Design of Weak-Donor Alkyl-Functionalized Push-Pull Pyrene Dyes Exhibiting Enhanced Fluorescence Quantum Yields and Unique On/Off Switching Properties

• Published in: Chemistry, an Asian journal an Asian journal, 2014-07, Vol.9 (7), p.1797-1807
• Main Authors: Niko, Yosuke, Sasaki, Shunsuke, Kawauchi, Susumu, Tokumaru, Katsumi, Konishi, Gen-ichi
• Format: Article
• Language: English
• Subjects: charge transfer; Chemistry; donor-acceptor systems; Dyes; dyes/pigments; fluorescence; solvatochromism
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201402088

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: ΦF=0.10; 3,6,8‐tri‐n‐butyl‐1‐formylpyrene: ΦF=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: ΦF=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. A little pushy: Alkyl push–pull pyrene dyes functionalized by alkyl (donor) groups exhibit unique sensitivity to solvent polarity, hydrogen‐bond donor ability, and specific fluorescence on/off switching properties (the figure shows data for 3,6,8‐n‐butyl‐1‐formylpyrene).