Broadband femtosecond transient absorption and two-dimensional electronic spectroscopy of donor-acceptor substituted perylene

초록

Photoinduced charge transfer (CT) is one of the important events observed in various photo-sensitizers, ranging from biological photosynthetic assemblies to artificial light harvesting systems. Donor?acceptor (DA) conjugated systems, facilitating ultrafast charge separation through exciton splitting, have been employed to improve the efficiency of solar-energy conversion in the various light harvesting modules and optovoltaic materials. To comprehend the underlying photophysics of DA conjugation system, we investigated the photoinduced CT dynamics for the newly synthesized molecular system consisted of two moieties of diphenylamine acting as the electron donating group and perylene acting as the electron accepting group. We performed the broadband transient absorption spectroscopic (TA) measurements where the excitation wavelength is tuned either for the electronic transition to local singlet excited state at 498 nm or to lowest state at 575 nm. To control the polarity of solvent affecting the photochemical mechanism, the various solvents were chosen such as cyclohexane (CHX), tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO). In the polar solvent of DMSO, the formation of new excited state absorption (ESA) around 575 nm is observed under the excitation of 498 nm, while this spectral feature is absent in the non-polar solvent of CHX. In the transition to the lowest singlet excited state, the ESA feature around 575 nm is not formed, but the ESA signal corresponding to the lowest excited state shows the monotonic decay. Based on these observations, the formation of new ESA band can be originated from the photoinduced CT intersystem crossing (CT-ISC) accompanying the transition from the high-lying singlet excited state to triplet state. In addition, we implemented the two-dimensional electronic spectroscopy (2D-ES) experiment for the perylene derivative dissolved in DMSO. Spectrally-resolved cross peak occurs in the off-diagonal region of absorptive 2D-ES spectra