Lighting Up the Invisible Twisted Intramolecular Charge Transfer State by High Pressure

Abstract

The twisted intramolecular charge transfer (TICT) state plays an important role in determining the performance of optoelectronic devices. However, for some nonfluorescent TICT molecules, the "invisible" TICT state could only be visualized by modifying the molecular structure. Here, we introduce a new facile pressure-induced approach to light up the TICT state through the use of a pressurerelated liquid−solid phase transition of the surrounding solvent. Combining ultrafast spectroscopy and quantum chemical calculations, it reveals that the "invisible" TICT state can emit fluorescence when the rotation of a donor group is restricted by the frozen acetonitrile solution. Furthermore, the TICT process can even be effectively regulated by the external pressure. Our study offers a unique strategy to achieve dual fluorescence behavior in charge transfer molecules and is of significance for optoelectronic and biomedical applications.

A density functional theory‐time‐dependent density functional theory investigation of photo‐induced hydrogen bond and proton transfer for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐6‐carboxylicacid

“…Given the changes about bond angles, we find that the bond angles of O1H2⋯N3 and O4H5⋯O6 are 145.0° and 139.9° in the S0 state, which change to 147.9° and 141.8° in the S1 state. Thus, we can further confirm that the intramolecular hydrogen bonds O1H2⋯N3 should be strengthened in the first excited state . Worth noting is that the hydrogen bond H2⋯N3 demonstrates bigger changes than the H5⋯O6 bond; therefore, the excited‐state dynamical behavior of DDPBC may depend on the hydrogen bond O1H2⋯N3 to a great extent.…”

“…Therefore, it is difficult to judge the changes of the hydrogen bond O4H5⋯O6 only based on comparing geometrical parameters. Maybe the IR vibrational spectra could provide more definite results . Given the changes about bond angles, we find that the bond angles of O1H2⋯N3 and O4H5⋯O6 are 145.0° and 139.9° in the S0 state, which change to 147.9° and 141.8° in the S1 state.…”

“…As far as we know, the theoretical simulations of IR vibrational spectra are a better method to explore excited‐state intramolecular hydrogen‐bonding behaviors; therefore, we also perform the IR vibrational spectra calculations for the DDPBC system. As we mainly focus on the hydrogen‐bonding changes, we only show the IR stretching vibrational modes about O1H2 and O4H5 for DDPBC in Figure .…”

“…Obviously, the IR result of O1H2 is red‐shifted from 3278.3 cm −1 (S0) to 2794.3 cm −1 (S1), while that of O4H5 is red‐shifted from 3,698.8 cm −1 (S0) to 3,571.7 cm −1 (S1). The large redshift of intramolecular hydrogen bonds should be attributed to the strengthening phenomenon on photoexcitation . Comparing these two stretching modes (O1H2 and O4H5), we can say photo‐induced excitation plays a more significant role in the O1H2⋯N3 hydrogen bond.…”

“…According to the vertical excitation calculation results, we show the frontier molecular orbitals (MOs) of the DDPBC system, which could demonstrate the molecular characteristic and reaction tendency . Figure shows the frontier MOs of the DDPBC structure to depict the nature of electronic excited states.…”