Substituent position-induced color tunability in polymer light-emitting diodes

Abstract

We report substituent position-induced color tunability in polymer light-emitting diodes fabricated with poly[2-{2- or 3- or 4-[(3,7-dimethyloctyl)oxy] phenyoxy}-1,4-phenylenevinylene] (DMOPPPV). When the position of the substituent in DMOP-PPV moves to the ortho, meta, and para sites, the corresponding photo- and electroluminescence spectra shift their peaks to a longer wavelength of about 540, 560, and 585 nm, respectively. We ascribe this to the different degree of steric effect in the backbone for each substituent position. As the substituent position is closer to the main chain, the planarity of the backbone is less conserved, thereby reducing the effective conjugated length of the main chain and broadening the π-π* energy gap.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

“…The position of the substituents also has a marked effect on the emission color. Thus, polymers 73 − 75a with o -, m -, and p -substituted phenoxy side-chains display EL maxima at 541, 560, and 568 nm, respectively. , This red-shift can be explained by a reduction in steric interactions between the alkoxy group and the main chain leading to a more planar chain conformation and thus an increase in conjugation. However, the m -substituted 74 possessed the highest PL efficiency (54% cf .…”