Browne, Wesley R.

Feringa, Bernard

Herek, Jennifer L.

Huijser, Annemarie

Sharma, Divya

Zhang, Xiaoyan

English

We report transient absorption spectroscopic studies on the hybrid material composed of porphyrin molecules covalently attached to graphene for investigating the mechanism underlying the reported fluorescence quenching of porphyrin in the hybrid. Excited state dynamics of pure graphene suspension and porphyrin have also been studied as reference samples. A fast excited state decay was observed in the hybrid

Proceedings - University of Groningen

   University of GroningenProbing the origin of fluorescence quenching of a graphene-porphyrin hybrid materialSharma, Divya; Zhang, Xiaoyan; Browne, Wesley R.; Herek, Jennifer L.; Huijser, Annemarie;Feringa, BernardPublished in:Proceedings of the XVIIIth International Conference on Ultrafast PhenomenaIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2013Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Sharma, D., Zhang, X., Browne, W. R., Herek, J. L., Huijser, A., & Feringa, B. (2013). Probing the origin offluorescence quenching of a graphene-porphyrin hybrid material. In M. Chergui, S. Cundiff, A. Taylor, R. D.Vivie-Riedle, & K. Yamanouchi (Eds.), Proceedings of the XVIIIth International Conference on UltrafastPhenomena (41 ed., Vol. 41, pp. 04027-p.1-04027-p.3). University of Groningen, Stratingh Institute forChemistry.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 03-06-2022Probing the origin of fluorescence quenching of agraphene-porphyrin hybrid materialDivya Sharma1,a, Xiaoyan Zhang2, Ben L. Feringa2, Wesley R. Browne2, Jennifer L. Herek1, andAnnemarie Huijser11 Optical Sciences group, MESA+ Institute for Nanotechnology, University of Twente, PO Box 217,7500AE Enschede, The Netherlands2 Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747AG Groningen, TheNetherlandsAbstract. We report transient absorption spectroscopic studies on the hybrid materialcomposed of porphyrin molecules covalently attached to graphene for investigating themechanism underlying the reported fluorescence quenching of porphyrin in the hybrid[1]. Excited state dynamics of pure graphene suspension and porphyrin have also beenstudied as reference samples. A fast excited state decay was observed in the hybrid.1 IntroductionGraphene, a two-dimensional single atomic layer of carbon atoms, has been a topic of intense scientificresearch due to its unusual electronic band structure which leads to interesting physical phenomena,e.g., anomalous quantum hall effect [2], spin-resolved quantum interference [3] and bipolar supercur-rent [4]. In addition, graphene-based hybrid nanomaterials, which combine the unique optical, electri-cal, magnetic and chemical properties of each component have the potential applications in solar cells,sensors and catalysis. Such a hybrid material combining graphene with porphyrin, namely graphene-TPP (tetraphenylporphyrin), has been recently synthesized by cycloaddition reactions [1]. Further,fluorescence spectroscopic studies [1] on graphene-TPP and free TPP-CHO (5-(4-Formylphenyl)-10,15,20-triphenylporphyrin) in dimethylformamide (DMF) (containing similar concentration of por-phyrin) have shown that while TPP-CHO shows strong fluorescence (λpeak : 650 nm and 710 nm),fluorescence of porphyrin is quenched significantly in graphene-TPP. The reduced fluorescence life-time (< 500ps) of the graphene-TPP as compared to that of free TPP-CHO (∼ 10ns) further confirmsthe fast quenching of the porphyrin singlet excited state in the hybrid material. In addition, the fluores-cence quantum yield is reduced from 4% in TPP-CHO to 0.3% for the graphene-TPP hybrid. This hasbeen attributed to either an energy or electron transfer process from the covalently attached porphyrinmolecules to graphene. However, an ultrafast time-resolved spectroscopic study which can resolve themode of interaction and the excited state dynamics of graphene and porphyrin in the hybrid materialis still lacking. It is to be noted that such transient studies can also provide insight into the nature ofthe photoproduct resulting from the S 1 state quenching. To this end, we have conducted femtosecondtransient pump-probe spectroscopy studies on the graphene-TPP hybrid.2 Experimental detailsA 420 nm pump beam (corresponding to the blue side excitation of the Soret band of porphyrin cen-tered at 419 nm, S 0 to S 2 state) is obtained by frequency doubling the nearinfrared output (800-900a e-mail: d.sharma@utwente.nl      This  is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.     EPJ Web of ConferencesDOI: 10.1051/C© Owned by the authors, published by EDP Sciences, 2013,epjconf 201/04027 (2013)4134104027Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20134104027EPJ Web of ConferencesFig. 1. (a) Absorption spectra of TPP-CHO (dash-dotted line), graphene (dashed line) and graphene-TPP (solidline) in DMF, (b) Fluorescence spectra of TPP-CHO (solid line) and graphene-TPP (dashed line).Fig. 2. Transient absorption spectra as a function of time delays for (a) porphyrin (b) graphene and (c) graphene-porphyrin hybrid in DMFnm) obtained from the Noncollinear Optical Parametric Amplifier (NOPA) in a BBO crystal. TheNOPA was pumped by the second harmonic (387 nm) of the fundamental 775 nm, 150 fs pulsesfrom a commercial 1 kHz regeneratively amplified mode-locked Ti:Sapphire laser system (CPA-2001,Clark-MXR Inc.). A white light continuum (covering the spectral range from 465 nm to 685 nm), gen-erated by focusing the fundamental in a 2 mm Sapphire crystal, is used as the probe. The polarizationof pump and probe beams are parallel. The experimental time resolution is ∼ 300 f s.3 Results and DiscussionFemtosecond pump-probe time-resolved absorption spectroscopic studies on the graphene-TPP hybridin DMF were performed with a pump excitation at 420 nm. Excited state dynamics of free TPP-CHOand pure graphene suspension in DMF were also studied, as reference samples.Figure 1 (a) shows the steady-state absorption spectra of graphene-TPP hybrid, free TPP-CHO andgraphene in DMF. Figure 1(b) shows the fluorescence spectra of the hybrid and free TPP-CHO in DMF.Figure 2(a-c) displays the transient absorption spectra of free TPP-CHO, graphene and the hybrid asa function of pump-probe delay times. For free TPP-CHO (Fig. 2a) ground state bleaching (S 0 to S 1transition) is clearly observed as a dip in the transient absorption spectra at 515 nm and additional dipsat 550 nm,590 nm and 646 nm can be assigned to a combination of ground state bleaching (GSB),excited state absorption (ESA) and stimulated emission (centered at 650 nm). The transient spectra ofthe hybrid (Fig. 2c) shows an ESA at early delays (< 30ps) which was observed to decay rapidly. Thedips at 520 nm and 560 nm clearly indicate the signature of the porphyrin in the hybrid. On the otherhand, pure graphene suspension shows a broad ESA which decays gradually over time.04027-p.2XVIIIth International Conference on Ultrafast PhenomenaFig. 3. Kinetic traces as a function of wavelength for (a) porphyrin (b) graphene and (c) graphene -porphyrinhybrid in DMF.Figure 3(a-c) presents the temporal evolution of the differential absorption signals of TPP-CHOgraphene and the hybrid. In TPP-CHO, the kinetic trace (Fig. 3(a)) at the blue wavelength (530 nm)exhibits a positive absorption immediately following the photoexcitation which can be assigned toESA from the S 1 state. A subsequent initial fast relaxation followed by a slower decrease is observed.On the other hand, the kinetics at the red wavelength (655 nm) shows a negative absorption indicatingthe evolution of the stimulated emission band. The ingrowth of this band can be attributed to theinternal conversion from the S 2 to the S 1 state occurring on the picosecond timescale. The kinetictrace of graphene (Fig. 3(b)) at 560 nm shows that the signal exhibits a sharp decrease within the 1ps timescale following photoexcitation. This initial drop can be attributed to the photogeneration ofcarriers by the pump pulse thereby resulting in increased transmissivity of the probe. This is followedby a sharp positive rise which exhibits an initial fast relaxation over a few ps time scales. This can beattributed to the carrier-carrier intraband scattering [5] which equilibrates the photogenerated carriersamong themselves and with the intrinsic charge carriers. The signal then shows a long lived negativetransient signal which does not decay till 700 ps. The graphene-TPP hybrid shows a similar rapid riseof ESA followed by a fast decay.Exponential decay fits to the singlet excited state decay of porphyrin in the hybrid reveal a doubleexponential decay with an initial ultrafast decay of ∼ 7ps, followed by a slower decay of ∼ 0.2ns. Theultrafast timescale can be attributed to the rapid quenching of the singlet excited state of porphyrin.Pure graphene suspension shows only a longer single exponential decay (∼ 0.2ns). To note, the ac-curate determination of this longer timescale (0.2 ns) is out of reach of the 0.8 ns scan range of thepresent experiment.Experiments are currently underway to increase the signal-to-noise ratio to investigate the forma-tion of porphyrin radical cation species (> 600nm). We are also exploring the possibility of increasingthe loading of porphyrin.References1. X. Zhang, L. Hou, A. Cnossen, A. C. Coleman, O. Ivashenko, P. Rudolf, B. J. van Wees, W. R.Browne and B. L. Feringa, Chem. Eur. J. 17, (2011) 8957.2. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V.Dubonos and A. A. Firsov, Nature 438, (2005) 197.3. M. B. Lundeberg and J. A. Folk, Nat. Phys. 5, (2009) 894.4. H. B. Heersche, P. J. Herrero, J. B. Oostinga, L. M. K. Vandersypen and A. F. Morpurgo, Nature446, (2007) 56.5. J. M. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana and M.G. Spencer, Appl. Phys. Lett.92, (2008) 042116.04027-p.3

Probing the origin of fluorescence quenching of a graphene-porphyrin hybrid material

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Probing the origin of fluorescence quenching of a graphene-porphyrin hybrid material

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