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Analysis of State-Specific Vibrations Coupled to the Unidirectional Energy Transfer in Conjugated Dendrimers

2012; American Chemical Society; Volume: 116; Issue: 40 Linguagem: Inglês

10.1021/jp301293e

1520-5215

Miguel A. Soler, Adrián E. Roitberg, Tammie Nelson, Sergei Tretiak, Sebastian Fernandez‐Alberti,

Nonlinear Optical Materials Research

The nonadiabatic excited-state molecular dynamics (NA-ESMD) method and excited-state instantaneous normal modes (ES-INMs) analyses have been applied to describe the state-specific vibrations that participate in the unidirectional energy transfer between the coupled chromophores in a branched dendrimeric molecule. Our molecule is composed of two-, three-, and four-ring linear poly(phenyleneethynylene) (PPE) units linked through meta-substitutions. After an initial laser excitation, an ultrafast sequential S3 → S2 → S1 electronic energy transfer from the shortest to longest segment takes place. During each Sn → Sn–1 (n = 3, 2) transition, ES-INM(Sn) and ES-INM(Sn–1) analyses have been performed on Sn and Sn–1 states, respectively. Our results reveal a unique vibrational mode localized on the Sn state that significantly matches with the corresponding nonadiabatic coupling vector dn,(n–1). This mode also corresponds to the highest frequency ES-INM(Sn) and it is seen mainly during the electronic transitions. Furthermore, its absence as a unique ES-INM(Sn–1) reveals that state-specific vibrations play the main role in the efficiency of the unidirectional Sn → Sn–1 electronic and vibrational energy funneling in light-harvesting dendrimers.