Abstract
In the recent literature a simple 9‐aryl‐acridinium ion was claimed to undergo an intramolecular, photoinduced charge shift to produce an extremely long‐lived and very high energy charge‐transfer state. The possible consequences of this observation are discussed and the tenability of the claims made is investigated via time resolved spectroscopy of a closely related system with spectroscopic characteristics allowing more solid identification of the actual photophysical events taking place. From the results obtained it appears likely that the long‐lived species observed earlier in solution cannot be charge transfer in nature but must instead be identified as the lowest triplet state of the acridinium chromophore.
Highlights
Storage of light energy in a long-lived molecular chargetransfer state is a much pursued goal. Such molecular systems would be of importance for energy conversion analogous to natural photosynthesis and might be applied in the construction of molecular photoelectromechanical and photo-electric devices
The most successful of such systems seem to be those in which “spin control” is applied by populating a chargetransfer state which is of different spin multiplicity than the ground state whereby charge recombination becomes a spin forbidden process [9,10,11,12]
After the laser pulse spectrum-1 is observed, with a maximum at 480 nm and a shoulder at ∼ 580 nm, which may be attributed to S1 → Sn absorption of the acridinium chromophore
Summary
Storage of light energy in a long-lived molecular chargetransfer state is a much pursued goal. Crucial in photosynthetic energy conversion is the occurrence of a number of relatively fast short-range electron-transfer steps leading to a large overall charge separation distance which prevents the loss of the photoinduced redox potential as a result of rapid back electron transfer. Mimicking this has been achieved after decades of scientific effort but requires quite complex and large multi-chromophoric systems ranging from triads to pentads [1,2,3,4,5,6,7,8]. While all earlier results indicated that creation of a long-lived charge-transfer (CT) state is a complex issue, a very simple and compact dyad was recently reported in which a long-lived CT state was claimed to be populated without the need for long distance
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