Femtosecond coherent wavepacket motion in an ultrafast electron transfer system composed of naphthacene derivative in an electron donating solvent

• Femtosecond transient absorption measurements were carried out for naphthacene derivative.
• In an inert solvent, 1-chloronaphthalene, both the intensity and the wavelength of the stimulated emission (SE) was modulated by the wavepacket motion.
• In an electron donating solvent, N,N-dimethylaniline, the SE intensity was quickly diminished and only the wavelength of SE was modulated.

Coherent wavepacket motions of 5,12-bis(phenylethynyl)-naphthacene (BPEN) in an inert solvent, 1-chloronaphthalene (1-CN), and in an electron donating solvent, N,N-dimethylaniline (DMA) were compared by femtosecond white-light supercontinuum transient absorption (WC-TA) spectroscopy. In the inert solvent, 1-CN, both the intensity and the wavelength of the stimulated emission (SE) was modulated by the wavepacket motion, i.e., the maximum of the SE spectrum exhibited a repetitive movement between longer and shorter wavelengths (frequency-modulation) and the SE intensity was stronger at shorter wavelengths (amplitude-modulation). While in the electron donating solvent, DMA, the intensity was quickly diminished and only the frequency-modulation remained. The ultrafast electron transfer (ET) occurring in a few picosecond range rapidly diminishes the population in the vicinity of the Franck–Condon region and the wavepacket motion was no longer capable of recovering the SE intensity.