Synthesis and characterization of naphthyl‐substituted poly(p‐phenylenevinylene)s with few structural defects for polymer light‐emitting diodes

Abstract

A series of naphthyl‐substituted poly(p‐phenylenevinylene)s (2N‐PPV, 4N‐PPV, and NAP‐PPV) has been synthesized and characterized by Fourier transform IR, 1H NMR, and elemental analysis. The polymers possess excellent solubility, high molecular weights, good thermal stability, and high photoluminescence efficiencies. Thermogravimetric analysis reveals the onset of degradation to be 347, 301, and 306 °C for 2N‐PPV, 4N‐PPV, and NAP‐PPV, respectively. The differential scanning calorimetry investigation gives the respective glass‐transition temperature values of 118, 135, and 141 °C. The UV and photoluminescence spectra measurements reveal that the polymers exhibit similar optical properties, indicating that side‐chain substitution has little effect on the optical properties of this series of polymers. Proton NMR measurement of the signal due to tolane–bisbenzyl defects at around 2.7 ppm indicates that all the polymers have negligible amounts of tolane–bisbenzyl defects along the polymer main chain as a result of the steric bulk imposed by the naphthalene side chain. The highest occupied and lowest unoccupied molecular orbital energy levels of the polymers are investigated through cyclic voltammetry. Polymer light‐emitting diodes utilizing the polymers as the emissive layer with a configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene)/polymer/Ba/Al are fabricated and evaluated. The diodes emit blue‐green to yellow‐green light with maximum peaks at 518, 542, and 486 nm for 2N‐PPV, 4N‐PPV, and NAP‐PPV, respectively. The respective turn‐on electric fields of the diodes are 0.84, 0.69, and 0.83 MV/cm and the respective maximum external quantum efficiencies are 0.08, 0.54, and 0.02%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1647–1657, 2004

New deep blue light emitting copolymer containing fluorene, carbazole, and dialkoxynaphthalene

“…19,20 It was also found that the introduction of rigid and bulky naphthyl group improved thermal stability with higher glass-transition temperatures and prevented the generation of excimers due to molecular interaction. [21][22][23] Therefore, it creates a highly efficient material.…”

Synthesis and characterization of organic light-emitting copolymers containing naphthalene

“…[1][2][3][4][5][6][7][8] They have been developed and applied due to remarkable advantages such as their self-emission, low operating voltage, color tunability, wide viewing angle, fast switching time, easy fabrication at low cost, and potential applications to full color flat panel displays and flexible displays. [9][10][11][12][13][14][15] Despite their many advantages, there are several issues that must be resolved, such as the device lifetime and luminescence. These are related to imbalanced charge injection/ transporting, excimer/exciplex or aggregate formation, and structural defects in the polymers that result from head-head and tail-tail linkage during Gilch polymerization.…”

“…These are related to imbalanced charge injection/ transporting, excimer/exciplex or aggregate formation, and structural defects in the polymers that result from head-head and tail-tail linkage during Gilch polymerization. [15][16][17][18][19][20][21][22][23] These conditions lead to a low luminescent efficiency and short lifetime of PPV-derived LEDs. To resolve the structural defects, the authors and other groups have investigated naphthylsubstituted poly(p-phenylenevinylene)s (N-PPVs); 15,24 it was found that the introduction of a bulky naphthyl side chain can cause the polymers to impose even great steric hindrance, which leads to negligible structural defects due to the asymmetric structure and the improved thermal stability with higher glass-transition temperatures.…”

“…It also causes an increase in the solubility and prevents the generation of excimers due to molecular interaction. 15,[22][23][24][25][26][27][28][29][30][31][32][33][34]36,37 Therefore, it creates a highly efficient material.…”

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“…PPV has many good characteristics such as good charge carrier mobility, formation of high molecular weight polymers, soluble in common solvents, processability, and highly luminescence intensity which make PPV more attractive than many other conjugated systems 22. Bulky‐PPVs were reported using cycloalkoxyl,23–25 adamantyl,26, 27 cholestanyl,28, 29 aryloxy,30–33 and inorganic pendants like silyl34 and silsesquioxane35, 36 in the conjugated backbone. However, most of the successful bulky‐PPVs were found insoluble or partially soluble in common solvents, which hampered their processability, complete structural‐characterization, and so forth 26, 28.…”