in THF solution at 1.0 × 10-5 M. (22) Macchioni, A.; Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D. Chem. Soc. ReV. 2008, 37, 479. (23) Bloess, A.; Durand, Y.; Matsushita, M.; Verbeck, R.; Groenen, E. J. J.; Schmidt, J. J. Phys. Chem. A 2001, 105, 3016. (24) Exciton coherent domains can also contribute to the line narrowing. See ref 16a. (25) Crosby, G. A.; Demas, J. N. J. Phys. Chem. 1971, 75, 991. (26) (a) Pålsson, L.-O.; Monkman, A. P. AdV. Mater. 2002, 14, 757. (b) Porre`s, L.; Holland, A.; Pålsson, L.-O.; Monkman, A. P.; Kemp, C.; Beeby, J. J. Fluoresc. 2006, 16, 267. (27) Perylene has been previously dispersed in water using less than 10 µL of perylene solution in THF. The THF is allowed to evaporate by slight heating. (28) At 1 nM perylene, I447/I390 is higher than three times the standard deviation of I447/I390 of pristine DDOA NP emission, thus defining the analytical detection limit. (29) Montalti, M.; Credi, A.; Prodi, L.; Gandolfi, M. T. Handbook of Photochemistry, 3rd ed.; CRC Press: Boca Raton, FL, 2006. (30) Giansante, C.; Olive, A. G. L.; Scha¨fer, C.; Raffy, G.; Del Guerzo, A. Anal. Bioanal. Chem. 2010, 396, 125. (31) Sangeetha, N. M.; Bhat, S.; Raffy, G.; Belin, C.; Loppinet-Serani, A.; Aymonier, C.; Terech, P.; Maitra, U.; Desvergne, J.-P.; Del Guerzo, A. Chem. Mater. 2009, 21, 3424. (32) (a) Kelley, R. F.; Lee, S. J.; Wilson, T. M.; Nakamura, Y.; Tiede, D. M.; Suka, A.; Hupp, J. T.; Wasielewski, M. R. J. Am. Chem. Soc. 2008, 130, 13. (b) Hajjaj, F.; Yoon, Z. S.; Yoon, M. C.; Park, J.; Sakate, A.; Kim, D. H.; Kobuke, Y. J. Am. Chem. Soc. 2006, 128, 4612. (c) Hwang, I.-W.; Park, M.; Ahn, T. K.; Yoon, Z. S.; Ko, D. M.; Kim, D.; Ito, F.; Ishibashi, Y.; Khan, S. R.; Nagasawa, Y.; Miyasaka, H.; Ikeda, C.; Takahashi, R.; Ogawa, K.; Satake, A.; Kobuke, Y. Chem.sEur. J. 2005, 11, 3753. (33) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Kluwer Academic/Plenum Publishers: New York, 1999. (34) Guo, M.; Varnavski, O.; Narayanan, A.; Mongin, O.; Majoral, J.P.; Blanchard-Desce, M.; Goodson, T., III J. Phys. Chem. A 2009, 113, 4763. (35) (a) Berberan-Santos, M. N.; Canceill, J.; Gratton, E.; Jullien, L.; Lehn, J.-M.; So, P.; Sutin, J.; Valeur, B. J. Phys. Chem. 1996, 100, 15. (b) Berberan-Santos, M. N.; Choppinet, P.; Fedorov, A.; Jullien, L.; Valeur, B. J. Am. Chem. Soc. 1999, 121, 2526. (36) Yeow, E. K. L.; Ghiggino, K. L.; Reek, J. N. H.; Crossley, M. J.; Bosman, A. W.; Schenning, A. P. H. J.; Meijer, E. W. J. Phys. Chem. B 2000, 104, 2596. (37) (a) Lunt, R. R.; Giebink, N. C.; Belak, A. A.; Benzinger, J. B.; Forrest, S. R. J. Appl. Phys. 2009, 105, 053711. (b) Lunt, R. R.; Benzinger, J. B.; Forrest, S. R. AdV. Mater. 200922, 1233. (38) Dexter mechanism could also lead to next-neighbor energy transfer, but is highly improbable for longer distance energy transfer. (39) Reichwagen, J.; Hopf, H.; Del Guerzo, A.; Belin, C.; Desvergne, J.-P.; Bouas-Laurent, H. Org. Lett. 2005, 7, 971. (40) Reichwagen, J.; Hopf, H.; Desvergne, J.-P.; Del Guerzo, A.; BouasLaurent, H. Synthesis 2005, 20, 3505. (41) Desvergne, J.-P.; Brotin, T.; Meerschaut, D.; Clavier, G.; Placin, F.; Pozzo, J.-L.; Bouas-Laurent, H. New J. Chem. 2004, 28, 234.

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