•Energy decomposition analysis elucidates the nature of P3HT backbone flexibility.•Weak π conjugation in Br-P3HT is attributed to steric hindrance of bromo group.•The steric hindrance causes out-of-plane backbone torsion and spectral blue shift.•A torsional defect originating from bromination breaks the π conjugation.In poly(3-hexylthiophene) (P3HT), it is suggested that bromination disturbs the π conjugation and reduces the carrier mobility. To investigate the deconjugation mechanism, we theoretically studied a key flexibility of the Br-P3HT backbone, namely inter-ring SCCS dihedral torsion, in terms of potential energy curve, geometry-based aromaticity index, and decomposed energies of inter-monomer interaction. The linkage between bromination and the excitation energy was also investigated. We concluded that steric repulsion due to bulky bromo group can cause out-of-plane SCCS torsion of Br-P3HT and consequent shortening of the conjugation length, not electronic substituent effect, leads to blue shift of the S0→S1 excitation energy.Download high-res image (83KB)Download full-size image

A low temperature in situ Raman spectroscopic method was developed for the detection of unstable intermediates in electro-organic chemistry. It was effective for monitoring the generation of ArS(ArSSAr)+ by the electrochemical oxidation of ArSSAr (Ar = p-FC6H4) in Bu4NBF4/CH2Cl2 at 195 K. The intensity of a Raman band at 427 cm−1, which is attributable to the S–S vibration of ArS(ArSSAr)+, increased with an increase in the electricity until 2/3 F of the electricity was consumed, whereas decreased with a further increase in the electricity indicating the decomposition of ArS(ArSSAr)+.

A low temperature in situ Raman spectroscopic method was developed for the detection of unstable intermediates in electro-organic chemistry. It was effective for monitoring the generation of ArS(ArSSAr)+ by the electrochemical oxidation of ArSSAr (Ar = p-FC6H4) in Bu4NBF4/CH2Cl2 at 195 K. The intensity of a Raman band at 427 cm−1, which is attributable to the S–S vibration of ArS(ArSSAr)+, increased with an increase in the electricity until 2/3 F of the electricity was consumed, whereas decreased with a further increase in the electricity indicating the decomposition of ArS(ArSSAr)+.