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Issue 11, 2002
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Photophysical properties of [N]phenylenes

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In the present study, photophysical properties of [N]phenylenes were studied by means of stationary and time-resolved absorption and fluorescence spectroscopy (in THF at room temperature). For biphenylene (1) and linear [3]phenylene (2a), internal conversion (IC) with quantum yields ΦIC > 0.99 is by far the dominant mechanism of S1 state deactivation. Angular [3]phenylene (3a), the zig-zag [4]- and [5]phenylenes (3b), (3c), and the triangular [4]phenylene (4) show fluorescence emission with fluorescence quantum yields and lifetimes between ΦF = 0.07 for (3a) and 0.21 for (3c) and τF = 20 ns for (3a) and 81 ns for (4). Also, compounds (3) and (4) exhibit triplet formation upon photoexcitation with quantum yields as high as ΦISC = 0.45 for (3c). The strong differences in the fluorescence properties and in the triplet formation efficiencies between (1) and (2a) on one hand and (3) and (4) on the other are related to the remarkable variation of the internal conversion (IC) rate constants kIC. A tentative classification of (1) and (2a) as “fast IC compounds”, with kIC > 109 s−1, and of (3) and (4) as “slow IC compounds”, with kIC ≈ 107 s−1, is suggested. This classification cannot simply be related to Hückel's rule-type concepts of aromaticity, because the group of “fast IC compounds” consists of “antiaromatic” (1) and “aromatic” (2a), and the group of “slow IC compounds” consists of “antiaromatic” (3b), (4) and “aromatic” (3a), (3c). The IC in the [N]phenylenes is discussed within the framework of the so-called energy gap law established for non-radiative processes in benzenoid hydrocarbons.

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Article information

12 Oct 2001
04 Jan 2002
First published
30 Apr 2002

Phys. Chem. Chem. Phys., 2002,4, 2156-2161
Article type

Photophysical properties of [N]phenylenes

C. Dosche, H.-G. Löhmannsröben, A. Bieser, P. I. Dosa, S. Han, M. Iwamoto, A. Schleifenbaum and K. P. C. Vollhardt, Phys. Chem. Chem. Phys., 2002, 4, 2156
DOI: 10.1039/B109342H

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