Charge transfer and separation are important processes governing numerous chemicalreactions.Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry.H erein, we report the discovery of anew charge-transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems,t he donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 908 8 intramolecular rotation. TICS systems thus exhibit charge shuttling.T ICSs exist in several chemical families of fluorophores (sucha sc oumarin, BODIPY,a nd oxygen/carbon/ silicon-rhodamine), and could be utilized to construct functional fluorescent probes (i.e., viscosity-or biomoleculesensing probes). The discovery of the TICS process expands the current perspectives of charge-transfer processes and will inspire future applications.Photo-induced charge transfer and separation is af undamental process, [1] responsible for photosynthesis, [2] and has applications in solar cells, [3] photocatalysis, [4] and fluorescence probes. [5] Greater understanding of charge-transfer and separation processes is thus important to aid in improving photochemistry.H owever,o wing to fast photon-absorption rates and short excited state lifetime,u nderstanding charge transfer and separation at amolecular level remains asignificant challenge.This challenge could be overcome if the model systems under study emit fluorescence (or other forms of luminescence). [1b] Thec hanges in fluorescence output (for example, intensity,l ifetime,a nd wavelength) provide critical information on the thermodynamics and kinetics of the chargetransfer and separation processes in the excited state,a long with ap lethora of other important photo-physical and -chemical information. Accordingly,s tudies have been con-ducted to investigate charge-transfer and separation mechanisms in fluorescent compounds. [6] It has been widely known that the intramolecular charge transfer (ICT) could be modulated via adjusting the "push-pull" effect in acompound consisting of an electron-donating group (EDG) and/or an electron-withdrawing group (EWG). [7] In such compounds, ICT is further enhanced upon photoexcitation. In particular, in al andmark study,G rabowski and co-workers proposed that quasi-rigid donor-acceptor (D-A) compounds could undergo approximately 908 8 intramolecular twisting in the excited state,greatly reinforcing charge transfer and resulting in ac harge-separated state (D + -A À ). [8] They named this mechanism twisted intramolecular charge transfer (TICT; Figure 1a). Rationalization of the TICT mechanism [9] has greatly facilitated the development of many functional materials and devices,s uch as bright and photostable fluorophores, [10] dark quenchers, [11] viscosity sensors, [12] and polarity sensors. [6b] Notably,c harge-transfer and separation processes in both the ICT and TICT states are unidirectional, i.e., from the donor (D) to the acceptor (A) upon photoexcitation.In this study,w er...

No abstract

Charge transfer and separation are important processes governing numerous chemicalreactions.Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry.H erein, we report the discovery of anew charge-transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems,t he donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 908 8 intramolecular rotation. TICS systems thus exhibit charge shuttling.T ICSs exist in several chemical families of fluorophores (sucha sc oumarin, BODIPY,a nd oxygen/carbon/ silicon-rhodamine), and could be utilized to construct functional fluorescent probes (i.e., viscosity-or biomoleculesensing probes). The discovery of the TICS process expands the current perspectives of charge-transfer processes and will inspire future applications.Photo-induced charge transfer and separation is af undamental process, [1] responsible for photosynthesis, [2] and has applications in solar cells, [3] photocatalysis, [4] and fluorescence probes. [5] Greater understanding of charge-transfer and separation processes is thus important to aid in improving photochemistry.H owever,o wing to fast photon-absorption rates and short excited state lifetime,u nderstanding charge transfer and separation at amolecular level remains asignificant challenge.This challenge could be overcome if the model systems under study emit fluorescence (or other forms of luminescence). [1b] Thec hanges in fluorescence output (for example, intensity,l ifetime,a nd wavelength) provide critical information on the thermodynamics and kinetics of the chargetransfer and separation processes in the excited state,a long with ap lethora of other important photo-physical and -chemical information. Accordingly,s tudies have been con-ducted to investigate charge-transfer and separation mechanisms in fluorescent compounds. [6] It has been widely known that the intramolecular charge transfer (ICT) could be modulated via adjusting the "push-pull" effect in acompound consisting of an electron-donating group (EDG) and/or an electron-withdrawing group (EWG). [7] In such compounds, ICT is further enhanced upon photoexcitation. In particular, in al andmark study,G rabowski and co-workers proposed that quasi-rigid donor-acceptor (D-A) compounds could undergo approximately 908 8 intramolecular twisting in the excited state,greatly reinforcing charge transfer and resulting in ac harge-separated state (D + -A À ). [8] They named this mechanism twisted intramolecular charge transfer (TICT; Figure 1a). Rationalization of the TICT mechanism [9] has greatly facilitated the development of many functional materials and devices,s uch as bright and photostable fluorophores, [10] dark quenchers, [11] viscosity sensors, [12] and polarity sensors. [6b] Notably,c harge-transfer and separation processes in both the ICT and TICT states are unidirectional, i.e., from the donor (D) to the acceptor (A) upon photoexcitation.In this study,w er...

No abstract