Transient absorption spectroscopy is an effective method for characterizing excited states of molecules. Also called laser flash photolysis or pump-probe experiments, transient absorption relies on quickly populating the excited state followed by probing the excited state. In order to obtain an “instantaneous” population of excited states within a sample, a laser source is generally used. Detection of the excited state is commonly performed by a xenon lamp. Measurements are recorded by a PMT or CCD camera detector connected to a personal computer. Additionally, time-resolved measurements are possible, allowing for kinetic data of the excited states to be obtained.

Charge and Exciton Migration

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 (Figure 2). The triplet-triplet energy transfer within molecular aggregates consisting of phosphorescent platinum-acetylide oligomers is shown in the emission spectroscopy (Figure 3).

Figure 1. Pt-acetylide oligomers                                       Figure 2. Representative TEM image
Figure 3. Emission of Pt-acetylide oligomers