The role of hydrogen bonding in excited state intramolecular charge transfer

Abstract

Intramolecular charge transfer (ICT) that occurs upon photoexcitation of molecules is a vital process in nature and it has ample applications in chemistry and biology. The ICT process of the excited molecules is affected by several environmental factors including polarity, viscosity and hydrogen bonding. The effect of polarity and viscosity on the ICT processes is well understood. But, despite the fact that hydrogen bonding significantly influences the ICT process, the specific role of hydrogen bonding in the formation and stabilization of the ICT state is not unambiguously established. Some literature reports predicted that the hydrogen bonding of the solvent with a donor promotes the formation of a twisted intramolecular charge transfer (TICT) state. Some other reports stated that it inhibits the formation of the TICT state. Alternatively, it was proposed that the hydrogen bonding of the solvent with an acceptor favors the TICT state. It is also observed that a dynamic equilibrium is established between the free and the hydrogen bonded ICT states. This perspective focuses on the specific role played by hydrogen bonding of the solvent with the donor and the acceptor, and by proton transfer in the ICT process. The utility of such influence in molecular recognition and anion sensing is discussed with a few recent literature examples in the end.

Relay proton transfer triggered twisted intramolecular charge transfer

“…According to TICT model, the twisting of donor to a perpendicular geometry is associated with intramolecular charge transfer process. [13][14][15][16][17][18][19][20] Solvents can form hydrogen bond with either the charge donor or the charge acceptor of the molecule. It is well documented that the TICT emission depends on the polarity as well as that of viscosity.…”

“…The charge localized on the dimethylamino group in the highest occupied molecular orbital (HOMO) and on the other part of the molecule in the lowest unoccupied molecular orbital (LUMO). The proton transfer induced charge transfer that lead to nonradiative process was reported in number of molecules 13,62. The proton transfer induced charge transfer that lead to nonradiative process was reported in number of molecules 13,62.…”

Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers

“…It was further proposed that intermolecular hydrogen-bonding of the carbonyl oxygen and/or the imide nitrogen with solvent molecules in protic solvents results in a drop of the quantum yield 26,29 accompanied by a pronounced red-shi of emission maxima. 21,23,31 Due to this strong environmental sensitivity, besides several reports regarding their use in chemosensors for detection of metal ions, 30,32,33 these uorophores were also exploited as a tool for monitoring protein-protein interactions, 27,34 or as a potential sensor for DNA. [35][36][37] Also, they have recently been used to signal the pH-induced conformational changes of a protein.…”

Bichromophoric Sensors for Ratiometric Measurements of Molecular Microenvironments through the Interplay of Charge Transfer and Energy Transfer Channels

“…The most important feature is that the CT state decay times in acetone (115 � 8 ps and 302 � 7 ps) are smaller than the ones measured in propanol (Table S6). If the electron donor section of the molecule forms hydrogen bonds with the solvent, these have to break after the electron transfer to the acceptor, due to the donor becoming positively charged [31] . If the electron donor section of the molecule forms hydrogen bonds with the solvent, these have to break after the electron transfer to the acceptor, due to the donor becoming positively charged [31] .…”