Polymer matrix dependence of conformational dynamics within a π-stacked perylenediimide dimer and trimer revealed by single molecule fluorescence spectroscopy

Yoo, Hyejin,Bahng, Hee Won,Wasielewski, Michael R.,Kim, Dongho The Royal Society of Chemistry 2012 Physical chemistry chemical physics Vol.14 No.6

<P>The conformation of embedded molecule in a polymer matrix is sensitive to the local nano-environment that the molecule experiences. Particularly, single molecule spectroscopic methods have been utilized to visualize each molecular conformation in local sites of the polymer matrix by monitoring rotational diffusion and fluctuating fluorescence of the molecule. Here, we have performed single molecule spectroscopic experiments on a π-stacked perylenediimide (PDI) dimer and trimer, in which enhanced π–π interaction in π-stacked PDIs makes the fluorescence lifetime longer, embedded in two different polymers, namely poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) (PBMA), to reveal the conformational change depending on the polymer matrix. The fluorescence lifetimes of π-stacked PDIs are influenced by polymer surroundings because their molecular conformations are dependent on their interactions with the local environment in the polymer matrix. Furthermore, from an in-depth analysis of autocorrelation functions of fluorescence intensity trajectories, we could assign that the first autocorrelation value (lag 1) is larger as the intensity trace becomes more fluctuating. Thus, we expect that π-stacked PDIs, a model system for the formation of PDI excimer-like states, can be utilized to probe the surrounding nano-environment by monitoring the conformational change in real time.</P> <P>Graphic Abstract</P><P>Fluorescence lifetime distributions of π-stacked perylenediimide are different in the PMMA and PBMA polymer matrices due to the conformational change depending on the free volume of two polymers. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cp22377e'> </P>

Thermodynamic efficiency limit of excitonic solar cells

Giebink, Noel C.,Wiederrecht, Gary P.,Wasielewski, Michael R.,Forrest, Stephen R. American Physical Society 2011 Physical review. B, Condensed matter and materials Vol.83 No.19

Excimer Formation Dynamics of Intramolecular π-Stacked Perylenediimides Probed by Single-Molecule Fluorescence Spectroscopy

Yoo, Hyejin,Yang, Jaesung,Yousef, Andrew,Wasielewski, Michael R.,Kim, Dongho American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.11

<P>π-Stacked perylenediimides (PDIs) have strong electronic communication between the individual molecules and show great promise as organic electronic materials for applications in field effect transistors, photovoltaics, and liquid crystal displays. To gain further insight into the relationship between conformational behaviors and electronic structures of π-stacked PDIs, we have investigated changes in the excimer-like state of cofacial PDI oligomers that result from π-stacking in real time by monitoring the single-molecule fluorescence intensity and lifetime trajectories in a PMMA polymer matrix. The fluorescence intensity and lifetime of π-stacked perylenediimides are sensitive to the degree of π-orbital interactions among PDI units, which is strongly associated with molecular conformations in the polymer matrix. Furthermore, our results can be applied to probe the conformational motions of biomolecules such as proteins.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-11/ja910724x/production/images/medium/ja-2009-10724x_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja910724x'>ACS Electronic Supporting Info</A></P>

Ideal diode equation for organic heterojunctions. II. The role of polaron pair recombination

Giebink, N. C.,Lassiter, B. E.,Wiederrecht, G. P.,Wasielewski, M. R.,Forrest, S. R. American Physical Society 2010 Physical review. B, Condensed matter and materials Vol.82 No.15

Role of Organic Counterion in Lead- and Tin-Based Two-Dimensional Semiconducting Iodide Perovskites and Application in Planar Solar Cells

Mao, Lingling,Tsai, Hsinhan,Nie, Wanyi,Ma, Lin,Im, Jino,Stoumpos, Constantinos C.,Malliakas, Christos D.,Hao, Feng,Wasielewski, Michael R.,Mohite, Aditya D.,Kanatzidis, Mercouri G. American Chemical Society 2016 Chemistry of materials Vol.28 No.21

<P>Hybrid halide perovskites are emerging semiconducting materials, with a diverse set of remarkable optoelectronic properties. Besides the widely studied three-dimensional (3D) perovskites, two-dimensional (2D) perovskites show significant potential as photovoltaic (PV) active layers while exhibiting high moisture resistance. Here, we report two series of new 2D halide perovskite solid solutions: (HA)Pb1-xSnxI4 and (BZA)(2)Pb1-xSnxI4 (x = 1, 0.75, 0.5, 0.25, 0), where HA stands for the organic spacer histammonium and BZA stands for benzylammonium cations. These compounds are assembled by corner-sharing octahedral [MI6](4-) units stabilizing single-layered, anionic, inorganic perovskite sheets with organic cations filled in between. The optical band gaps are heavily affected by the M-I-M perovksite angles with the band gap steadily decreasing when the angle approaches 180 degrees, ranging from 2.18 eV for (BZA)(2)PbI4 to 2.05 eV for (HA)PbI4. We find an anomalous trend in electronic band gap in the mixed compositions (HA)Pb1-xSnxI4 and (BZA)(2)Pb1-xSnxI4. When Sn substitutes for Pb to form a solid solution, the band gap further decreases to 1.67 eV for (HA)SnI4. The minimum band gap is at x = 0.75 at 1.74 eV. For BZA, the irregular trend is more intense, as all the intermediate compounds (BZA)(2)Pb(1-x)SnxI(4) (x = 0.75, 0.5, 0.25) have even slightly lower band gaps than (BZA)(2)SnI4 (1.89 eV). DFT calculations confirm the pure Pb and Sn compounds are direct band gap semiconductors. Relatively shorter photoluminescence (PL) lifetime in (BZA)2PbI4 than (HA)PbI4 is observed, suggesting faster recombination rates of the carriers. Solution deposited thin films of (HA)PbI4 and (BZA)2PbI4 show drastically different orientations with (HA)PbI4 displaying a perpendicular rather than parallel growth orientation with respect to the substrate, which is more favorable for PV devices. The higher potential in PV applications of the HA system is indicated by device performance, as the champion air stable planar device with the structure ITO/PEDOT:PSS/2D-perovskite/PCBM/Al of (HA)PbI4 achieves a preliminary power conversion efficiency (PCE) of 1.13%, featuring an open-circuit voltage (VOC) of 0.91 V.</P>

Large Porphyrin Squares from the Self-Assembly of meso-Triazole-Appended L-Shaped meso–meso-Linked Zn^II–Triporphyrins: Synthesis and Efficient Energy Transfer

Maeda, Chihiro,Kim, Pyosang,Cho, Sung,Park, Jong Kang,Lim, Jong Min,Kim, Dongho,Vura-Weis, Josh,Wasielewski, Michael R.,Shinokubo, Hiroshi,Osuka, Atsuhiro WILEY-VCH Verlag 2010 Chemistry Vol.16 No.17

<P>meso-Triazolyl-appended Zn<SUP>II</SUP>–porphyrins were readily prepared by Cu<SUP>I</SUP>-catalyzed 1,3-dipolar cycloaddition of benzyl azide to meso-ethynylated Zn<SUP>II</SUP>–porphyrin (click chemistry). In noncoordinating CHCl<SUB>3</SUB> solvent, spontaneous assembly occurred to form tetrameric array (3)<SUB>2</SUB> from meso–meso-linked diporphyrins 3, and dodecameric porphyrin squares (4)<SUB>4</SUB> and (5)<SUB>4</SUB> from the L-shaped meso–meso-linked triporphyrins 4 and 5. The structures of these assemblies were examined by <SUP>1</SUP>H NMR spectra, absorption spectra, and their gel permeation chromatography (GPC) retention time. Furthermore, the structures of the dodecameric porphyrin squares (4)<SUB>4</SUB> and (5)<SUB>4</SUB> were probed by small- and wide-angle X-ray scattering (SAXS/WAXS) measurements in solution using a synchrotron source. Excitation-energy migration processes in these assemblies were also investigated in detail by using both steady-state and time-resolved spectroscopic methods, which revealed efficient excited-energy transfer (EET) between the meso–meso-linked Zn<SUP>II</SUP>–porphyrin units that occurred with time constants of 1.5 ps<SUP>−1</SUP> for (3)<SUB>2</SUB> and 8.8 ps<SUP>−1</SUP> for (5)<SUB>4</SUB>.</P> <B>Graphic Abstract</B> <P>Getting it together: In a noncoordinating solvent, spontaneous assembly occurs to form a tetrameric array from meso–meso-linked diporphyrins, and a dodecameric porphyrin square from L-shaped meso–meso-linked triporphyrins (see graphic). Efficient excited-energy transfer (EET) between the meso–meso-linked Zn<SUP>II</SUP>–porphyrin units was revealed. <img src='wiley_img_2010/09476539-2010-16-17-CHEM200903195-content.gif' alt='wiley_img_2010/09476539-2010-16-17-CHEM200903195-content'> </P>

Excitonic Coupling in Linear and Trefoil Trimer Perylenediimide Molecules Probed by Single-Molecule Spectroscopy

Yoo, Hyejin,Furumaki, Shu,Yang, Jaesung,Lee, Ji-Eun,Chung, Heejae,Oba, Tatsuya,Kobayashi, Hiroyuki,Rybtchinski, Boris,Wilson, Thea M.,Wasielewski, Michael R.,Vacha, Martin,Kim, Dongho American Chemical Society 2012 The Journal of physical chemistry B Vol.116 No.42

<P>Perylenediimide (PDI) molecules are promising building blocks for photophysical studies of electronic interactions within multichromophore arrays. Such PDI arrays are important materials for fabrication of molecular nanodevices such as organic light-emitting diodes, organic semiconductors, and biosensors because of their high photostability, chemical and physical inertness, electron affinity, and high tinctorial strength over the entire visible spectrum. In this work, PDIs have been organized into linear (<B>L3</B>) and trefoil (<B>T3</B>) trimer molecules and investigated by single-molecule fluorescence microscopy to probe the relationship between molecular structures and interchromophoric electronic interactions. We found a broad distribution of coupling strengths in both <B>L3</B> and <B>T3</B> and hence strong/weak coupling between PDI units by monitoring spectral peak shifts in single-molecule fluorescence spectra upon sequential photobleaching of each constituent chromophore. In addition, we used a wide-field defocused imaging technique to resolve heterogeneities in molecular structures of <B>L3</B> and <B>T3</B> embedded in a PMMA polymer matrix. A systematic comparison between the two sets of experimental results allowed us to infer the correlation between intermolecular interactions and molecular structures. Our results show control of the PDI intermolecular interactions using suitable multichromophoric structures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2012/jpcbfk.2012.116.issue-42/jp307394x/production/images/medium/jp-2012-07394x_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp307394x'>ACS Electronic Supporting Info</A></P>

Controlling Switching in Bistable [2]Catenanes by Combining Donor–Acceptor and Radical–Radical Interactions

Zhu, Zhixue,Fahrenbach, Albert C.,Li, Hao,Barnes, Jonathan C.,Liu, Zhichang,Dyar, Scott M.,Zhang, Huacheng,Lei, Juying,Carmieli, Raanan,Sarjeant, Amy A.,Stern, Charlotte L.,Wasielewski, Michael R.,Sto American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.28

<P>Two redox-active bistable [2]catenanes composed of macrocyclic polyethers of different sizes incorporating both electron-rich 1,5-dioxynaphthalene (DNP) and electron-deficient 4,4′-bipyridinium (BIPY<SUP>2+</SUP>) units, interlocked mechanically with the tetracationic cyclophane cyclobis(paraquat-<I>p</I>-phenylene) (CBPQT<SUP>4+</SUP>), were obtained by donor–acceptor template-directed syntheses in a threading-followed-by-cyclization protocol employing Cu(I)-catalyzed azide–alkyne 1,3-dipolar cycloadditions in the final mechanical-bond forming steps. These bistable [2]catenanes exemplify a design strategy for achieving redox-active switching between two translational isomers, which are driven (i) by donor–acceptor interactions between the CBPQT<SUP>4+</SUP> ring and DNP, or (ii) radical–radical interactions between CBPQT<SUP>2(•+)</SUP> and BIPY<SUP>•+</SUP>, respectively. The switching processes, as well as the nature of the donor–acceptor interactions in the ground states and the radical–radical interactions in the reduced states, were investigated by single-crystal X-ray crystallography, dynamic <SUP>1</SUP>H NMR spectroscopy, cyclic voltammetry, UV/vis spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy. The crystal structure of one of the [2]catenanes in its trisradical tricationic redox state provides direct evidence for the radical–radical interactions which drive the switching processes for these types of mechanically interlocked molecules (MIMs). Variable-temperature <SUP>1</SUP>H NMR spectroscopy reveals a degenerate rotational motion of the BIPY<SUP>2+</SUP> units in the CBPQT<SUP>4+</SUP> ring for both of the two [2]catenanes, that is governed by a free energy barrier of 14.4 kcal mol<SUP>–1</SUP> for the larger catenane and 17.0 kcal mol<SUP>–1</SUP> for the smaller one. Cyclic voltammetry provides evidence for the reversibility of the switching processes which occurs following a three-electron reduction of the three BIPY<SUP>2+</SUP> units to their radical cationic forms. UV/vis spectroscopy confirms that the processes driving the switching are (i) of the donor–acceptor type, by the observation of a 530 nm charge-transfer band in the ground state, and (ii) of the radical–radical ilk in the switched state as indicated by an intense visible absorption (ca. 530 nm) and near-infrared (ca. 1100 nm) bands. EPR spectroscopic data reveal that, in the switched state, the interacting BIPY<SUP>•+</SUP> radical cations are in a fast exchange regime. In general, the findings lay the foundations for future investigations where this radical–radical recognition motif is harnessed in bistable redox-active MIMs in order to achieve close to homogeneous populations of co-conformations in both the ground and switched states.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-28/ja3037355/production/images/medium/ja-2012-037355_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3037355'>ACS Electronic Supporting Info</A></P>

Tetrathiafulvalene Hetero Radical Cation Dimerization in a Redox-Active [2]Catenane

Wang, Cheng,Dyar, Scott M.,Cao, Dennis,Fahrenbach, Albert C.,Horwitz, Noah,Colvin, Michael T.,Carmieli, Raanan,Stern, Charlotte L.,Dey, Sanjeev K.,Wasielewski, Michael R.,Stoddart, J. Fraser American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.46

<P>The electronic properties of tetrathiafulvalene (TTF) can be tuned by attaching electron-donating or electron-withdrawing substituents. An electron-rich macrocyclic polyether containing two TTF units of different constitutions, namely 4,4′-bis(hydroxymethyl)tetrathiafulvalene (OTTFO) and 4,4′-bisthiotetrathiafulvalene (STTFS), has been synthesized. On two-electron oxidation, a hetero radical dimer is formed between OTTFO<SUP>•+</SUP> and STTFS<SUP>•+</SUP>. The redox behavior of the macrocyclic polyether has been investigated by electrochemical techniques and UV–vis and electron paramagnetic resonance (EPR) spectroscopies. The [2]catenane in which the macrocyclic polyether is mechanically interlocked with the cyclobis(paraquat-<I>p</I>-phenylene) (CBPQT<SUP>4+</SUP>) ring has also been prepared using template-directed protocols. In the case of the [2]catenane, the formation of the TTF hetero radical dimer is prevented sterically by the CBPQT<SUP>4+</SUP> ring. After a one-electron oxidation, a 70:30 ratio of OTTFO<SUP>•+</SUP> to STTFS<SUP>•+</SUP> is present at equilibrium, and, as a result, two translational isomers of the [2]catenane associated with these electronically different isomeric states transpire. EPR titration spectroscopy and simulations reveal that the radical states of the two constitutionally different TTF units in the [2]catenane still experience long-range electronic intramolecular coupling interactions, despite the presence of the CBPQT<SUP>4+</SUP> ring, when one or both of them are oxidized to the radical cationic state. These findings in the case of both the free macrocyclic polyether and the [2]catenane have led to a deeper fundamental understanding of the mechanism of radical cation dimer formation between constitutionally different TTF units.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-46/ja307577t/production/images/medium/ja-2012-07577t_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja307577t'>ACS Electronic Supporting Info</A></P>