A Photoexcitation‐Induced Twisted Intramolecular Charge Shuttle

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...

A Unified Push–Pull Model for Understanding the Ring-Opening Mechanism of Rhodamine Dyes

“…We also performed a benchmark study to ensure the reliability of our computational method (Figures S1 and S2). Previous reports have also validated the reliability of the M062X functional in studying the geometric and electronic structures of organic dyes. ,, …”

“…Previous reports have also validated the reliability of the M062X functional in studying the geometric and electronic structures of organic dyes. 14,42,43 Our analysis shows that a push−pull model can quantitatively describe the ring-opening reaction of rhodamines. The ring-opening reaction takes place between the lactone and zwitterion of 1.…”

“…The advent of super-resolution imaging and biomolecular labeling techniques (such as protein tags) demands the rapid development of high-performance organic fluorophores complementary to genetically encoded fluorescent proteins. − Among various organic fluorophores, oxygen/carbon/silicon-rhodamine dyes (henceforth denoted as rhodamines) represent one prolific class of fluorescent dyes. − Besides their excellent properties in brightness, photostability, and biocompatibility, rhodamines possess a unique ring-opening mechanism, via switching between their nonfluorescent lactone and fluorescent zwitterion/cation forms (Figure a) . This interesting switching process has enabled numerous bioimaging and biosensing applications and attracted substantial research interests. ,− However, molecular origins of the ring-opening mechanism in rhodamines remain largely unclear and rational design guidelines are still lacking to guide the systematic development of novel rhodamines with tailored fluorescent properties (such as for fluorogenic and super-resolution imaging applications).…”

Visualizing Material Processing via Photoexcitation-Controlled Organic-Phase Aggregation-Induced Emission

“…However, the difficulty to produce AIE in pure organic solvents by chemical or photochemical approaches could be the control of solubility difference between the reactant and the product. Instead, a photoexcitation-based physical process [34,35], which can sufficiently utilize photons to facilitate the entire molecular motion, could be a suitable approach to change the molecular solubility before and after irradiation. Thus far, several nonequilibrium systems based on the photoexcitation principle have been developed by overcoming the ultrafast relaxation and dissipation of the excitation state energy [36][37][38][39][40][41].…”

Boosting Circularly Polarized Luminescence of Organic Conjugated Systems via Twisted Intramolecular Charge Transfer

“…The dihedral angles of BINOL are completely dependent on the substituents. The electrondeficient o-carborane units are prone to induce molecular charge transfer, leading to a charge-separated state [23,24]. Twisted intramolecular charge transfer (TICT) emissions from o-1 to o-2 were observed, presumably originating from the rotational movement of o-carborane segments.…”