The conductivity and nonlinear optical properties of isonaphtothiophene (INT)n are investigated by quantum chemical techniques. The conducting properties of (INT)n are examined by density of states (DOS) and local DOS analyses. As the chain length n increases, the geometrical conformations of (INT)n changed, and the energy gap suddenly decreases. The energy potentials and rotation effect are explored to determine the most preferred stable structures. The geometrical and intrinsic charge character are analyzed by UV/vis/NIR spectra and confirmed by frontier orbital analysis. Interestingly, the (hyper)polarizabilities of (INT)n oligomers increase sharply as the chain length increased. Additionally, the importance of the side β double bonds effect on the structural transformation is detected by a new quantum chemical technique resulting in a potential polymer conductor that can be controlled by modifying its side chains.
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