title: Design of weak-donor alkyl-functionalized push-pull pyrene dyes exhibiting enhanced fluorescence quantum yields and unique on/off switching properties.
abstract: We designed, synthesized, and evaluated environmentally responsive solvatochromic fluorescent dyes by incorporating weak push-pull moieties. The quantum yields of the push (alkyl)-pull (formyl) pyrene dyes were dramatically enhanced by the introduction of alkyl groups into formylpyrene (1-formylpyrene: Φ(F) =0.10; 3,6,8-tri-n-butyl-1-formylpyrene: Φ(F) =0.90; in MeOH). The new dyes exhibited unique sensitivity to solvent polarity and hydrogen-bond donor ability, and specific fluorescence turn-on/off properties (e.g., 3,6,8-tri-n-butyl-1-formylpyrene: Φ(F) =0.004, 0.80, 0.37, and 0.90 in hexane, chloroform, DMSO, and MeOH, respectively). Here, the alkyl groups act as weak donors to suppress intersystem crossing by destabilizing the HOMOs of 1-formylpyrene while maintaining weak intramolecular charge-transfer properties. By using alkyl groups as weak donors, environmentally responsive, and in particular, pH-responsive fluorescent materials may be developed in the future.
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152-8552 (Japan), Fax: (+81) 3-5734-2321.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Niko
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Sasaki
authors.forename: Susumu
authors.initials: S
authors.lastname: Kawauchi
authors.forename: Katsumi
authors.initials: K
authors.lastname: Tokumaru
authors.forename: Gen-Ichi
authors.initials: G
authors.lastname: Konishi
keywords: charge transfer; donor-acceptor systems; dyes/pigments; fluorescence; solvatochromism