Excitation wavelength dependent ICT character and ISC efficiency in a photocleavage agent of 1-aminoanthraquinone

Anthraquinone derivatives have been widely used as photocleavage agents and dyes. Here, photoinduced excited state intramolecular charge transfer (ICT) dynamics of 1-aminoanthraquinone in ethanol are studied by femtosecond transient absorption (fs-TA) spectroscopy and quantum chemical (QC) calculations. Four decay associated difference spectra and corresponding lifetime components were obtained by singular value decomposition and global fitting analysis from the fs-TA spectra. The QC calculations prove that the S 1 state has obvious ICT character. Planar ICT (PICT) and twisted ICT (TICT) reaction coordinates are observed. On the PICT coordinate, vibrational relaxation (VR) and intersystem crossing (ISC) processes are observed. The ISC efficiency is dependent on excitation wavelength, which elucidates that T′ 2 state participates in the ISC process on a higher-level than the S′ 1 state. On the TICT coordinate, the TICT process is dependent on excitation wavelength, which elucidates a direct experimental evidence of an energy barrier in excited state TICT potential energy.