Dibenzosilol Polymers, Their Preparation and Uses

Abstract

A polymer containing an optionally substituted repeat unit of formula (I) wherein each R is the same or different and represents H or an electron withdrawing group, and each R1 is the same or different and represents a substituent.

Description

FIELD OF THE INVENTION [0001] The invention relates to polymers for electronic and optical applications and the synthesis thereof. BACKGROUND OF THE INVENTION [0002] Organic semiconductors are attracting increasing attention across a wide range of applications due to their advantageous electronic properties and their processability. One class of opto-electrical devices is that using an organic material for light emission (an organic light-emissive device or “OLED”) or for light absorption for the purpose of power generation or light detection (a photovoltaic device). The basic structure of these devices is a semiconducting organic layer, sandwiched between a cathode for injecting or accepting negative charge carriers (electrons) and an anode for injecting or accepting positive charge carriers (holes) into or from the organic layer. For example, an OLED is typically fabricated on a glass or plastic substrate coated with a transparent first electrode such as indium-tin-oxide (“ITO”). ...

AI Technical Summary

Benefits of technology

[0050] As outlined above, linkage of dibenzosilole repeat units according to the invention through their 2- and 7-positions maximises conjugation of polymer chains comprising these repeat units. However, the present inventors have found that non-2,7-linked dibenzosiloles possess a wider bandgap than corresponding 2,7-linked dibenzosiloles and at the same time retain a desirable high electron affinity. Moreover, non-2,7-linked dibenzosiloles have been found to possess a higher triplet energy level than corresponding 2,7-linked dibenzosiloles and as such may serve as the host material for a wider range of fluorescent or phosphorescent dopants.

[0060] The present inventors have found that polymers comprising dibenzosilole repeat units function very effectively as host materials for luminescent dopants.

Problems solved by technology

A difficulty encountered with blue electroluminescent polymers to date is that their lifetime (i.e. the time taken for brightness to halve from a given starting brightness at fixed current) tends to be shorter than that of corresponding red or green materials.

It is therefore possible that materials comprising these lower electron affinities are less electrochemically stable and so more prone to degradation.

A blue electroluminescent material having a higher electron affinity than polyfluorenes or a material capable of injecting electrons into blue electroluminescent polymers is therefore desirable, however increasing the electron affinity of a wide bandgap material will tend to result in a smaller bandgap thus making the material less suitable as a blue emitter or as an electron transporting material for a blue emitter.

A further drawback of polyfluorenes is that blue electroluminescent polyfluorenes have a tendency to shift over time towards longer wavelengths, i.e. towards a redder colour of emission.

Although these alkoxy groups are significant in monomer synthesis, they are likely to cause repeat units derived from such monomers to suffer from steric interference with adjacent repeat units resulting in a twist in the polymer backbone and loss of conductivity.

A further drawback of polymers derived from monomers (B) and (C) is that the phenyl and methyl groups of these monomer do not afford solubility in common organic solvents such as xylene.

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