title: Excited state dynamics and structures of functionalized phthalocyanines. 1. Self-regulated assembly of zinc helicenocyanine.
abstract: Recently synthesized zinc helicenocyanine (ZnHc), where four helicene groups are fused with a phthalocyanine (Pc) core through all-carbon linkages, exhibits an unusually strong tendency of forming soluble molecular aggregates in organic solvents. The aggregation results in a strong optical absorption across most of the visible region, which is drastically different from that of its monomer. The aggregation is suppressed by dissolving ZnHc in a liquid crystal, octylbiphenylcarbonitrile (OBCN), where the monomer ZnHc dominates and exhibits a typical optical absorption spectrum of monomeric zinc phthalocyanine, except red shift in both Q- and B- bands due to pi-conjugation expansion. This study correlates optical properties and excited state dynamics of ZnHc with intra- and intermolecular electronic interactions, using quantum mechanical calculations and ultrafast transient absorption spectroscopy. Structural details of the aggregates are revealed by small-angle X-ray scattering (SAXS) to be uniformly dimers with alkoxy chains wrapped around the core of a face-to-face dimer. The results suggest that while the peripheral helicene moieties in ZnHc are electronically coupled to the Pc core via expansion of the pi-conjugation of the macrocycle, the coupling is attenuated by the "lock washer" conformation of the nonplanar peripheral helicenes which prevents pi-conjugation throughout the entire macrocycle. The interplay between pi-conjugation expansion in the macrocyle plane and the pi-pi stacking out of the macrocyle plane produces a structure that facilitates the unique optical properties and self-regulated assembly into nanoscale structures in solution. These novel optical properties are explored for potential applications in various areas.
authors.affiliation: Chemistry Division and Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Lin X
authors.initials: LX
authors.lastname: Chen
authors.forename: George B
authors.initials: GB
authors.lastname: Shaw
authors.forename: David M
authors.initials: DM
authors.lastname: Tiede
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Zuo
authors.forename: Peter
authors.initials: P
authors.lastname: Zapol
authors.forename: Paul C
authors.initials: PC
authors.lastname: Redfern
authors.forename: Larry A
authors.initials: LA
authors.lastname: Curtiss
authors.forename: Thanasat
authors.initials: T
authors.lastname: Sooksimuang
authors.forename: Braja K
authors.initials: BK
authors.lastname: Mandal
mesh_terms: D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D007700:Kinetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D012542:Scattering, Radiation; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D007211:Indoles; D054833:Isoindoles; D009942:Organometallic Compounds; C520660:zinc tetrakis-beta-4,9,19,24,34,39,49,54-octadodecyloxyhelicenocyanine; C013647:phthalocyanine