Synthesis, non-linear optical and electrochemical properties of novel organoimido polyoxometalate derivatives

This thesis concerns the design and synthesis of a new class of earth abundant redox-active, hybrid inorganic-organic chromophores for use in second-order non-linear optics (NLO): organoimido polyoxometalates (POMs). It presents the first experimental measurements of 2nd order NLO (frequency doubling) coefficients (β) (by hyper-Rayleigh scattering, HRS) and the first spectroelectrochemical measurements on such species. Towards the aim of producing practical miniaturized devices, the species characterised include systems functionalised with pyrrole and carbazole donors that can be electropolymerized to form potentially redox switchable, photoactive films. These are the first reported POM-containing electropolymers with a covalently attached POM, and indicate the potential of these materials for straightforward electrodeposition onto optically transparent, conductive surfaces. To investigate the structure-activity relationships of the β response, the series of organoimido-Lindqvist chromophores included organic groups with different electron donors (such as amino, dimethylamino, and diphenylamino functionalities), or acceptors (such as iodo, and nitro), and different π -conjugated bridges. Significant β-values were obtained for derivatives with resonance electron donors, and result from strong ligand-to-polyoxometalate charge transfer transitions. No activity was observed for derivatives with resonance electron acceptors, indicating that the POM can only behave as an acceptor. β values increase steadily as the donor strength increases, and/or the π-conjugation extends, in similar fashion to organic systems. Interestingly, the highest β0-values obtained these derivatives exceed those of any dipolar organic system with comparable donor, π-system and absorption profile, and thus they have much more favourable transparency/non-linearity trade-offs. Resonance Raman and Stark spectroscopy results have confirmed involvement of the POM in the charge transfer transition, which results in unusual dipole moment changes leading to high NLO activity based on the two state model.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2016

Author dc:creator

• Al-Yasari, Ahmed

Language dc:language

en