Exciton Coupling Enhancement in the Relaxed Excited State

The steady-state and photoinduced dynamical optical properties of two squaraine-bodipy dye conjugates are the focus of this work. While the squared absorption transition moments of the dye conjugates can be traced back in an additive way to the constituents of the conjugates, this is not possible for the squared fluorescence transition moments. We suggest an enhancement of electronic coupling in the relaxed excited state to be responsible for this observation. Transient absorption and fluorescence upconversion experiments with femtosecond-time resolution give insight into the relaxation phenomena of the dye conjugates, in particular concerning the relaxation within the exciton manifold.