Distance-Dependent Triplet Energy Transfer ... - ACS Publications

Subscriber access provided by UNIV LAVAL

Letter

Distance Dependent Triplet Energy Transfer between CdSe Nanocrystals and Surface Bound Anthracene Xin Li, Zhiyuan Huang, Ramsha Zavala, and Ming L. Tang J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b00761 • Publication Date (Web): 10 May 2016 Downloaded from http://pubs.acs.org on May 10, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Distance Dependent Triplet Energy Transfer between CdSe Nanocrystals and Surface Bound Anthracene Xin Li, Zhiyuan Huang, Ramsha Zavala, Ming Lee Tang* Department of Chemistry, University of California, Riverside, Riverside CA 92521. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 17

ABSTRACT. Here we investigate triplet energy transfer (TET) across variable-length aromatic oligo-p-phenylene and aliphatic bridges in a covalently linked CdSe nanocrystal (NC)-bridgeanthracene

hybrid

system.

Photon

upconversion

measurements

in

saturated

9,10-

diphenylanthracene hexane solutions under air-free conditions at room temperature provided the steady-state rate of TET (ket) across this interface. For flexible transmitters, ket is similar for different lengths of aliphatic bridges, suggesting the ligands bending backwards. For the rigid phenylene spacer, triplet sensitization of anthracene transmitter molecules by CdSe NCs shows a strong distance dependence, with a Dexter damping coefficient of 0.43±0.07 Å-1. The anthracene transmitter bound closest to the NC surface gave the highest QY of 14.3% for the conversion of green

to

violet

light,

the

current

record

for

a

hybrid

platform.

TOC GRAPHICS


2

Page 3 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


KEYWORDS Upconversion • Dexter transfer • Triplet-triplet annihilation Among existing upconversion methods, sensitized triplet-triplet annihilation (TTA) based photon upconversion is the only one with demonstrated potential for harvesting incoherent photons from the sun.1-2 In TTA based upconversion, the sensitizer harvests the low energy photons, which are subsequently transferred to the emitting species capable of TTA. During TTA, two molecules in their triplet excited state combine to form a molecule in its singlet excited state and a molecule in its ground state, thus upconverting light. Recently, our group and others showed that inorganic nanocrystals (NCs) are viable alternatives3-5 to the organometallic compounds conventionally6-8 used as sensitizers. Even though the high density of states above the band gap in NCs seems may result in the reabsorption of upconverted light, the best upconversion quantum yield achieved in this hybrid upconversion system, 14.3%, is comparable to that achieved in molecule-based upconversion. The role of NCs as sensitizers makes strategic use of their intrinsic optical properties, such as a large absorption coefficient, excellent photostability and low cost, advantageous for photon upconversion.9-10 As the long insulating ligands on the as-synthesized NC impede efficient energy transfer, installing a transmitter ligand on NC surface is crucial for mediating triplet energy transfer across this interface.4,

11

This

transmitter accelerates triplet energy transfer (TET) to the 9, 10-diphenylanthracene (DPA) emitters by forming an energy cascade, as shown in Fig. 1(a).


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 17

Figure 1 (a) Schematic of the energy transfer in this hybrid photon upconversion platform. The energy diagram depicts the triplet excitonic states of the CdSe NC, the p-phenylene (ph) bridges when n=1 and 2, and the anthracene transmitter. (b) Absorption, fluorescence spectra for 9ACA, CPA, CPPA, CP4A, CP9A ligands and 2.6 nm CdSe NCs. The spectra were taken at room temperature in hexane, the same solvent as the upconversion experiments. The green arrow indicates the 532 nm excitation wavelength.

An understanding of the mechanism of triplet energy transfer from inorganic semiconductor NC donors to the organic acceptors is essential for improving the performance of this hybrid upconversion system. Studies of energy transfer12-13 mainly focus on the kinetics of the energy transfer events and their dependence on reaction driving-force, distance, chemical environment or the linkage between the donor and acceptor.14-19 A traditional approach to explore long-range energy transfer involves the use of covalent donor–bridge–acceptor systems. However, most such studies are focused on charge or Förster energy transfer.14, 20-22 Previous work has shown surprisingly efficient energy transfer from triplets generated in acenes to lead chalcogenide nanocrystals following Dexter-type mechanism.23-24 However, while ligand exchange was necessary for the high efficiencies, it has been shown to alter NC photoluminescence quantum yield and intrinsic decay rate.25 Therefore, we are interested in


4

Page 5 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


elucidating this TET process quantitatively in a model system where the acceptor molecule is covalently linked to the NCs in a well-defined manner. This work investigates the effect of donor-acceptor distance on TET across rigid aromatic and flexible aliphatic spacers in a covalently linked CdSe NC-bridge-anthracene system. The rate of TET (ket) is extracted from the upconversion quantum yield (QY) that was obtained under steady state cw illumination. For the rigid spacer, the rate constant for energy transfer is exponentially dependent on the length of the oligo-p-phenylene bridge, following the Dexter energy transfer mechanism. The empirical damping coefficient, β, is fitted to be 0.43±0.07 Å -1. Surprisingly, different lengths of flexible aliphatic bridges have no effect on the rate of energy transfer. This interesting phenomenon may be the first experimental evidence for flexible ligands not being fully extended on a NC surface and bending over instead. These results not only further the mechanistic understanding of TET in hybrid NC-organic systems, but also facilitate the rational design and selection of the appropriate transmitters in hybrid optoelectronic systems. As shown in Fig. 1(a), a series of different anthracene ligands are linked to 2.6 nm CdSe NCs through variable-length oligo-p-phenylene or aliphatic bridges with a carboxylic acid group. The energy diagram in Fig. 1(a) illustrates that the TET from NCs to anthracene is exergonic by roughly 0.55 eV.26 As the emitter species, we choose diphenylanthracene (DPA), which is commonly used in organic−organic upconversion schemes due to its long-lived, low-lying triplet state and relatively high fluorescence quantum yields (90%) 27. Synthetic details for these novel ligands can be found in the supporting information.28-32 Their absorption and emission are shown in Fig. 1(b). The upconversion QY was optimized by varying the concentration of anthracene ligands in the ligand exchange solution. (see Fig. S1). The upconversion QY is defined as follows:


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 17

(1) The average number of bound anthracene ligands per CdSe NC (n) was determined using UVVis electronic absorption spectroscopy (see SI/ Fig. S2). Since n is small (Table S1), it is impossible to characterize n using NMR. The values of n (n = 0.78-3, Table S1) obtained are consistent with previously reported studies for the binding of carboxylic acid ligands to octadecylphosphonic acid (ODPA) capped CdSe NCs.

33-34

While we realize the distribution of

bound ligands on NCs should follow Poissonian statistics, we do not have enough information to fully model this. The highest upconversion QY obtained for 9ACA, CPA and CPPA are 14.3%, 3.9% and 0.4% respectively (Fig. 2), and the average values are listed in Table S1. A similar result was also observed when the same experiments were performed on a different batch of 2.6 nm CdSe NCs (see Fig. S3). We relate the rate of energy transfer (ket) to the efficiency of TET (ΦET). ΦET can be calculated from the measured upconversion QY, ΦUC, based on the following equation,

ΦUC = Φ ET Φ TTA Φ A

(2)

because our experiments are conducted in the linear regime with regards to excitation power density and nanocrystal concentration, where TTA is the main decay pathway of the triplet excited states in DPA.35-36 ΦUC, ΦET, ΦTTA, ΦA are the quantum yields of upconversion, energy transfer, triplet-triplet annihilation and acceptor fluorescence respectively (see Fig. 1a). In this work, ΦA, the fluorescence QY of DPA, is 0.9 based on previous studies.27, 37 As for ΦTTA, standard spin statistics predict that the fraction of triplet-triplet encounters that lead to a singlet is


6

Page 7 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


11.1%. However, the TTA process is usually more efficient since quintet states are not energetically accessible.38-42 Here, we use ΦTTA =0.52 based on a report by Monguzzi et. al. for DPA.40, 43 It is assumed that DPA excited triplet state is consumed by triplet-triplet annihilation, and other monomolecular decay processes such as intersystem crossing or bimolecular processeses such as oxygen or impurity quenching are not involved (since samples are air-free). Based on the maximum upconversion QY measured, ΦET is calculated to be 30.5%, 7.8% and 0.85% for 9ACA, CPA and CPPA respectively. The rate of energy transfer, ket, is correlated with the efficiency of energy transfer (ΦET) by equation 3, which is similar to that previously used by Ding et. al to calculate the yield of hole transfer from CdSe/CdS core/shell NCs to ferrocene.44

Φ ET =

nk et kr + k nr + nket

(3)

In equation 3, n is the average number of bound anthracene ligands on the surface of NCs, ket is the rate of energy transfer from one CdSe NC to each bound ligand, kr and knr are the intrinsic radiative and non-radiative decay rates of CdSe NCs without anthracene ligands. It is assumed that the intrinsic decay rates are unchanged in the presence of the carboxylic acid functionalized ligands, an assumption verified experimentally.33, 45 Here, TET introduces a new decay channel on top of the original intrinsic decay pathways, analogous to the perturbation introduced by charge transfer. From equation (3), it is clear that ket can be calculated once ΦET and the NC’s intrinsic decay rates are known. For our CdSe NCs, the PL decays can be fitted to multiexponentials, with lifetimes of 37 ps, 286 ps, 54 ns and 182 ns respectively (Fig. S4). So far, two groups have reported rates of TTET that differ by two orders


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 17

of magnitude. If we choose the fast decay component, 286 ps for example, ket is calculated to be about 2.0×109 s-1, similar to what Castellano et. al measure with transient aborption spectroscopy.5 On the other hand, if we select the components on the nanoscecond timescale, 54 ns or 184 ns, our calculated value, around 1.0×107 s-1, agrees with the rate reported by Bardeen et. al.45 Therefore, more work must be done to understand the photophysics underpining energy transfer between nanocrystals and molecular triplet states. Note that the intrinsic decay rates of the NC end up as a prefactor on the calculated ket and do not affect the value obtained for β, the Dexter damping coefficient, which is given by the slope of the plot in Fig. 2 (see the SI for details).

Figure 2. The rate of triplet energy transfer (ket, red squares) and maximum upconversion QY (blue triangles) are shown versus the phenylene bridge length of covalently bound transmitter anthracene ligands on CdSe nanocrystals. The logarithmic relation of ket is consistent with Dexter energy transfer and a damping coefficient, β , of 0.43±0.07 Å-1.

There is a logarithmic relationship between the donor-acceptor distance and the rate of energy transfer (ket), consistent with Dexter energy transfer as the dominant mechanism (Fig. 2). The distance dependence of ket can be described by equation 4, where d is the length of the energy barrier and β is an empirical damping coefficient that describes the extent of coupling through the barrier material.


8

Page 9 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


k et = k 0 exp( − β d )

(4)

The experimentally determined β for the CdSe-(phenylene)n-anthracene system is found to be 0.43 ± 0.07 Å-1. If we include the original, unfunctionalized ODPA-capped CdSe NCs, where the upconversion QY is 0.026%, then β is 0.42 ± 0.02 Å-1 (Fig. S5). The same experimental result can be reproduced on another batch of 2.6 nm CdSe NCs for a β value of 0.61 ± 0.04 Å-1 (Fig. S3(c)). The value of β depends on the energy offset between the donor and acceptor (0.55 eV here), as well as the height and length of the tunneling barrier between the two species. In the case of the CdSe-(phenyl)n-anthracene system, the length of the phenyl bridge is systematically elongated by increasing the number of phenylene units from 0 to 2 going from 9ACA to CPA to CPPA. However, the barrier height is not constant, because the first excited triplet states of benzene and bisphenylene are 3.67 and 2.85 eV respectively,15,

46-47

as drawn in Fig. 1(a).

Nonetheless, the β value obtained here is comparable to that measured in organic donor-acceptor systems. In the case of hole transfer from a perylene-3,4:9,10-bis(dicarboximide) donor to a phenothianzine acceptor, the rate constant had a strong distance dependence with a β value of 0.46 Å−1.48-49 However, as Dexter energy transfer can be regarded as the correlated transfer or two charges50, β is expected to be twice that of charge transfer for the same barrier.51-54 In cases where only triplet energy transfer occurs, the Ru(bpy)32+(bpy= 2,2`-bipyridine)-phenylene bridge-Os(bpy)32+ system gave a β value of 0.50 Å−1.47, 55 The tunneling barrier created by the phenylene bridge between the CdSe NC and anthracene impedes efficient energy transfer, leading to a strong distance dependence. In our case, the carboxylic acid group may also contribute to the tunneling barrier. In terms of NC-molecule systems, a value of β = 0.24 Å−1 and 0.85 Å−1 was reported for hole transfer from CdSe NC donors to ferrocene acceptors across CdS and alkyl barriers respectively.44, 56 To our knowledge, this is the first report quantifying the


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 17

Dexter damping coefficient characterizing energy transfer between nanocrystals and molecular triplet states. A lower β value indicates stronger coupling, or a lower tunneling barrier57, and the values measured here compare well considering the dielectric constants and energetic barriers introduced by the spacer. Another way of quantifying the efficiency of energy transfer, ΦET, is by relating any change in NC PL to the triplet sensitization of anthracene. For clarification, we labeled it as ΦET(NC) . ΦET(NC) follows the same trend as the ΦET obtained from upconversion QY, but only to a limited extent (see Fig. S6) because the low average number of bound ligands and strong distance dependence leads to a weak effect on NC PL for ligands with a long bridge. The flexible aliphatic transmitter ligands, CP4A and CP9A, give an unexpectedly high upconversion QY that shows no distance dependence. For both transmitters, the maximal upconversion QY is about 3.0% (see Table S1), which is similar to the optimized upconversion QY of the rigid CPA ligand. Given the fact that the fully extended spacer lengths for CPA, CP4A and CP9A are drastically different (6.2 Å, 10.9 Å and 15.5 Å respectively), the consistency in upconversion QY is quite surprising. Note that the unifying motif between these three transmitters is the single rigid phenyl group separating the anthracene moiety from the NC surface. A similar trend was also observed when we performed the same experiment on a different batch of 2.6 nm CdSe NCs (see Fig. S3). Therefore we infer that the lack of distance dependence in the upconversion QY for the aliphatic ligands as strong evidence that these flexible molecules bend over on the surface of CdSe NC,58 either through thermal fluctuations or a curved ligand binding geometry.


10

Page 11 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In conclusion, TET from CdSe NCs to bound anthracene ligands shows a strong distance dependence. The highest upconversion QY of 14.3% was attained for the transmitter ligand covalently bound closest to the NC surface. The rate of triplet energy transfer showed a logarithmic dependence on the distance between the CdSe donor and anthracene acceptor for rigid phenylene bridges, with an experimentally determined Dexter damping coefficient of 0.43±0.07 Å -1. This work confirms that NC donors and molecular acceptors must be in close proximity for efficient correlated electron exchange necessary for high upconversion QYs. Work is underway in this laboratory to design ligands with a lower energy barrier and better chemical affinity for the NC surface. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website: Descriptions of anthracene ligand and CdSe nanocrystal synthesis, upconversion experiment details, measurement of average bound ligands, time-resolved photoluminescence data for CdSe NC (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel: +01 (951) 827-5964. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The authors acknowledge financial support from the U.S. Army W911NF-14-1-0260 for instrumentation, and the National Science Foundation CHE-1351663.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 17

REFERENCES 1. Mahato, P.; Monguzzi, A.; Yanai, N.; Yamada, T.; Kimizuka, N. Fast and Long-range Triplet Exciton Diffusion in Metal-Organic Frameworks for Photon Upconversion at Ultralow Excitation Power. Nat. Mater. 2015, 14, 924-930. 2. Monguzzi, A.; Borisov, S. M.; Pedrini, J.; Klimant, I.; Salvalaggio, M.; Biagini, P.; Melchiorre, F.; Lelii, C.; Meinardi, F. Efficient Broadband Triplet–Triplet Annihilation-Assisted Photon Upconversion at Subsolar Irradiance in Fully Organic Systems. Adv. Funct. Mater. 2015, 25, 5617-5624. 3. Wu, M.; Congreve, D. N.; Wilson, M. W. B.; Jean, J.; Geva, N.; Welborn, M.; Van Voorhis, T.; Bulović, V.; Bawendi, M. G.; Baldo, M. A. Solid-state Infrared-to-visible Upconversion Sensitized by Colloidal Nanocrystals. Nat. Photonics 2015, 10, 31-34. 4. Huang, Z.; Li, X.; Mahboub, M.; Hanson, K. M.; Nichols, V. M.; Le, H.; Tang, M. L.; Bardeen, C. J. Hybrid Molecule–Nanocrystal Photon Upconversion Across the Visible and NearInfrared. Nano Lett. 2015, 15, 5552-5557. 5. Mongin, C.; Garakyaraghi, S.; Razgoniaeva, N.; Zamkov, M.; Castellano, F. N. Direct Observation of Triplet Energy Transfer from Semiconductor Nanocrystals. Science 2016, 351, 369-372. 6. 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. 7. Monguzzi, A.; Tubino, R.; Meinardi, F. Multicomponent Polymeric Film for Red to Green Low Power Sensitized Up-Conversion. J. Phys. Chem. A 2009, 113, 1171-1174. 8. Sugunan, S. K.; Tripathy, U.; Brunet, S. M. K.; Paige, M. F.; Steer, R. P. Mechanisms of Low-Power Noncoherent Photon Upconversion in Metalloporphyrin−Organic Blue Emitter Systems in Solution. J. Phys. Chem. A 2009, 113, 8548-8556. 9. Alivisatos, A. P. Perspectives on the Physical Chemistry of Semiconductor Nanocrystals. J. Phys. Chem. 1996, 100, 13226-13239. 10. Talapin, D. V.; Lee, J.-S.; Kovalenko, M. V.; Shevchenko, E. V. Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chem. Rev. 2010, 110, 389-458. 11. Huang, Z.; Simpson, D. E.; Mahboub, M.; Li, X.; Tang, M. L. Ligand Enhanced Upconversion of Near-infrared Photons with Nanocrystal Light Absorbers. Chem. Sci. 2016. 12. Debreczeny, M. P.; Wasielewski, M. R.; Shinoda, S.; Osuka, A. Singlet−Singlet Energy Transfer Mechanisms in Covalently-Linked Fucoxanthin− and Zeaxanthin−Pyropheophorbide Molecules. J. Am. Chem. Soc. 1997, 119, 6407-6414. 13. Vura-Weis, J.; Abdelwahed, S. H.; Shukla, R.; Rathore, R.; Ratner, M. A.; Wasielewski, M. R. Crossover from Single-Step Tunneling to Multistep Hopping for Molecular Triplet Energy Transfer. Science 2010, 328, 1547-1550. 14. Adams, D. M.; Brus, L.; Chidsey, C. E.; Creager, S.; Creutz, C.; Kagan, C. R.; Kamat, P. V.; Lieberman, M.; Lindsay, S.; Marcus, R. A. Charge Transfer on the Nanoscale: Current Status. J. Phys. Chem. B 2003, 107, 6668-6697. 15. Wenger, O. S. Photoinduced Electron and Energy Transfer in Phenylene Oligomers. Chem. Soc. Rev. 2011, 40, 3538-3550. 16. Hyo Jae, Y.; Shapiro, N. D.; Kyeng Min, P.; Thuo, M. M.; Siowling, S.; Whitesides, G. M. The Rate of Charge Tunneling Through Self-assembled Monolayers is Insensitive to Many Functional Group Substitutions. Angew. Chem. Int. Ed. 2012, 51, 4658-61.


12

Page 13 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17. Faure, S.; Stern, C.; Guilard, R.; Harvey, P. D. Role of the Spacer in the Singlet−Singlet Energy Transfer Mechanism (Förster vs Dexter) in Cofacial Bisporphyrins. J. Am. Chem. Soc. 2004, 126, 1253-1261. 18. Osuka, A.; Tanabe, N.; Kawabata, S.; Yamazaki, I.; Nishimura, Y. Synthesis and Intramolecular Electron- and Energy-Transfer Reactions of Polyyne- or Polyene-Bridged Diporphyrins. J. Org. Chem. 1995, 60, 7177-7185. 19. Zhu, H.; Yang, Y.; Hyeon-Deuk, K.; Califano, M.; Song, N.; Wang, Y.; Zhang, W.; Prezhdo, O. V.; Lian, T. Auger-Assisted Electron Transfer from Photoexcited Semiconductor Quantum Dots. Nano Lett. 2014, 14, 1263-1269. 20. Clapp, A. R.; Medintz, I. L.; Mauro, J. M.; Fisher, B. R.; Bawendi, M. G.; Mattoussi, H. Fluorescence Resonance Energy Transfer between Quantum Dot Donors and Dye-Labeled Protein Acceptors. J. Am. Chem. Soc. 2004, 126, 301-310. 21. Beane, G.; Boldt, K.; Kirkwood, N.; Mulvaney, P. Energy Transfer between Quantum Dots and Conjugated Dye Molecules. J. Phys. Chem. C 2014, 118, 18079-18086. 22. Hoffman, J. B.; Choi, H.; Kamat, P. V. Size-Dependent Energy Transfer Pathways in CdSe Quantum Dot–Squaraine Light-Harvesting Assemblies: Förster versus Dexter. J. Phys. Chem. C 2014, 118, 18453-18461. 23. Thompson, N. J.; Wilson, M. W.; Congreve, D. N.; Brown, P. R.; Scherer, J. M.; Bischof, T. S.; Wu, M.; Geva, N.; Welborn, M.; Van Voorhis, T. Energy Harvesting of Non-emissive Triplet Excitons in Tetracene by Emissive PbS Nanocrystals. Nature materials 2014, 13, 1039-1043. 24. Tabachnyk, M.; Ehrler, B.; Gélinas, S.; Böhm, M. L.; Walker, B. J.; Musselman, K. P.; Greenham, N. C.; Friend, R. H.; Rao, A. Resonant Energy Transfer of Triplet Excitons from Pentacene to PbSe Nanocrystals. Nature materials 2014, 13, 1033-1038. 25. Anderson, N. C.; Hendricks, M. P.; Choi, J. J.; Owen, J. S. Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metalcarboxylate Displacement and Binding. J. Am. Chem. Soc. 2013, 135, 18536-18548. 26. Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of Photochemistry. Marcel Dekker: New York: 1993. 27. Morris, J. V.; Mahaney, M. A.; Huber, J. R. Fluorescence Quantum Yield Determinations. 9,10-Diphenylanthracene as a Reference Standard in Different Solvents. J. Phys. Chem. 1976, 80, 969-974. 28. Yao, L.; Pan, Y.; Tang, X.; Bai, Q.; Shen, F.; Li, F.; Lu, P.; Yang, B.; Ma, Y. Tailoring Excited-State Properties and Electroluminescence Performance of Donor–Acceptor Molecules through Tuning the Energy Level of the Charge-Transfer State. J. Phys. Chem. C 2015, 119, 17800-17808. 29. Shi, D.; Ren, Y.; Jiang, H.; Lu, J.; Cheng, X. A New Three-dimensional Metal-organic Framework Constructed from 9,10-Anthracene Dibenzoate and Cd(ii) as a Highly Active Heterogeneous Catalyst for Oxidation of Alkylbenzenes. Dalton Trans. 2013, 42, 484-491. 30. Travis, B. R.; Narayan, R. S.; Borhan, B. Osmium Tetroxide-Promoted Catalytic Oxidative Cleavage of Olefins: An Organometallic Ozonolysis. J. Am. Chem. Soc. 2002, 124, 3824-3825. 31. Ishiyama, T.; Murata, M.; Miyaura, N. Palladium(0)-Catalyzed Cross-Coupling Reaction of Alkoxydiboron with Haloarenes: A Direct Procedure for Arylboronic Esters. J. Org. Chem. 1995, 60, 7508-7510. 32. Ogawa, T.; Yanai, N.; Monguzzi, A.; Kimizuka, N. Highly Efficient Photon Upconversion in Self-Assembled Light-Harvesting Molecular Systems. Scientific Reports 2015, 5, 10882.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 17

33. Li, X.; Nichols, V. M.; Zhou, D.; Lim, C.; Pau, G. S. H.; Bardeen, C. J.; Tang, M. L. Observation of Multiple, Identical Binding Sites in the Exchange of Carboxylic Acid Ligands with CdS Nanocrystals. Nano Lett. 2014, 14, 3382-3387. 34. Gomes, R.; Hassinen, A.; Szczygiel, A.; Zhao, Q.; Vantomme, A.; Martins, J. C.; Hens, Z. Binding of Phosphonic Acids to CdSe Quantum Dots: A Solution NMR Study. J. Phys. Chem. Lett. 2011, 2, 145-152. 35. Monguzzi, A.; Mezyk, J.; Scotognella, F.; Tubino, R.; Meinardi, F. Upconversion-induced Fluorescence in Multicomponent Systems: Steady-state Excitation Power Threshold. Phys. Rev. B 2008, 78, 195112. 36. Schmidt, T. W.; Castellano, F. N. Photochemical Upconversion: the Primacy of Kinetics. J. Phys. Chem. Lett. 2014, 5, 4062-4072. 37. Martinho, J.; Maçanita, A.; Berberan‐Santos, M. The Effect of Radiative Transport on Fluorescence Emission. The Journal of chemical physics 1989, 90 (1), 53-59. 38. Singh-Rachford, T. N.; Castellano, F. N. Photon Upconversion Based on Sensitized Triplet– triplet Annihilation. Coord. Chem. Rev. 2010, 254, 2560-2573. 39. Cheng, Y. Y.; Khoury, T.; Clady, R. G.; Tayebjee, M. J.; Ekins-Daukes, N.; Crossley, M. J.; Schmidt, T. W. On the Efficiency Limit of Triplet–triplet Annihilation for Photochemical Upconversion. Phys. Chem. Chem. Phys. 2010, 12, 66-71. 40. Monguzzi, A.; Tubino, R.; Hoseinkhani, S.; Campione, M.; Meinardi, F. Low power, Noncoherent Sensitized Photon Up-conversion: Modelling and Perspectives. Phys. Chem. Chem. Phys. 2012, 14, 4322-4332. 41. Khnayzer, R. S.; Blumhoff, J.; Harrington, J. A.; Haefele, A.; Deng, F.; Castellano, F. N. Upconversion-powered Photoelectrochemistry. Chem. Commun. 2012, 48, 209-211. 42. Cheng, Y. Y.; Fückel, B.; Khoury, T.; Clady, R. G. C. R.; Tayebjee, M. J. Y.; EkinsDaukes, 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. 43. Sripathy, K.; MacQueen, R. W.; Peterson, J. R.; Cheng, Y. Y.; Dvořák, M.; McCamey, D. R.; Treat, N. D.; Stingelin, N.; Schmidt, T. W. Highly Efficient Photochemical Upconversion in a Quasi-Solid Organogel. J. Mater. Chem. C 2015, 3, 616-622. 44. Ding, T. X.; Olshansky, J. H.; Leone, S. R.; Alivisatos, A. P. Efficiency of Hole Transfer from Photoexcited Quantum Dots to Covalently Linked Molecular Species. J. Am. Chem. Soc. 2015, 137, 2021-2029. 45. Piland, G. B.; Huang, Z.; Lee Tang, M.; Bardeen, C. J. Dynamics of Energy Transfer from CdSe Nanocrystals to Triplet States of Anthracene Ligand Molecules. J. Phys. Chem. C 2016, 120, 5883-5889. 46. Doering, J. P. Electronic Energy Levels of Benzene below 7 eV. J. Chem. Phy. 1977, 67, 4065-4070. 47. Lafolet, F.; Welter, S.; Popović, Z.; De Cola, L. Iridium Complexes Containing p-Phenylene Units. The Influence of the Conjugation on the Excited State Properties. J. Mater. Chem. 2005, 15, 2820-2828. 48. Weiss, E. A.; Ahrens, M. J.; Sinks, L. E.; Gusev, A. V.; Ratner, M. A.; Wasielewski, M. R. Making a Molecular Wire: Charge and Spin Transport through para-Phenylene Oligomers. J. Am. Chem. Soc. 2004, 126, 5577-5584.


14

Page 15 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


49. Weiss, E. A.; Tauber, M. J.; Kelley, R. F.; Ahrens, M. J.; Ratner, M. A.; Wasielewski, M. R. Conformationally Gated Switching between Superexchange and Hopping within Oligo-pphenylene-Based Molecular Wires. J. Am. Chem. Soc. 2005, 127, 11842-11850. 50. Turro, N. J. Modern Molecular Photochemistry. University science books: 1991. 51. Closs, G. L.; Johnson, M. D.; Miller, J. R.; Piotrowiak, P. A Connection between Intramolecular Long-range Electron, Hole, and Triplet Energy Transfers. J. Am. Chem. Soc. 1989, 111, 3751-3753. 52. Kroon, J.; Oliver, A. M.; Paddon-Row, M. N.; Verhoeven, J. W. Observation of a Remarkable Dependence of the Rate of Singlet-singlet Energy Transfer on the Configuration of the Hydrocarbon Bridge in Bichromophoric Systems. J. Am. Chem. Soc. 1990, 112, 4868-4873. 53. Scholes, G. D. Long-range Resonance Energy Transfer in Molecular Systems. Annu. Rev. Phys. Chem. 2003, 54, 57-87. 54. Scholes, G. D.; Ghiggino, K. P. Electronic Interactions and Interchromophore Excitation Transfer. J. Phys. Chem. 1994, 98, 4580-4590. 55. Welter, S.; Salluce, N.; Belser, P.; Groeneveld, M.; De Cola, L. Photoinduced Electronic Energy Transfer in Modular, Conjugated, Dinuclear Ru(II)/Os(II) Complexes. Coord. Chem. Rev. 2005, 249, 1360-1371. 56. Zhu, H.; Song, N.; Lian, T. Controlling Charge Separation and Recombination Rates in CdSe/ZnS Type I Core−Shell Quantum Dots by Shell Thicknesses. J. Am. Chem. Soc. 2010, 132, 15038-15045. 57. Köhler, A.; Bässler, H. What Controls Triplet Rxciton Transfer in Organic Semiconductors? J. Mater. Chem. 2011, 21, 4003-4011. 58. Wind, M.; Wiesler, U.-M.; Saalwächter, K.; Müllen, K.; Spiess, H. W. Shape-Persistent Polyphenylene Dendrimers: Restricted Molecular Dynamics from Advanced Solid-State Nuclear Magnetic Resonance Techniques. Adv. Mater. 2001, 13, 752-756.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

Page 16 of 17

Page 17 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. The rate of triplet energy transfer (ket, red squares) and maximum upconversion QY (blue triangles) are shown versus the phenylene bridge length of covalently bound transmitter anthracene ligands on CdSe nanocrystals. The logarithmic relation of ket is consistent with Dexter energy transfer and a damping coefficient, β, of 0.43±0.07Å-1. 144x101mm (150 x 150 DPI)


Distance-Dependent Triplet Energy Transfer ... - ACS Publications

Recommend Documents