Abstract
In this paper the results of dynamic NMR studies on ethylmethylamino-tertiary-butyl-phenylborane (EMABPB) with or without light are reported. The NMR data were recorded on a Bruker 400 MHz NMR equipped with our custom-made optical probe and with our custom-made 450 watts (W) monochromatic light sources. The molecular photochemistry including twisted intramolecular charge-transfer-excited-state (TICT) of the EMABPB in several solvents has been investigated. These results indicate that the aminoborane demonstrates multiple configurations in CD3Cl and CD2Cl2 resulting in the shifts of the signals of the alkyl groups on the nitrogen and boron. This indicates that there are some time-dependent changes at constant temperature over the irradiation interval. At ﹣60°C and the presence of light (λ = 265 nm), we observed a large change in the populations of the two sites, and this by itself indicates a modification in the rotation around the boron nitrogen bond in the excited state. By considering the existence of the TICT state, many important energy technologies may be developed with higher efficiency by controlling the back-electron transfer processes.
Highlights
Dual fluorescence phenomenon of 4-N,N-dimethylaminobenzonitrile (DMABN) and some other compounds in polar solvents have been studied by different scientists over the past several decades [1]-[4]
The more convincing theory was characterized by the existence of the highly polar emitting states in which the two donor and acceptor subsystems were mutually twisted by 90 ̊. These excited states received a name of Twisted-Intramolecular-Charge-Transfer-Excited States (TICT)
As we observed in the NMR spectra 3 - 7, aminoborane was the best candidate because the ΔG** of activation for the rotation around the B-N bond was high enough to clearly see separate signals for each alkyl group on boron and nitrogen for the two sites at room temperature
Summary
Dual fluorescence phenomenon of 4-N,N-dimethylaminobenzonitrile (DMABN) and some other compounds in polar solvents have been studied by different scientists over the past several decades [1]-[4]. The more convincing theory was characterized by the existence of the highly polar emitting states in which the two donor and acceptor subsystems were mutually twisted by 90 ̊. These excited states received a name of Twisted-Intramolecular-Charge-Transfer-Excited States (TICT). If this rotation really happens, after the electron transfer from donor to acceptor, the two excited wave functions will be orthogonal to one another. The back electron transfer will be slower This phenomenon can be used to considerably raise the efficiency of a solar cell, solar hydrogen and other types of solar energy storage and conversion
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