S2 emission from chemically modified BODIPYs.

Novel boron dipyrromethene (BODIPY) derivatives having significant absorption and emission in the longer wavelength region were synthesized. BODIPY showed anomalous S-2 emission from the second excited (S-2) state at shorter wavelength. The photodynamics of the S-2 state was investigated by fluorescence up-conversion and transient absorption spectroscopic measurements. The decay time of the S-2 emission was dependent on the internal conversion and the intersystem crossing process. The assignments of transitions were supported by a theoretical calculation based on the time-dependent density functional theory.