Co-reporter:Alec Pickett, Abhisek Mohapatra, Amrit Laudari, Soma Khanra, Thulasi Ram, Satish Patil, Suchismita Guha
Organic Electronics 2017 Volume 45(Volume 45) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.orgel.2017.03.001
•Nanopatterned ZnO films pave the way for efficient non-fullerene hybrid near IR photodetectors.•Two near IR diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers with variations in backbone conformations are synthesized.•The DPP copolymer with the thienothiophene linker shows a high photoresponsivity.•Capacitance-voltage measurements from hybrid Schottky barrier interfaces shed light into device parameters.Hybrid organic-inorganic photodiode interfaces have gained significant interest due to their unique physical properties such as mechanical flexibility and high photosensitivity. Two diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers with different backbone conformations are characterized in an inverted non-fullerene photodiode architecture using ZnO nano-patterned films as the electron transport layer. The DPP copolymer with a thienothiophene unit (PBDT-TTDPP) is more planar and rigid compared to the DPP system with a thiophene unit connecting the donor and acceptor moieties within the monomer (PBDT-TDPP). The hybrid interfaces were optimized by using poly(3-hexylthiophene) (P3HT) as the p-type layer for monitoring the critical thickness and morphology of the ZnO layer. The maximum photoresponsivity from a P3HT:ZnO photodiode was found to be 56 mA/W. The photoresponsivity of PBDT-TTDPP:ZnO photodiodes were found to be more than two orders of magnitude higher than PBDT-TDPP:ZnO photodiodes, which is attributed to an enhanced transport of carriers due to the planar backbone conformation of the PBDT-TTDPP copolymer. Capacitance-voltage measurements from hybrid Schottky barrier interfaces further shed light into the nature of photocarriers and device parameters. First-principles time-dependent density-functional theoretical calculations yield a higher absorptivity for the PBDT-TTDPP dimer compared to PBDT-TDPP.Nanopatterned ZnO and diketopyrrolopyrrole (DPP) donor-acceptor copolymer based planar heterojunctions provide a viable route for near-infrared photodetector applications. The rigid backbone of the DPP copolymer with a thienothiophene unit enhances charge transport properties.Download high-res image (184KB)Download full-size image
Co-reporter:Soma Khanra;Kartik Ghosh;Fabio F. Ferreira;Wendel A. Alves;Francesco Punzo;Ping Yu
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 4) pp:3084-3093
Publication Date(Web):2017/01/25
DOI:10.1039/C6CP07879F
Self-assembled L,L-diphenylalanine (FF) peptide micro/nanotubes represent a class of biomimetic materials with a non-centrosymmetric crystal structure and strong piezoelectricity. The peptide nanotubes synthesized by a liquid phase method yield tube lengths in the hundreds of micron range, inner diameters in the few hundred nanometer range, and outer diameters in the 5–15 μm range. Second harmonic generation (SHG) polarimetry from individual self-assembled FF nanotubes is used to obtain the nonlinear (NLO) optical coefficients as a function of the tube diameter and thermal treatment. The ratio of the shear to the longitudinal component (d15/d33) of the NLO coefficient increases with the diameter of the tubes. One of the transverse components of the nonlinear coefficient is found to be negative, and its magnitude with respect to the longitudinal component increases with the tube diameter. Thermal treatment of individual FF tubes has a similar effect upon increasing the diameter of the tubes in SHG polarimetry. Concurrent Raman scattering measurements from individual FF tubes show a distinct change in the low frequency (100 cm−1) region with the diameter of the tubes reflecting subtle effects of water.
Co-reporter:Soma Khanra;Thiago Cipriano;Thomas Lam;Tommi A. White;Eudes E. Fileti;Wendel A. Alves
Advanced Materials Interfaces 2015 Volume 2( Issue 14) pp:
Publication Date(Web):
DOI:10.1002/admi.201500265
Based on self-assembly and mimicking strategies occurring in nature, peptide nanomaterials play a unique role in a new generation of hybrid materials for the electronics of the 21st century. This report describes the functionalization of diphenylalanine (FF)-based micro/nanostructures with blue-emitting conducting polymers of the polyfluorene (PF) family. The FF:PF polymer nanocomposites are synthesized by a liquid-vapor phase method. Electron microscopy images reveal di-octyl-substituted PF (PF8) to bind better to the FF micro/nanotubes in comparison with ethyl-hexyl PF (PF2/6), which influences its optical properties. Molecular dynamics simulations of FF nanotubes with monomeric units of PFs show that PF8 favors greater proximity to the grooves on the surface of the nanotubes due to a higher van der Waals interaction energy compared to PF2/6. The FF:PF nanocomposites are further utilized in light-emitting diodes. Biodegradability tests from FF:PF8 nanocomposite films show more than 80% weight loss in 2 h by enzymatic action compared to PF8 pristine films, which do not degrade. Self-assembly of FF nanostructures with organic semiconductors opens up a new generation of biocompatible and biodegradable materials in organic electronics.
Co-reporter:Thiago Cipriano, Grant Knotts, Amrit Laudari, Roberta C. Bianchi, Wendel A. Alves, and Suchismita Guha
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 23) pp:21408
Publication Date(Web):November 7, 2014
DOI:10.1021/am5064124
Peptide-based nanostructures derived from natural amino acids are superior building blocks for biocompatible devices as they can be used in a bottom-up process without the need for expensive lithography. A dense nanostructured network of l,l-diphenylalanine (FF) was synthesized using the solid–vapor-phase technique. Formation of the nanostructures and structure–phase relationship were investigated by electron microscopy and Raman scattering. Thin films of l,l-diphenylalanine micro/nanostructures (FF-MNSs) were used as the dielectric layer in pentacene-based field-effect transistors (FETs) and metal–insulator–semiconductor diodes both in bottom-gate and in top-gate structures. Bias stress studies show that FF-MNS-based pentacene FETs are more resistant to degradation than pentacene FETs using FF thin film (without any nanostructures) as the dielectric layer when both are subjected to sustained electric fields. Furthermore, it is demonstrated that the FF-MNSs can be functionalized for detection of enzyme–analyte interactions. This work opens up a novel and facile route toward scalable organic electronics using peptide nanostructures as scaffolding and as a platform for biosensing.Keywords: electrochemical impedance spectroscopy; field-effect transistors; pentacene; peptide nanostructures
Co-reporter:Dhanashree Moghe, Gitish K. Dutta, Satish Patil and Suchi Guha
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 9) pp:4291-4298
Publication Date(Web):06 Jan 2014
DOI:10.1039/C3CP54644F
Diketopyrrolopyrrole (DPP) containing copolymers have gained a lot of interest in organic optoelectronics with great potential in organic photovoltaics. In this work, DPP based statistical copolymers, with slightly different bandgap energies and a varying fraction of donor–acceptor ratio are investigated using monochromatic photocurrent spectroscopy and Fourier-transform photocurrent spectroscopy (FTPS). The statistical copolymer with a lower DPP fraction, when blended with a fullerene derivative, shows the signature of an inter charge transfer complex state in photocurrent spectroscopy. Furthermore, the absorption spectrum of the blended sample with a lower DPP fraction is seen to change as a function of an external bias, qualitatively similar to the quantum confined Stark effect, from where we estimate the exciton binding energy. The statistical copolymer with a higher DPP fraction shows no signal of the inter charge transfer states and yields a higher external quantum efficiency in a photovoltaic structure. In order to gain insight into the origin of the observed charge transfer transitions, we present theoretical studies using density-functional theory and time-dependent density-functional theory for the two pristine DPP based statistical monomers.
Co-reporter:Suchismita Guha;Matti Knaapila;Dhanashree Moghe;Zuzana Konôpková;Mika Torkkeli;Martin Fritsch;Ullrich Scherf
Journal of Polymer Science Part B: Polymer Physics 2014 Volume 52( Issue 15) pp:1014-1023
Publication Date(Web):
DOI:10.1002/polb.23520
ABSTRACT
The role of high pressure on a low molecular weight nematic liquid crystalline organic semiconductor, ethyl-hexyl substituted polyfluorene (PF2/6) is investigated using photoluminescence (PL), Raman scattering, and X-ray scattering studies at pressures from 1 to 8 GPa. The PL and the Raman data under pressure are consistent with each other with no abrupt changes in the pressure coefficients of PL or Raman peaks. The PL energies redshift and broaden, consistent with both enhanced intra- and interchain interactions. The Raman peak positions yield pressure coefficients similar to other phenyl based π-conjugated polymers. The broadening of a doublet peak in the 1135 cm−1 region indicates a more planar backbone conformation with increasing pressure. X-ray scattering indicates that the torsion angle between adjacent repeats reduces with increasing pressure and reverts back with decompression. The intermolecular structure is weakly ordered (frozen nematic) and essentially maintained with increasing pressure, in contrast to a high molecular weight PF2/6. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1014–1023
Co-reporter:Ndubuisi B. Ukah;Satyaprasad P. Senanayak;Danish Adil;Grant Knotts;Jimmy Granstrom;K. S. Narayan;Suchi Guha
Journal of Polymer Science Part B: Polymer Physics 2013 Volume 51( Issue 21) pp:1533-1542
Publication Date(Web):
DOI:10.1002/polb.23366
ABSTRACT
Low-operating voltage, high mobility, and stable organic field-effect transistors (OFETs) using polymeric dielectrics such as pristine poly(4-vinyl phenol) (PVP) and poly(methyl methacrylate) (PMMA), dissolved in solvents of high dipole moment, have been achieved. High dipole moment solvents such as propylene carbonate and dimethyl sulfoxide used for dissolving the polymer dielectric enhance the charge carrier mobilities by three orders of magnitude in pentacene OFETs compared with low dipole moment solvents. Fast switching circuits with patterned gate PVP-based pentacene OFETs demonstrated a switching frequency of 75 kHz at input voltages of |5 V|. The frequency response of the OFETs is attributed to a high degree of dipolar-order in dielectric films obtained from high-polarity solvents and the resulting energetically ordered landscape for transport. Remarkably, these pentacene-based OFETs exhibited high stability under bias stress and in air with negligible shifts in the threshold voltage. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1533–1542
Co-reporter:Danish Adil and Suchi Guha
The Journal of Physical Chemistry C 2012 Volume 116(Issue 23) pp:12779-12785
Publication Date(Web):May 22, 2012
DOI:10.1021/jp3031804
The performance of organic field-effect transistors (OFETs) largely depends on the nature of interfaces of dissimilar materials. Metal–semiconductor interfaces, in particular, play a critical role in the charge injection process. This work demonstrates the unique potential of Raman and surface-enhanced Raman scattering (SERS) for the investigation of physical phenomena at the nanoscale in pentacene–metal interfaces in OFETs. A large enhancement in the Raman intensity (SERS) is observed from pentacene films under thermally evaporated Au films. Comparing experiments with density functional theoretical calculations of the Raman spectrum of pentacene indicates the presence of disordered sp2 carbons. Changes in the Raman spectra are further tracked after biasing the devices. Raman maps across the pentacene–Au interface provide a powerful visualization tool for correlating the device performance with structural changes of the molecule.
Co-reporter:Danish Adil, Catherine Kanimozhi, Ndubuisi Ukah, Keshab Paudel, Satish Patil, and Suchi Guha
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 5) pp:1463
Publication Date(Web):March 31, 2011
DOI:10.1021/am200028u
Two donor−acceptor diketopyrrolopyrrole (DPP)-based copolymers (PDPP-BBT and TDPP-BBT) have been synthesized for their application in organic devices such as metal−insulator semiconductor (MIS) diodes and field-effect transistors (FETs). The semiconductor-dielectric interface was characterized by capacitance−voltage and conductance−voltage methods. These measurements yield an interface trap density of 4.2 × 1012 eV−1cm−2 in TDPP-BBT and 3.5 × 1012 eV−1cm−2 in PDPP-BBT at the flat-band voltage. The FETs based on these spincoated DPP copolymers display p-channel behavior with hole mobilities of the order 10−3 cm2/(V s). Light scattering studies from PDPP-BBT FETs show almost no change in the Raman spectrum after the devices are allowed to operate at a gate voltage, indicating that the FETs suffer minimal damage due to the metal−polymer contact or the application of an electric field. As a comparison Raman intensity profile from the channel-Au contact layer in pentacene FETs are presented, which show a distinct change before and after biasing.Keywords: capacitance−voltage characteristics; diketopyrrolopyrrole; donor−acceptor; field-effect transistors; metal−insulator−semiconductor; Raman scattering
Co-reporter:N.B. Ukah, D. Adil, J. Granstrom, R.K. Gupta, K. Ghosh, S. Guha
Organic Electronics 2011 Volume 12(Issue 9) pp:1580-1587
Publication Date(Web):September 2011
DOI:10.1016/j.orgel.2011.06.006
The electrical properties of matrix-assisted pulsed-laser evaporated (MAPLE) 9,9-dioctylfluorene-co-bis-N-N-(4-butylphenyl)-bis-N,N-phenyl 1,4-phenylenediamine (PFB)-based bottom-gate organic field-effect transistors (FETs) and metal–insulator–semiconductor (MIS) diodes with poly (methyl methacrylate) (PMMA) as the dielectric layer have been investigated. The device characteristics were found to improve with an increase in the difference between the solubility parameters of PMMA and solvent. Shifts in flat band voltage of the MIS diodes were found to be due to the difference in the density of trapped holes located at the semiconductor–insulator interface. The threshold voltage of the FETs were correlated with differences in acceptor doping density and flat band voltage shifts of the MIS diodes, thereby demonstrating the role of interface traps in determining the electrical properties of organic devices. Electrical characterization of the FET shows the device to have a hysteresis-free operation in its transfer characteristics, a low threshold voltage of −0.2 V, and a field-effect mobility of 0.2 × 10−4 cm2 V−1 s−1. Interface trap states of the MIS diodes were found to be distributed in energy with their density decreasing non-linearly from approximately 2.8 × 1012 to 1.2 × 1012 eV−1 cm−2 over an energy range of 0.075–0.385 eV above the bulk Fermi level. Non-orthogonality of the semiconductor solvent had no deleterious effects on the underlying PMMA dielectric layer even without any high temperature baking, thus demonstrating that MAPLE is a viable technique for fabricating polymer dielectric-based devices and for improving the semiconductor–insulator interface.Graphical abstractHighlights► New technique (MAPLE) for circumventing inherent solvent selectivity problem. ► PMMA dielectric-based organic FETs and MIS diodes. ► The PMMA dielectric was dissolved in three different solvents. ► The solvents’ solubility parameter is correlated with interface trap density in MIS diodes. ► Qualitative link between flat band voltage in MIS to threshold voltage in FETs.
Co-reporter:Gitish K. Dutta, S. Guha, Satish Patil
Organic Electronics 2010 Volume 11(Issue 1) pp:1-9
Publication Date(Web):January 2010
DOI:10.1016/j.orgel.2009.09.012
Two new donor–acceptor type liquid crystalline semiconductors based on benzothiazole have been synthesized. Their structural, photophysical and electronic properties were investigated using X-ray diffraction, atomic force microscopy, cyclic voltammetry, UV–Vis, photoluminescence, and Raman spectroscopy. The liquid crystalline behaviour of the molecules was thoroughly examined by differential scanning calorimetry (DSC) and optical polarizing microscope. The DSC and thermogravimetric analysis (TGA) show that these materials posses excellent thermal stability and have decomposition temperatures in excess of 300 °C. Beyond 160 °C both molecules show a smectic A liquid crystalline phase that exists till about 240 °C. Field-effect transistors were fabricated by vacuum evaporating the semiconductor layer using standard bottom gate/top contact geometry. The devices exhibit p-channel behaviour with hole mobilities of 10−2 cm2/Vs.
Co-reporter:K. Paudel, H. Knoll, M. Chandrasekhar and S. Guha
The Journal of Physical Chemistry A 2010 Volume 114(Issue 13) pp:4680-4688
Publication Date(Web):March 17, 2010
DOI:10.1021/jp911778r
Polyfluorenes (PFs) represent a unique class of poly-para-phenylene-based blue-emitting polymers with intriguing structure−property relationships. Slight variations in the choice of functionalizing side chains result in dramatic differences in the inter- and intrachain structures in PFs. Dioctyl-substituted PF (PF8) is characterized by different backbone conformations that depend upon the torsion angle between the monomers. We present photoluminescence (PL) and Raman scattering studies of bulk samples and thin films of dioctyl-substituted PF (PF8) under hydrostatic pressure. The bulk sample was further thermally annealed and studied as a function of pressure. The PL energies of the as-is and thermally annealed samples both red shift but at very different rates, and the difference between their pressure coefficients elucidates the role of the backbone torsional angle. This is further corroborated by density functional theoretical calculations of a fluorene oligomer, where the energy gap is calculated as a function of both the torsion angle as well as compression. The Raman peaks harden with increasing pressures; the intraring C−C stretch frequency at 1600 cm−1 has a pressure coefficient of 7.2 cm−1/GPa and exhibits asymmetric line shapes at higher pressures, characteristic of a strong electron−phonon interaction.
Co-reporter:K. Yang, M. Arif, M. Förster, U. Scherf, S. Guha
Synthetic Metals 2009 Volume 159(21–22) pp:2338-2341
Publication Date(Web):November 2009
DOI:10.1016/j.synthmet.2009.07.041
Inclusion of trace quantities of heavy metal atoms (Pd) in a ladder-type polymer (PhLPPP) backbone allows transitions between the singlet and the triplet manifolds. Temperature-dependent photoinduced absorption studies of PhLPPP show the triplet–triplet absorption peak (T1 → TN) at 1.3 eV to blue-shift with increasing temperatures, suggesting a localization of the excitons on smaller chain segments with large exchange splitting energy. Furthermore, solar cells were fabricated using PhLPPP as the donor material; on an average the power conversion efficiencies of PhLPPP-based solar cells were 3–10 times greater compared to the ladder-type polymer with no incorporation of Pd atoms.
Co-reporter:R.K. Gupta, K. Ghosh, P.K. Kahol, J. Yoon, S. Guha
Applied Surface Science 2008 Volume 254(Issue 21) pp:7069-7073
Publication Date(Web):30 August 2008
DOI:10.1016/j.apsusc.2008.05.198
Abstract
Matrix-assisted pulsed laser deposition (PLD) allows a controlled layer-by-layer growth of polymer films. Di-octyl substituted polyfluorene (PF8) and its copolymers were deposited as thin films using matrix-assisted PLD by employing a KrF excimer laser with a fluence of 125 mJ/pulses. The optical and structural properties of these films are compared with spincoated films via Raman spectroscopy, absorption and photoluminescence. The Raman spectra of both PLD and spincoated films are similar indicating that the polymer films deposited via PLD maintain their molecular structure. Both the spincoated and the PLD grown PF8 films that were cast from toluene show the presence of the β phase. Benzothiadiazole substituted PF8 (F8BT) and butyl phenyl-substituted PF8 (PFB) PLD grown films show a slightly broader emission compared to the spincoated films, which is attributed to an enhanced intermolecular interaction in the PLD grown thin films.
Co-reporter:M. Yun, S. Gangopadhyay, M. Bai, H. Taub, M. Arif, S. Guha
Organic Electronics 2007 Volume 8(Issue 5) pp:591-600
Publication Date(Web):October 2007
DOI:10.1016/j.orgel.2007.04.007
Hybrid metal–insulator–semiconductor structures based on ethyl-hexyl substituted polyfluorene (PF2/6) as the active polymer semiconductor were fabricated on a highly doped p-Si substrate with Al2O3 as the insulating oxide layer. We present detailed frequency-dependent capacitance–voltage (C–V) and conductance–voltage characteristics of the semiconductor/insulator interface. PF2/6 undergoes a transition to an ordered crystalline phase upon thermal cycling from its nematic-liquid crystalline phase, confirmed by our atomic force microscope images. Thermal cycling of the PF2/6 films significantly improves the quality of the (PF2/6)/Al2O3 interface, which is identified as a reduced hysteresis in the C–V curve and a decreased interface state density (Dit) from ∼3.9 × 1012 eV−1 cm−2 to ∼3.3 × 1011 eV−1 cm−2 at the flat-band voltage. Interface states give rise to energy levels that are confined to the polymer/insulator interface. A conductance loss peak, observed due to the capture and emission of carriers by the interface states, fits very well with a single time constant model from which the Dit values are inferred.
Co-reporter:Suchi Guha, Kazuo Nakamoto
Coordination Chemistry Reviews 2005 Volume 249(9–10) pp:1111-1132
Publication Date(Web):May 2005
DOI:10.1016/j.ccr.2004.11.017
Endohedral fullerenes belong to a new class of compounds which are technologically and scientifically important owing to their unique structures and optoelectronic properties. This review focuses on theoretical calculations and spectroscopic (electronic, vibrational, and nuclear magnetic resonance (NMR)) studies of endohedral fullerenes thus far published. A theoretical background, with various computational methods used for determining energy-optimized electronic structure and calculation of vibrational spectra, is presented. Further, theoretical and spectroscopic investigations of individual endohedral fullerenes are discussed. Such studies provide structural information about the carbon cage, position of the encapsulated species, and the degree of charge transfer. In particular, 13C NMR spectroscopy is indispensable for the determination of the cage symmetry. In some cases, NMR signals from 45Sc encapsulated species yield information about dynamic behavior inside the cage. Vis–NIR absorption spectra determine the HOMO–LUMO band-gap energy. IR and Raman spectroscopy play an important role in elucidating the nature of interaction between the cage and encapsulated species. Novel vibrations resulting from these interactions appear in the low-frequency region, and the corresponding force constants serve as a measure of the strength of their interaction.
Co-reporter:Soma Khanra, Kartik Ghosh, Fabio F. Ferreira, Wendel A. Alves, Francesco Punzo, Ping Yu and Suchismita Guha
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 4) pp:NaN3093-3093
Publication Date(Web):2017/01/04
DOI:10.1039/C6CP07879F
Self-assembled L,L-diphenylalanine (FF) peptide micro/nanotubes represent a class of biomimetic materials with a non-centrosymmetric crystal structure and strong piezoelectricity. The peptide nanotubes synthesized by a liquid phase method yield tube lengths in the hundreds of micron range, inner diameters in the few hundred nanometer range, and outer diameters in the 5–15 μm range. Second harmonic generation (SHG) polarimetry from individual self-assembled FF nanotubes is used to obtain the nonlinear (NLO) optical coefficients as a function of the tube diameter and thermal treatment. The ratio of the shear to the longitudinal component (d15/d33) of the NLO coefficient increases with the diameter of the tubes. One of the transverse components of the nonlinear coefficient is found to be negative, and its magnitude with respect to the longitudinal component increases with the tube diameter. Thermal treatment of individual FF tubes has a similar effect upon increasing the diameter of the tubes in SHG polarimetry. Concurrent Raman scattering measurements from individual FF tubes show a distinct change in the low frequency (100 cm−1) region with the diameter of the tubes reflecting subtle effects of water.
Co-reporter:Dhanashree Moghe, Gitish K. Dutta, Satish Patil and Suchi Guha
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 9) pp:NaN4298-4298
Publication Date(Web):2014/01/06
DOI:10.1039/C3CP54644F
Diketopyrrolopyrrole (DPP) containing copolymers have gained a lot of interest in organic optoelectronics with great potential in organic photovoltaics. In this work, DPP based statistical copolymers, with slightly different bandgap energies and a varying fraction of donor–acceptor ratio are investigated using monochromatic photocurrent spectroscopy and Fourier-transform photocurrent spectroscopy (FTPS). The statistical copolymer with a lower DPP fraction, when blended with a fullerene derivative, shows the signature of an inter charge transfer complex state in photocurrent spectroscopy. Furthermore, the absorption spectrum of the blended sample with a lower DPP fraction is seen to change as a function of an external bias, qualitatively similar to the quantum confined Stark effect, from where we estimate the exciton binding energy. The statistical copolymer with a higher DPP fraction shows no signal of the inter charge transfer states and yields a higher external quantum efficiency in a photovoltaic structure. In order to gain insight into the origin of the observed charge transfer transitions, we present theoretical studies using density-functional theory and time-dependent density-functional theory for the two pristine DPP based statistical monomers.
![Poly[9,9-bis-(2-ethylhexyl)-9H-fluorene-2,7-diyl]](http://img.cochemist.com/ccimg/188300/188201-16-3.png)
![Poly[9,9-bis-(2-ethylhexyl)-9H-fluorene-2,7-diyl]](http://img.cochemist.com/ccimg/188300/188201-16-3_b.png)
