Structural and optical properties of inherently chiral polythiophenes: a combined CD-electrochemistry, circularly polarized luminescence, and TD-DFT investigation

Circular dichroism (CD) and ultraviolet absorption (UV) spectra of films obtained by electrochemical polymerization of inherently chiral 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene (T4-BT2) are taken during electrochemical polarization cycles. Besides the bisignate CD features in the near UV range recorded at zero potential, new features in the visible-near-infrared range are observed under increased applied potential. Results are interpreted with the help of static and time-dependent (TD) density functional theory (DFT) calculations, which shed light on the structural and electronic properties of neutral and charged oligomers (from monomers to tetramers) and reproduce UV and CD spectra satisfactorily. Furthermore, properties of the excited state of T4-BT2 monomers in solution are enlightened by combining circularly polarized luminescence (CPL) measurements with TD-DFT calculations.