Structural and spectroscopic study of 6,7-dicyano-substituted lumazine with high electron affinity and proton acidity

Ken Ichi Sakai, Kenta Nagahara, Yuuya Yoshii, Norihisa Hoshino, Tomoyuki Akutagawa

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)

Abstract

The introduction of cyano groups into lumazine (pteridine-2,4-(1H,3H)dione) at the C6 and C7 positions enhances its electron affinity, proton acidity, and solubility in solvents. As a result, 6,7-dicyanolumazine (DCNLH2) forms charge transfer (CT) complexes with donors such as tetrathiafulvalene, 2,3,5,6-tetramethyl-1,4-phenylenediamine, and 3,3′,5,5′- tetramethylbenzidine and readily dissociates a proton from the N1 nitrogen to form a monoanionic salt with tetrabutylammonium (TBA+). Crystal structures of the CT complexes consist of mixed stacks in which DCNLH 2 interacts with donors in face-to-face configurations, but they form intermolecular hydrogen bonds differently depending on the donor type. In the TBA+ salt, two deprotonated DCNLH- monoanions form a unique dianionic dimer connected by two centrosymmetric hydrogen bonds, N3-H···O-C2, which is electronically isolated by the presence of bulky TBA+ countercations and the absence of a proton at the N1 hydrogen-bonding site. This dimer fluoresces yellowish green (fluorescence quantum yield Φ = 0.04). Because the DCNLH- anion only shows weak blue fluorescence in aqueous solution (Φ < 0.01), we suggest that the dimer formation is responsible for the fluorescence enhancement with a large emission band shift to the low-energy side.

Original languageEnglish
Pages (from-to)3614-3624
Number of pages11
JournalJournal of Physical Chemistry A
Volume117
Issue number17
DOIs
Publication statusPublished - 2013 May 2

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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