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.