Synthesis, Characterization, and Photophysical, Electrochemical, Electroluminescent, and Photovoltaic Properties of Yne-Containing CN−PPVs

Abstract

Alkoxy-substituted CN-containing phenylene−vinylene−alt-phenylene−ethynylene hybrid polymers (CN−PPV−PPE), 3a, 3b, and 7a, were obtained from luminophoric dialdehydes 1 by step growth polymerization via Knoevenagel reaction as high molecular-weight materials. Corresponding CN-free polymers 3c and 7b and an ethynylene-free polymer 5 with similar side chains were synthesized for the purpose of comparison. The chemical structures of the polymers were confirmed by IR, 1H and 13C NMR, and elemental analysis. Thermal characterization was conducted by means of thermogravimetric analysis and differential scanning calorimetry. Morphology was investigated by means of optical microscopy and small-angle light scattering. The final morphologies are determined by the molecular characteristics (side chains volume fraction, backbone stiffness) of the studied polymers. All the CN-containing polymers 3b, 5, and 7a exhibit higher fluorescence quantum yield in solid state (50 to 60%), but lower quantum yields (12−40%) in dilute chloroform solution, in total contrast to CN-free polymers 3c, 3d, and 7b. Identical optical, E g opt, and electrochemical band gap energies, E g ec, were obtained for 3b, 3c and 3d with intrinsic self-assembly ability, whereas a discrepancy, ΔE g, was observed in the cases of the fully substituted polymers 5, 7a, and 7b, whose values are dependent on the level of backbone stiffness and length of the side groups combined with the presence or absence of CN units. The incorporation of CN units in 3b and 7a lowers their respective LUMO level by 220 and 350 meV compared to their corresponding CN-free counterparts 3c and 7b, suggesting an improvement of the electron-accepting strength. Polymers 3b and 7a are efficient electron acceptors suitable for photovoltaic application. The experiments indicate that 3b is a better electron acceptor when used together with M3EH−PPV, but transport properties seem to be better for 7a. With 3b, high external quantum efficiencies of up to 23%, an open circuit voltage of up to 1.52 V, and a white light energy efficiency of 0.65% could be realized in bilayer solar cell devices. LED-devices of configuration ITO/PEDOT:PSS/polymer/Ca/Al from 3b, 3c, 7a, and 7b showed low turn-on voltages between 2 and 2.5 V. The CN-free polymers 3c and 7b exhibit far better EL parameters than their corresponding CN containing counterparts 3b and 7a.

Poly(phenylenevinylenes)

“…The energetically favorable pathway leads to the effective hole injection and transport in the respective device. [82,83] The yne-containing CN-PPV 41c is similarly synthesized [86], which exhibits higher film fluorescence but lower EL efficiency than the corresponding CN-free polymer. …”

Synthesis of New Conjugated CNPPV Derivatives Containing Different Lengths of Oligothiophene Units for Organic Solar Cells

“…[17] Cyano-substituted poly[2,5-bis(dodecyloxy)-p-phenylenevinylene]s (CNPPV) with electron-deficient cyano groups on the vinyl units, display high electron affinities and electron-transport properties and have been used as electron acceptors in organic photovoltaic (OPV) devices. [18][19][20] To effectively reduce the bandgap of CNPPV below 2 eV, electron-rich thiophene units with lower aromaticities have been incorporated into the main chain to form a D/A-type polymer. Vanderzande [21,22] and co-A new series of CNPPV derivatives that contain oligothiophenes in the polymer backbone, have been synthesized by Knoevenagel polycondensation.…”

Saturated Red Light‐Emitting Copolymers of Poly(aryleneethynylene)s with Narrow‐Band‐Gap (NBG) Units: Synthesis and Luminescent Properties

“…LUMO level is estimated from the optical-band-gap and HOMO level determined from p-doping onset. Keeping in mind that in some cases, the electrochemical band-gap is not always equal to the optical band-gap, [40] This shows that PFE-BT50 has different electronic configurations other than most of copolymers. This fact is also consistent with the larger blue-shift of PFE-BT50 in UV spectra ( Table 2).…”