Liquid Crystals

Metallomesogens based on d-block metals are extremely complex dynamic materials, proposed as good candidates in luminescent applications due to the combination of excellent photophysical properties with properties deriving from liquid crystals (self-healing, order and mobility). However, important limitations consisting in strong luminescence extinction via non-radiative de-exciting paths (favoured by molecular aggregation) or presence of poisonous groups that compromise the stability of optoelectronic devices limited their applicability. Their complexity makes difficult the direct correlation of structure-properties relationship with respect to other condensed systems, thus complicating their optimisation by molecular engineering. However, the possibility of achieving a theoretically unitary luminescence yield, to favour luminescence enhancement through excimer formation in mesophase and the possibility of tuning the photophysical properties of the metallomesogens, make these an interesting subject of investigation both from an academic and industrial point of view. The importance of structural investigations in condensed phases linked with complete photophysical investigations (absorption and emission maxima, quantum yields, lifetimes of excited states) in solution, crystalline/amorphous powdered solid states and liquid crystalline mesophases at different temperatures is highlighted. The authors gathered in this chapter some representative examples of luminescent coordination complexes with d6, d8 and d10 metals reported in the literature, as a foundation on which further developments can be judiciously build.