Thiophene-based oligomers are a boundless class of organic semiconductors and starting materials for the preparation of electroactive films. Current molecular design strategies in this field address a trade off between two key requirements: branching, to achieve the required solubility for industrial processing, and planarity, to achieve the highest possible conjugation efficiency. In particular, our recent investigations on spider-like oligothiophenes^1,2 have shown that the electronic properties of these molecules do not depend on the overall number of thiophene moieties but on the number of (i) conjugated thiophene moieties in the longest α,α'-linked chain and (ii) "nodes", i.e. distorsions from planarity, along the same chain.

In most cases, the presence of nodes is regarded as an undesirable feature, reducing the effective conjugation length. However, the intrinsic 3D character of the nodes can be useful when employing these molecules as starting compounds for electropolymerization.

A good example is provided by our 2,2’-bis(2,2’-bithiophene-5-yl)-3,3’-bi-1-benzothiophene (shown in Figure). It consists of two identical, approximately planar moieties, each having one terminal α thiophene position available for polymerization, with a central node. From the electroche­mical point of view, this structure implies the presence of two equal, slightly interacting conjugated systems, each one being approximately equivalent to a α-terthiophene. Calculations have shown the central node corresponds to a 70° angle and the energy barrier sufficiently high to yield two stable enantiomers, an attractive feature in the perspective of obtaining optically active conducting films devoid of stereocenters. 

Consistently with its intrinsic 3D nature, this molecule electropolymerizes very rapidly and regularly, a behaviour steadily maintained even after many cycles. This feature can be advantageously exploited to promote 3D copolymerization with monomers having useful functional properties, but being intrinsically able to yield only 2D films. Several examples will be presented, including the preparation of a melamine-templated molecularly imprinted polymer (MIP) film yielding very good performance as a recognition element of a selective piezomicrogravimetric chemosensor.³

1.   T. Benincori, M. Capaccio, F. De Angelis, L. Falciola, M. Muccini, P. Mussini, A. Ponti, S. Toffanin, P. Traldi, F. Sannicolò, Chem. Eur. J. 2008, 14, 459-471.

2.   T. Benincori, V. Bonometti, F. De Angelis, L. Falciola, M. Muccini, P. Mussini, T. Pilati, S. Toffanin, G. Rampinini, F. Sannicolò, 2009, in preparation.

3.   A. Pietrzyk, W. Kutner, R. Chitta, F. D’Souza, F. Sannicolò, P. R. Mussini, 2009, submitted.

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2. Molecularly imprinted polymer (MIP) chemosensors for surface plasmon resonance (SPR) and differerntial pulse voltammetry (DPV) determination of melamine
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