Selective Manipulation of Low-Frequency Modes in Conjugated Polymers via Chirped Optical Frequency Combs

Controlling femtosecond vibronic dynamics in π-conjugated polymers is essen- tial for advancing optoelectronic material design. However, ultrafast spectro- scopic studies to elucidate the complex interplay of electronic and vibrational dynamics in these systems focused on the impact of high-frequency vibra- tions. Here we combine experiment and theory to demonstrate that ultrafast control over the vibronic dynamics involving a low-frequency mode in poly(3- hexylthiophene) is possible via a photoluminescence-detected chirp-dependent double-pump approach. By chirping one of the pump pulses, we show that the temporal ordering of resonant frequency components can be used to engineering the initial vibronic coherence induced in the system. Particularly, the spectro- scopic signals reveal distinct symmetry properties as a function of inter-pulse delay and chirp, i.e., delay and chirp can be used to manipulate quantum beats associated to the system’s vibronic dynamics. Importantly, our signals highlight quantum dynamical features associated to low-frequency vibrational modes in the conjugated polymer. High-frequency modes, despite being optically active, remain undetected. Last, we show that tuning the pulses’ central wavelength can be used to manipulate the symmetry and phase information in the signals. Simulations show that the effective interference between the phase of the pump pulses and the photoinduced vibronic wavepacket determines the evolution and symmetry of the delay- and chirp-dependent signals. Our results establish chirp-dependent time-resolved spectroscopy as a powerful control tool to selective manipulate low- frequency vibronic dynamics in conjugated polymers. The interplay of chirp and delay exposes a coherent-control landscape inaccessible to traditional coherent four-wave mixing spectroscopies, opening new avenues for chirp-driven quantum control in excitonic materials.