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

Abstract

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.