Femtosecond Fluorescence Anisotropy Kinetics as a Signature of Ultrafast Electronic Energy Transfer in Bichromophoric Molecules

Abstract

Ultrafast time resolved fluorescence anisotropy decay measurements were performed to gain insight into the energy gap dependence of donor-acceptor inter-chromophoric coupling within one supra-molecule. Three new compounds, each consisting of two semi-rigidly linked and strongly coupled chromophores, were designed and synthesized for this study. Their general structure is donor-spacer-acceptor, where "donor" is phenylamino, pyrenylamino, or benzanthronylamino moiety, and acceptor is aminobenzanthrone. While being similar structurally, the compounds differ significantly in the excitation energy difference of the two chromophores in a supra-molecule. Experimental data show an ultrafast initial fluorescence emission anisotropy decrease (within less then 1 ps) when the excited state energies of the interacting chromophores are close to each other or equal. No such fast fluorescence anisotropy dynamics is observed for a compound with a large energy gap.

Novel 1- and 9-aminoanthracene/3-aminobenzanthrone bichromophores exhibiting through-bond excitation energy transfer

“…For D-T-A bichromophore where D is 1-aminopyrene and A is 3-aminobenzanthrone, very efficient EET was found which takes place on the subpicosecond time scale, i.e. much shorter than it could correspond only to FRET [9,10]. For bichromophores bearing 3-aminobenzanthrone acceptor moiety we have found the excited singlet states connected with the CT from donor moiety to the acceptor; depending on the solvent polarity, this state may be responsible for the dramatic changes of the fluorescence quantum yield.…”

Ultrafast intramolecular electronic energy transfer in rigidly linked aminopyrenyl–aminobenzanthronyl dyads—a femtosecond study

“…In this case the oscillator strength of the S n ' S 1 transition would have to be about 30% larger than that of the S n ' S x transition. The S 1 -state can be identified with the long-lived fluorescent state observed previously 30,31 Alternatively, both S 1 and a dark S x -state could be populated by EET with an overall rate coefficient of B3 Â 10 12 s À1 and a branching ratio of 3 : 1 in favour of the S 1 -state. Subsequently, one would observe S 1 ' S x internal conversion at a rate of B2.5-5 Â 10 11 s À1 .…”

The synthesis of bi- and trichromophoric dyes bearing an s-triazinyl ring spacer

“…The synthesis of compounds 5 and 7 was already described by Fidler et al [2]. In the same way as described for 2 and 6, we modified this procedure by using an autoclave.…”

“…Fidler et al [2] reported on the photo-physics of a semi-rigidly linked bichromophoric compound consisting of 1-aminopyrene and 3-aminobenzanthrone chromophoric sub-units connected by a chlorotriazinyl spacer.…”