TY - JOUR
T1 - Electrochemical Switching of a Fluorescent Molecular Rotor Embedded within a Bistable Rotaxane
AU - Wu, Yilei
AU - Frasconi, Marco
AU - Liu, Wei Guang
AU - Young, Ryan M.
AU - Goddard, William A.
AU - Wasielewski, Michael R.
AU - Stoddart, J. Fraser
N1 - Funding Information:
The authors thank NU for their continued support of this research. Synthesis was supported by the National Science Foundation under CHE-1308107 (J.F.S.). This project was also supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DE-FG02-99ER14999 (M.R.W.). W.-G.L. and W.A.G. were supported by NSF (CBET-1805022). Y.W. thanks the Fulbright Scholar Program for a Fellowship and the NU International Institute of Nanotechnology for a Ryan Fellowship. We thank the personnel in the Integrated Molecular Structure Education and Research Center (IMSERC) at Northwestern University (NU) for their assistance in the collection of the analytical data.
Publisher Copyright:
© 2020 American Chemical Society.
PY - 2020/7/8
Y1 - 2020/7/8
N2 - We report how the nanoconfined environment, introduced by the mechanical bonds within an electrochemically switchable bistable [2]rotaxane, controls the rotation of a fluorescent molecular rotor, namely, an 8-phenyl-substituted boron dipyrromethene (BODIPY). The electrochemical switching of the bistable [2]rotaxane induces changes in the ground-state coconformation and in the corresponding excited-state properties of the BODIPY rotor. In the starting redox state, when no external potential is applied, the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles the tetrathiafulvalene (TTF) unit on the dumbbell component, leaving the BODIPY rotor unhindered and exhibiting low fluorescence. Upon oxidation of the TTF unit to a TTF2+ dication, the CBPQT4+ ring is forced toward the molecular rotor, leading to an increased energy barrier for the excited state to rotate the rotor into the state with a high nonradiative rate constant, resulting in an overall 3.4-fold fluorescence enhancement. On the other hand, when the solvent polarity is high enough to stabilize the excited charge-transfer state between the BODIPY rotor and the CBPQT4+ ring, movement of the ring toward the BODIPY rotor produces an unexpectedly strong fluorescence signal decrease as the result of photoinduced electron transfer from the BODIPY rotor to the CBPQT4+ ring. The nanoconfinement effect introduced by mechanical bonding can effectively lead to modulation of the physicochemical properties as observed in this bistable [2]rotaxane. On account of the straightforward synthetic strategy and the facile modulation of switchable electrochromic behavior, our approach could pave the way for the development of new stimuli-responsive materials based on mechanically interlocked molecules for future electro-optical applications, such as sensors, molecular memories, and molecular logic gates.
AB - We report how the nanoconfined environment, introduced by the mechanical bonds within an electrochemically switchable bistable [2]rotaxane, controls the rotation of a fluorescent molecular rotor, namely, an 8-phenyl-substituted boron dipyrromethene (BODIPY). The electrochemical switching of the bistable [2]rotaxane induces changes in the ground-state coconformation and in the corresponding excited-state properties of the BODIPY rotor. In the starting redox state, when no external potential is applied, the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles the tetrathiafulvalene (TTF) unit on the dumbbell component, leaving the BODIPY rotor unhindered and exhibiting low fluorescence. Upon oxidation of the TTF unit to a TTF2+ dication, the CBPQT4+ ring is forced toward the molecular rotor, leading to an increased energy barrier for the excited state to rotate the rotor into the state with a high nonradiative rate constant, resulting in an overall 3.4-fold fluorescence enhancement. On the other hand, when the solvent polarity is high enough to stabilize the excited charge-transfer state between the BODIPY rotor and the CBPQT4+ ring, movement of the ring toward the BODIPY rotor produces an unexpectedly strong fluorescence signal decrease as the result of photoinduced electron transfer from the BODIPY rotor to the CBPQT4+ ring. The nanoconfinement effect introduced by mechanical bonding can effectively lead to modulation of the physicochemical properties as observed in this bistable [2]rotaxane. On account of the straightforward synthetic strategy and the facile modulation of switchable electrochromic behavior, our approach could pave the way for the development of new stimuli-responsive materials based on mechanically interlocked molecules for future electro-optical applications, such as sensors, molecular memories, and molecular logic gates.
UR - http://www.scopus.com/inward/record.url?scp=85087673866&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85087673866&partnerID=8YFLogxK
U2 - 10.1021/jacs.0c03701
DO - 10.1021/jacs.0c03701
M3 - Article
C2 - 32470290
AN - SCOPUS:85087673866
VL - 142
SP - 11835
EP - 11846
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 27
ER -