Tortional strain

Cedergren-Zeppezauer E, Samama J-P, Eklund H (1982) Crystal structure determinations of coenzyme analogue and substrate complexes of liver alcohol dehydrogenase Binding of 1,4,5,6-tetrahydronicotin-amide adenine dinucleotide and trans-4-(N,N-dimethylamino)cinnam-aldehyde to the enzyme. Biochemistry 21 4895-4908 Cherest M, Felkin H, Prudent N (1968) Tortional strain involving partial bonds. The stereochemistry of the lithium aluminium hydride reduction of some simple open-chain ketones. Tetrahedron Lett 2199-2204... 

Since the conjugation length is dependent on the overlap of neighboring thiophene rings, it can easily be influenced by the introduction of tortional strain along the polymer backbone. 

The number, type, and placement of side chains along the backbone can all contribute to increased steric effects and thus tortional strain. 

Ahn, N. T. Eisenstein, O. Theoretical Interpretation of 1,2-Asymmetric Induction. The Importance of Antiperiplanarity Nouv. J. Chim. 1977, 1, 61-70. Cherest, M. Felkin, H. Prudent, N. Tortional Strain Involving Partial Bonds. The Stereochemistry of the Lithium Aluminum Hydride Reduction of Some Simple Open-Chain Ketones Tetrahedron Lett. 1968,10, 2199-2204. 

Figure 2.52. Illustration of various types of loads (stresses), which result in material strain. Shown are (a) tensile stress, (b) compressive stress, (c) shear stress, and (d) tortional stress. Reproduced with permission from Callister, W. D. Materials Science and Engineering An Introduction, 7th ed., Wiley New York, 2007. Copyright 2007 John Wiley Sons, Inc.

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