Organometallic Conjugated Molecules and Materials

π-conjugated molecules and polymers have been of wide interest for several decades.  This family of chromophores exhibits broad and tunable light absorption and luminescence throughout the visible and near-infrared range.  The materials have been of interest for fundamental reasons, but also for their use in organic optoelectronic devices such as organic light emitting diodes and organic/polymer solar cells.  Our group has a special interest in exploring the effect of heavy metals such as platinum(II) and iridium(III) on the optical properties of pi-conjugated molecules and chromophores.  Heavy metals can interact with a pi-conjugated electronic system, introducing mixing of different electron spin states (singlet – triplet mixing).  This effect can induce interesting optical phenomena, such as the existence of strong phosphorescence, non-linear optical properties for laser protection systems, and long lived excitons that can be beneficial in solar cell applications.  In this area of investigation, our group conducts synthetic organic and organometallic molecular and polymer synthesis to make materials that may exhibit interesting or unusual optical properties.  We the apply optical methods to study the materials and utilize them in applications such as high efficiency organic light emitting diodes and organic (polymer) solar cells.


CHARGE AND EXCITON MIGRATION

OMchromophore

We are investigating the excited state properties (absorption, luminescence, etc.) of p-conjugated oligomers and polymers that incorporate transition metals such as Ru, Pt, and Ir, as we are interested in understanding the effect of the heavy metal on the properties of the conjugated systems. We have applied many different photophysical studies toward understanding the properties of these novel materials, including steady state emission, time-resolved emission, and transient absorption techniques. Synthetic organic chemistry is a necessary prerequisite in determining the structure-property relationships of these organometallic and metal-organic materials.

One current project involves the synthesis of a series of monodisperse organometallic oligomers endcapped with easily-reducible moieties. The conjugated material (core) has been shown to act as a “molecular wire” in which both charge and energy can easily migrate along the conjugated backbone, until trapped as charge at a lower energy site (endcap). The main objective of this work is to investigate the dynamics of both charge and energy transport in these materials. Collaborations with other institutions involve the use of pulse radiolytic and femtosecond transient absorption techniques to better understand migration dynamics.


AGGREGATION AND GELATION

We study the properties of aggregates or gels consisting of metal-organic or organometallic-conjugated oligomers or polymers. The primary objective of this project is to design metal-containing molecular arrays that self-assemble in solution and to study the triplet exciton migration on these aggregates. Figure 1 shows a few examples of Platinum-acetylide oligomers which aggregate or gel in hydrocarbon solvents. The molecules stack to form a ordered fibrous network as shown in the TEM images. Phosphorescent platinum-acetylide oligomers display triplet-triplet energy transfer within the molecular aggregates consists.

Figure 1. Representative TEM image