Non-equivalent local excitations and conformation dependent charge transfer in N,N-dimethylethylenediamine

The discrimination of local excitation sites in multi-charge-center molecular systems remains a long-standing challenge and is rarely explored. Herein, non-equivalent local excitations of two distinct 3s Rydberg states (3s1 and 3s2, as excited from the N1 and N4 atoms, respectively) in two-charge-center N,N-dimethylethylenediamine and their ensuing conformation-dependent charge transfer dynamics have been observed by femtosecond time-resolved photoelectron spectra. In particular, following local excitation at N4, the 3s2 state structurally evolves away from the Franck-Condon region driven by charge redistribution from N1 to the hole of N4 via through-bond interaction, leading to the 3s1 and 3s2 states being energetically indistinguishable after 300 fs. The preferential charge stabilization at N4 is observed, exhibiting a new paradigm of charge localization. Concurrently, the 3p state undergoes internal conversion to 3s_h and 3s_l states and approaches a dynamic conformation equilibrium (3s_h/3s_l = 61%:39%) within about 1.1 ps. This work provides new insight into the understanding of charge localization and transfer phenomena in biologically relevant molecular systems with multiple charge centers.