Linker Effects on Exciton Migration and Charge Transfer of

Linker Effects on Exciton Migration and Charge Transfer of Conjugated Polymers Qiquan Qiao, Center for Advanced Photovoltaics, Electrical Engineering, South Dakota State University, Brookings, SD 57007

N

S

N C12H25

C12H25

1.0

DA1

N

S

n

N C12H25

C12H25

DA2

S

n N

S

N

C12H25

C12H25 S

DA3 n

Fluorescence intensity (a. u.)

S

0.5

DA1 λem=580 nm

0.0 1.0 0.5

DA2 λem=640 nm

0.0 1.0 0.5 0.0

DA3 λem=580 nm 0

10

20

30

40

Time (ps)

The femtosecond up-conversion fluorescence measurement showed that DA1 and DA3 exhibited a rise process for the energetically downhill excitonic energy transfer (EET) in a timescale of sub-ps to several ps, while DA2 exhibited a decay process in such downhill EET. DA2 showed the shortest time constant of ~ 4.6 ps for torsional relaxation. This suggested that the vinylene linker has the fastest torsional relaxation from a flexible ground-state structure to a more rigid planar geometry, which may reduce conformational defects and improve exciton migration.