Article

Long-Lived, Mobile Charge Carriers Formed on Photoexcitation of UV-Polymerized, Spin-Coated Films of Arylimido−Spacer−Diacetylene Derivatives

Radiation Chemistry Department, IRI, Delft University of Technology, Mekelweg 15, 2629 JB, Delft, The Netherlands
Laboratory of Organic Chemistry, Department of Biomolecular Sciences, Wageningen University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands
Macromolecules, 2000, 33 (1), pp 60–66
DOI: 10.1021/ma9904870
Publication Date (Web): December 17, 1999
Copyright © 2000 American Chemical Society

Abstract

The photopolymerization of spin-coated films of diacetylene derivatives containing phthalimido or naphthaldiimido moieties has been studied by monitoring the increase in the optical absorption in the visible region on irradiation at 308 nm. The phthalimido derivatives form blue polymers with absorption maxima at ca. 630 nm, corresponding to a highly conjugated, close to planar polydiacetylene (PDA) backbone configuration. The naphthaldiimido derivative yields a red polymer with an absorption maximum at 535 nm, indicating a backbone structure with a substantially reduced degree of π-bond conjugation. The initial, “low-dose” quantum yields for monomer conversion, based on the total number of photons absorbed at 308 nm, range from 2 to 20. Monomer conversions up to ca. 50% are found. The polymerized films are found to be photoconductive using the time-resolved microwave conductivity technique (TRMC). Mobile charge carriers are suggested to be formed via the triplet state of the arylimido moieties which undergoes long-distance charge transfer to polydiacetylene chains to form the arylimido radical anion and the mobile PDA radical cation or “hole”. A maximum value of 1.4 × 10-2 cm2/(V s) for the product of the quantum yield for charge carrier formation and the hole mobility is found. The photoconductivity of the “blue” polymer is approximately an order of magnitude larger than for the “red” variety. This is attributed to a higher mobility of PDA holes in the former compound, resulting from the higher degree of backbone conjugation. The lifetime of the mobile carriers extends well into the microsecond region, which is considerably longer than previously found on direct ionization of PDA chains.

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Article Views: 239 Times
Received 2 April 1999
Published online 17 December 1999
Published in print 1 January 2000
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