Unraveling the effect of solvents on the excited state dynamics of C540A by experimental and theoretical study

In this work, the excited-state dynamics including intramolecular charge transfer (ICT) and the redshift of C540A have been investigated in a series of solvents on the basis of the Kamlet-Taft solvatochromic parameters (pi*, alpha, beta) using femtosecond transient absorption spectra and systematic theoretical calculation. We demonstrate that the redshift of the emission peak has a linear relationship with the alpha and pi* scales and the effect of the pi* scale is slightly stronger than that of the alpha scale. Meanwhile, the ICT rates can be suggested as relevant to not only the alpha scale but also the pi* scale. Additionally, C540A-AN has proved that the excited state molecules have a unique inactivation mechanism because of the dark feature of the S-1 (CT) state. The valuable mechanistic information gleaned from the excited-state dynamics by the experimental and theoretical study would facilitate the design of organic materials for prospective applications in photochemistry and photobiology.