A Negative-Type Photosensitive Poly(3-hexylthiophene) with Cross-Linker and Photoacid Generator

-Conjugated polymers ( CPs) have received great attention for their potential application to electronic devices derived from their semiconductive property. Among them, poly(3-hexylthiophene) (P3HT) is of great interest because of easy preparation, high charge mobility, and high processability. Based on these benefits, P3HT has been used in a wide variety of electronic devices, such as organic solar cells, organic fieldeffect transistors (OFETs), and sensors. Generally, a micro-patterned P3HT is fabricated by the microcontact printing (mCP) method with a poly(dimethylsiloxane) stamp. However, this method requires complicated operation resulting in low productivity. To overcome this problem, direct patterning onto polythiophenes based on a photolithographic method is highly required. Direct patterning onto P3HT was demonstrated when an exposed area became insoluble due to crosslinking of an alkyl chain under irradiation with UV light. However, the cross-linking of P3HT by irradiation required a huge exposure dose. Recently, efficient patterning methods of polythiophene derivatives were reported. These methods require multi-step reactions for the preparation of matrix polymers. In this paper we propose a new, simple patterning process of P3HT by combining hexamethoxymethylmelamine (CYMEL) as a cross-linker and diphenyliodonium-9,10-dimethoxyanthracene-2-sulfonate (DIAS) as a photoacid generator (PAG). The structures of the chemicals are shown in Figure 1. P3HT was easily synthesized by oxidation polymerization and a photosensitive P3HT was prepared from a mixture of each component. In the exposed area, the aromatic rings of P3HT react with a carbocation formed from CYMEL and cross-link with each other in the presence of acids from DIAS by irradiation. This eletrophilic substitution reaction is novel to the best of our knowledge, although the similar reaction based on arylene compounds has been reported. High-resolution patterns of CPs are expected from this approach.