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.