Vibrational and electronic relaxation in MEH-PPV using few cycle pulses

Abstract

• Electronic dephasing time in MEH-PPV is determined as 25 ± 2 fs using a sub 7 fs pulse. • Self-trapping time of a free exciton to form a polaron is measure as 50 ± 23 fs. • Mechanism of real-time dynamic mode-coupling among vibration modes is clarified. • Energy ladder descent process in vibration modes is clarified by a moment method. The electronic population decay time is determined to be about 500 fs in (poly-[2-methoxy-5-(2′-ethyl-hexyloxy)- p -phenylenevinylene] (MEH-PPV) using 5.7 fs pulses. The ultrafast electronic dephasing time and the self-trapping time of free exciton to form an exciton polaron is determined as 25 ± 2 fs and 50 ± 23 fs, respectively. Real-time spectrogram analysis reveals dynamic mode coupling among the high-frequency and low-frequency modes. The energy-ladder descent vibrational process is clarified using the first moment of the difference absorption spectrum. The phase relaxation time is calculated from the widths of the Fourier spectra of several strongly coupled modes.