The synthesis and spectroscopic properties of organometallic cyanine analogues

Abstract

Organometallic compounds are receiving attention as potential second-order and third-order nonlinear optical (NLO) materials.[' -71 Experimental and theoretical studies on hyperpolarizabilities indicate that molecules with large transition dipole moments and small energy gaps are, in general, likely candidates for NLO materials.[*] Thus, as part of our on going program to develop new chromophores, we sought to design organometallic compounds with these properties. Many organometallic complexes exhibit metal to ligand charge transfer (MLCT) bands. However, these bands often exhibit only moderate extinction coefficients in the range of 1000 -20000 M -cm-' which may be limited by relatively weak coupling between the metal and the ligand."' We believe organometallic compounds could be useful in nonlinear optics[*] if the electronic coupling between the transition metal and the organic fragment can be optimized, thereby resulting in stronger optical transitions.

Synthesis and linear and nonlinear optical properties of metal-terminated bis(dioxaborine) polymethines

“…We chose to attach cyclometallated Rh and Ir species to this ligand due to their well-established chemistry, as well as their synthetic flexibility, which we anticipated would enable us to obtain final products that would be processible into thin films. It is worth noting that although several polymethines have been reported in which the primary charge-stabilising end groups are organometallic fragments, such as [RuCl(dppe)(PPh 3 )(CO)] or [Cp 2 Fe 2 (CO) 3 C], 14,15 we are unaware of any examples in which transition-metal moieties have been used to modify polymethine properties through coordination to post-terminal groups. The synthesis of 1a-c is shown in Scheme 1 (see ESIw for details).…”