Charge-transfer state and large first hyperpolarizability constant in a highly electronically coupled zinc and gold porphyrin dyad.
We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense charge-transfer band localized at lambda = 739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP-ZnP and AuP-AuP) was undertaken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge-separated state ((+)ZnP-AuP(*)) that displays a particularly long lifetime (tau = 4 ns in toluene) for such a short separation distance. The molecular orbitals of the dyad were determined by DFT quantum-chemical calculations. This theoretical study confirms that the observed intense band at lambda = 739 nm corresponds to an interporphyrin charge-transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitals localized on the gold porphyrin. Finally, a Hyper-Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (beta = 2100x10(-30) esu at lambda = 1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push-pull porphyrin system.
Fortage
Jérôme
J
University of Nantes, CEISAM, Chimie et Interdisciplinarité, Synthèse, Analyse, Modélisation, Faculté des Sciences et des Techniques, 2, rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France.
Scarpaci
Annabelle
A
Viau
Lydie
L
Pellegrin
Yann
Y
Blart
Errol
E
Falkenström
Magnus
M
Hammarström
Leif
L
Asselberghs
Inge
I
Kellens
Ruben
R
Libaers
Wim
W
Clays
Koen
K
Eng
Mattias P
MP
Odobel
Fabrice
F