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Synthetic Metals, Volume 153, Issues 1-3, 21 September 2005, Pages 289-292. doi:10.1016/j.synthmet.2005.07.149 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TY7-4H2F7HY-2P&_user=2322584&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000056897&_version=1&_urlVersion=0&_userid=2322584&md5=2740d6443c541756a8f59e19906f55e6

Abstract

A series of π conjugated oligomers were studied by absorption and photoluminescence spectroscopy. A linear relationship between the positioning of the absorption and photoluminescence maxima plotted against inverse conjugation length is observed. The relationships are in good agreement with the simple particle in a box method, one of the earliest descriptions of the properties of one-dimensional organic molecules. In addition to the electronic transition energies, it was observed that the Stokes shift also exhibited a well-defined relationship with increasing conjugation length, implying a correlation between the electron-vibrational coupling and chain length. This correlation is further examined using Raman spectroscopy, whereby the integrated Raman scattering is seen to behave superlinearly with chain length. There is a clear indication that the vibrational activity and thus nonradiative decay processes are controllable through molecular structure. The correlations between the Stokes energies and the vibrational structure are also observed in a selection of PPV based polymers and a clear trend of increasing luminescence efficiency with decreasing vibrational activity and Stokes shift is observable. The implications of such structure property relationships in terms of materials design are discussed.

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