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Charge shift and triplet state formation in the 9-mesityl-10- methylacridinium cation

Lookup NU author(s): Professor Andrew Benniston, Emeritus Professor Anthony Harriman

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Abstract

The target donor-acceptor compound forms an acridinium-like, locally excited (LE) singlet state on illumination with blue or near-UV light. This LE state undergoes rapid charge transfer from the acridinium ion to the orthogonally sited mesityl group in polar solution. The resultant charge-transfer (CT) state fluoresces in modest yield and decays on the nanosecond time scale. The LE and CT states reside in thermal equilibrium at ambient temperature; decay of both states is weakly activated in fluid solution, but decay of the CT state is activationless in a glassy matrix. Analysis of the fluorescence spectrum allows precise location of the relevant energy levels. Intersystem crossing competes with radiative and nonradiative decay of the CT state such that an acridinium-like, locally excited triplet state is formed in both fluid solution and a glassy matrix. Phosphorescence spectra position the triplet energy well below that of the CT state. The triplet decays via first-order kinetics with a lifetime of ca. 30 αve;s at room temperature in the absence of oxygen but survives for ca. 5 ms in an ethanol glass at 77 K. The quantum yield for formation of the LE triplet state is 0.38 but increases by a factor of 2.3-fold in the presence of iodomethane. The triplet reacts with molecular oxygen to produce singlet molecular oxygen in high quantum yield. In sharp contradiction to a recent literature report, there is no spectroscopic evidence to indicate the presence of an unusually long-lived CT state. © 2005 American Chemical Society.


Publication metadata

Author(s): Benniston AC, Harriman A, Li P, Rostron JP, Van Ramesdonk HJ, Groeneveld MM, Zhang H, Verhoeven JW

Publication type: Article

Publication status: Published

Journal: Journal of the American Chemical Society

Year: 2005

Volume: 127

Issue: 46

Pages: 16054-16064

Print publication date: 23/11/2005

ISSN (print): 0002-7863

ISSN (electronic): 1520-5126

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ja052967e

DOI: 10.1021/ja052967e


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