title: Computational characterization of low-lying states and intramolecular charge transfers in N-phenylpyrrole and the planar-rigidized fluorazene.
abstract: Low-lying states and intramolecular charge transfers in N-phenylpyrrole (PP) and its planar-rigidized derivative fluorazene (FPP) have been investigated by ab initio methodologies. On the basis of calculations, properties of the excited states and plausible dual-fluorescence mechanisms have been elucidated. Present results show that S2 as a key state is involved in the consecutive photophysical processes. The S2 state is easily populated under excitation. In the polar MeCN solution, S2 can evolve to either a lower-energy locally excited state or a lower-energy solvated intramolecular charge-transfer state (S-ICT). The former emits a normal fluorescence back to the ground state, and the latter is exclusively responsible for the red-shifted fluorescence band. Calculations reveal that the emissive ICT states in both FPP and PP have similar geometric features, an elongated N-phenyl bond, a pyramidal carbon atom linking the pyrrole ring, and a quinonoid phenyl ring. The twisting of molecule around the N-phenyl bond is not necessary for the intramolecular charge transfer. Predicted absorption and emission spectra are in reasonable agreement with the experimental observations.
authors.affiliation: Department of Chemistry, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, China.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Xu
authors.forename: Zexing
authors.initials: Z
authors.lastname: Cao
authors.forename: Qianer
authors.initials: Q
authors.lastname: Zhang