title: Switching of the triplet excited state of rhodamine/naphthaleneimide dyads: an experimental and theoretical study.
abstract: Rhodamine-bromonaphthaleneimide (RB-NI) and rhodamine-bromonaphthalenediimide (RB-NDI) dyads were prepared for switching of the triplet excited states. Bromo-NI or bromo-NDI parts in the dyads are the spin converters, i.e., the triplet state producing modules, whereas the RB unit is the acid-activatable electron donor/energy acceptor. NI and NDI absorb at 359 and 541 nm, and the T1 state energy levels are 2.25 and 1.64 eV, respectively. RB undertakes the reversible spirolactam (RB-c) ↔ opened amide (RB-o) transformation. RB-c shows no visible light absorption, and the triplet-state energy level is ET1 = 3.36 eV. Conversely RB-o shows strong absorption at 557 nm, and ET1 is 1.73 eV. Thus, the acid-activated fluorescence-resonance-energy-transfer (FRET) competes with the ISC of NI or NDI. No triplet state was observed for the dyads with nanosecond time-resolved transient absorption spectroscopy. Upon addition of acid, strong fluorescence and long-living triplet excited states were observed. Thus, the producing of triplet state is acid-activatable. The triplet state of RB-NI is localized on RB-o part, whereas in RB-NDI the triplet state is delocalized on both the NDI and RB-o units. The ISC of spin converter was not outcompeted by RET. These studies are useful for switching of triplet excited state.
authors.forename: Xiaoneng
authors.initials: X
authors.lastname: Cui
authors.forename: Jianzhang
authors.initials: J
authors.lastname: Zhao
authors.forename: Zhangrong
authors.initials: Z
authors.lastname: Lou
authors.forename: Shujing
authors.initials: S
authors.lastname: Li
authors.forename: Huijian
authors.initials: H
authors.lastname: Wu
authors.affiliation: §State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences (CAS), Dalian 116023, P. R. China.
authors.forename: Ke-Li
authors.initials: KL
authors.lastname: Han