Structural Order in Conjugated Organic Films Prepared by Catalytic Deprotection of Self-Assembled Polymers

Persistent lamellar ordering, consistent with coplanar stacking of polymer chains, is found for films of poly(3-(2-hydroxylethyl)thiophene) (PHET) obtained by catalytic removal of tetrahydropyran from films of poly(3-(2-(2-tetrahydropyranyloxy)ethyl)thiophene) (PTHPET). Structural ordering appears to be due to H-bonding interactions between terminal hydroxy groups. This morphology is unique for films comprising of short side chain poly(alkylthiophenes), which are usually characterized as being amorphous. The resultant films possess void spaces due to loss of the bulky group and retention of the initial morphology. The formation of additional free volume may explain why this reaction is facile in these materials even though they are semicrystalline. Catalytic removal of tetrahydropyran from copolymer films of PTHPET and 3-hexylthiophene also leads to persistent ordering, but the lamellar framework partially relaxes in some cases so that the interlamellar spacing is reduced. These are metastable structures that become amorphous upon heating to elevated temperatures.