Switching resonance character within merocyanine stacks and its impact on excited-state dynamics

In this study, the optical properties and excited-state dynamics of unique self-assembled donor-acceptor (DA) merocyanine dye stacks from dimer up to octamer, prepared via dipole-dipole interactions, are reported in terms coherent exciton formation an excimer-like state. Our findings based on steady-state absorption/emission, time-resolved fluorescence, transient absorption (anisotropy) measurements, including wavepacket analysis quantum mechanical calculations. Coherent torsional motions-restricted rapidly localizes into weakly emissive state, by shortening inter-moiety distance changing bond-length alternation pattern. The inner moiety, having two neighboring units, has a reversed resonance character (non-polar (N) < zwitterionic (Z)) compared with outer moiety (N > Z) ground This difference led conclusions: (1) tetramers octamers exhibit different features state than dimer, (2) slower localization due enhanced homogeneity (six inner-moieties) (two moieties).