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Synthetic control over intra- and intermolecular charge transfer can turn on the fluorescence emission of non-emissive coumarin

Title
Synthetic control over intra- and intermolecular charge transfer can turn on the fluorescence emission of non-emissive coumarin
Authors
Jhun, Byung HakOhkubo, KeiFukuzumi, ShunichiYou, Youngmin
Ewha Authors
유영민Shunichi FukuzumiKei Okubo
SCOPUS Author ID
유영민scopus; Shunichi Fukuzumiscopus; Kei Okuboscopus
Issue Date
2016
Journal Title
JOURNAL OF MATERIALS CHEMISTRY C
ISSN
2050-7526JCR Link2050-7534JCR Link
Citation
vol. 4, no. 20, pp. 4556 - 4567
Publisher
ROYAL SOC CHEMISTRY
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
Conjugated molecules bearing carbonyl groups typically exhibit weak fluorescence emission due to the presence of a non-radiative n-pi* transition state. Strong fluorescence emission from n-pi* chromophores has been sought through the use of synthetic approaches that incorporate strong electron donors, such as amines, into the conjugated structures. As an alternative to these existing approaches, we investigated two charge-transfer strategies using a series of 1-benzopyran-2-one (coumarin) derivatives. The first strategy involved attaching chromophoric aryl moieties at the 7 position of coumarin. This molecular control produced two effects: the n-pi* transition state was destabilized and an intramolecular charge-transfer (ICT) state was generated. The photoluminescence quantum yields (PLQYs) of the bichromophoric dyads increased with the pi-conjugation length of the aryl groups, and a PLQY as high as 0.80 was achieved. The second strategy facilitated exciplex fluorescence in poly(N-vinylcarbazole) (PVK) films within which coumarin derivatives have been molecularly dispersed. A thermodynamic analysis based on electrochemical data indicated that exciplex generation involved electron transfer from PVK to photoexcited coumarin molecules. Exciplex fluorescence was uniquely advantageous in its ability to tune the fluorescence emission color upon addition of electron donors having oxidation potentials less positive than that of PVK. Mechanistic studies, including femtosecond laser flash photolysis, were conducted to identify the molecular parameters that governed the two fluorescence properties. A mechanistic understanding may provide useful insights into the development of electrofluorescent materials that harness triplet as well as singlet excitons.
DOI
10.1039/c6tc00639f
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엘텍공과대학 > 화학신소재공학전공 > Journal papers
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