title: Acid/base-triggered switching of circularly polarized luminescence and electronic circular dichroism in organic and organometallic helicenes.
abstract: Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene-bipyridine proligand 1 a and in its "rollover" cycloplatinated derivative 2 a. Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum-chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene-bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge-transfer-type transition rather than a π-π* transition) as well as an increase in the HOMO-LUMO character of the transition and stabilization of the LUMO level upon protonation.
authors.affiliation: Institut des Sciences Chimiques de Rennes, UMR 6226, Institut de Physique de Rennes, UMR 6251, Campus de Beaulieu, CNRS-Université de Rennes 1, 35042 Rennes Cedex (France).
authors.forename: Nidal
authors.initials: N
authors.lastname: Saleh
authors.forename: Barry
authors.initials: B
authors.lastname: Moore
authors.forename: Monika
authors.initials: M
authors.lastname: Srebro
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vanthuyne
authors.forename: Loïc
authors.initials: L
authors.lastname: Toupet
authors.forename: J A Gareth
authors.initials: JA
authors.lastname: Williams
authors.forename: Christian
authors.initials: C
authors.lastname: Roussel
authors.forename: Kirandeep K
authors.initials: KK
authors.lastname: Deol
authors.forename: Gilles
authors.initials: G
authors.lastname: Muller
authors.forename: Jochen
authors.initials: J
authors.lastname: Autschbach
authors.forename: Jeanne
authors.initials: J
authors.lastname: Crassous
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry; D000143:Acids / Q000737:chemistry; D002942:Circular Dichroism; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D049449:Luminescence; D008163:Luminescent Measurements; D008958:Models, Molecular; D009944:Organoplatinum Compounds / Q000737:chemistry*; D011083:Polycyclic Compounds / Q000737:chemistry*
chemical_list: D000143:Acids; D009944:Organoplatinum Compounds; D011083:Polycyclic Compounds; C031660:helicenes; D015082:2,2'-Dipyridyl
keywords: circular dichroism; density functional calculations; helicenes; luminescence; switches