title: Luminescent Quadrupolar Borazine Oligomers: Synthesis, Photophysics, and Two-Photon Absorption Properties.
abstract: A set of monodisperse bent donor-acceptor-donor-type conjugated borazine oligomers, BnNn+1 (n=1-4), incorporating electron-rich triarylamine donor and electron-deficient triarylborane acceptor units has been prepared through an iterative synthetic approach that takes advantage of highly selective silicon-boron and tin-boron exchange reactions. The effect of chain elongation on the electrochemical, one- and two-photon properties and excited-state photodynamics has been investigated. Strong intramolecular charge transfer (ICT) from the arylamine donors to boryl-centered acceptor sites results in emissions with high quantum yields (Φfl >0.5) in the range of 400-500 nm. Solvatochromic effects lead to solvent shifts as large as ∼70 nm for the shortest member (n=1) and gradually decrease with chain elongation. The oligomers exhibit strong two-photon absorption (2PA) in the visible spectral region with 2PA cross sections as large as 1410 GM (n=4), and broadband excited-state absorption (ESA) attributed to long-lived singlet-singlet and radical cation/anion absorption. The excited-state dynamics also show sensitivity to the solvent environment. Electrochemical observations and DFT calculations (B3LYP/6-31G*) reveal spatially separated HOMO and LUMO levels resulting in highly fluorescent oligomers with strong ICT character. The BnNn+1 oligomers have been used to demonstrate the detection of cyanide anions with association constants of log K>7.
authors.affiliation: Department of Chemistry, Rutgers University Newark, Newark, NJ, 07102 (USA).
authors.forename: Pangkuan
authors.initials: P
authors.lastname: Chen
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, 30332-0400 (USA).
authors.forename: Ariel S
authors.initials: AS
authors.lastname: Marshall
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, 30332-0400 (USA).
authors.forename: San-Hui
authors.initials: SH
authors.lastname: Chi
authors.affiliation: Department of Chemistry, Rutgers University Newark, Newark, NJ, 07102 (USA).
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Yin
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, 30332-0400 (USA). joe.perry@chemistry.gatech.edu.
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Perry
authors.affiliation: Department of Chemistry, Rutgers University Newark, Newark, NJ, 07102 (USA). fjaekle@rutgers.edu.
authors.forename: Frieder
authors.initials: F
authors.lastname: Jäkle
keywords: borane; conjugation; donor-acceptor; fluorescence; two-photon absorption