Transient absorption (TA) measurements on nanosecond through microsecond time scales were performed on solutions of tris(2,2'-bipyridine)ruthenium(II) and anthracene in various relative concentrations. Following energy transfer from the ruthenium trisbipyridine sensitizer, the anthracene acceptor undergoes dimerization, which has been shown to occur via triplet-triplet annihilation. Values of the associated rate constants were determined by fitting the experimental TA data to the nonlinear kinetic model implied by the law of mass action. We report values of 6.9 × 108 liter mol−1 s−1 and 7.9 × 109 liter mol−1 s−1, respectively, for the rate constants for energy transfer and for anthracene dimerization.
Here, we present our development of several experimental methods, which, when applied together, can provide a thorough characterization of the nonlinear refraction and absorption properties of materials. We focus mainly on time-resolved methods for studying both transient absorption and refraction that reveal molecular dynamics including excited-state absorption, singlet-triplet transfer, instantaneous electronic nonlinear refraction, and molecular reorientation. In particular, we will describe our recent studies of new materials including organometallic compounds and organic solvents such as Tetrachloroethylene (C2Cl4).
The chemical and photophysical properties of metal dithiolene compounds have been studied since the 1960’s due to the noninnocent nature of the dithiolene ligands and their rich, reversible electrochemistry. This class of materials have been utilized as biomimetic catalysts, sensitizers for solar energy conversion, laser dyes, and non-linear optical materials thanks in part due to their large photostability. We synthesized a series of nickel (II) and gold (III) dithiolenes with different functional groups in the para positions of the benzene rings to study the structure-property relationships in comparison to those that are commercially available. We will present spectroelectrochemistry data, femtosecond transient difference absorption spectra, and Z-scans in an effort to quantify the ground and excited-state photophysical properties of these compounds.
Organometallic iridium(III) complexes have seen widespread use over the past two decades, particularly as phosphorescent dopants in organic light emitting diodes (OLEDs) due to their large spin-orbit coupling and metal-toligand charge transfer (MLCT) excited states. Interest in the non-linear optical (NLO) applications of these materials has increased recently with reports of both two-photon absorption (2PA) and reverse saturable absorption (RSA). A family of materials of the form [IrIII(NO2piq)2(acac)] were synthesized and characterized, where acac is acetylacetonate and NO2piq is a nitrophenylisoquinoline ligand. In order to assess structure-property relationships for the photophysics of these complexes, the placement of the nitro group was altered on the phenyl ring. Systematic control over the maxima of the absorption and photoluminescence bands attributed to the MLCT excited states was achieved through the ligand variation. The photophysical properties of this family of materials are discussed in detail and include their linear absorption spectra, photoluminescence measurements at 298 and 77K, excited state lifetimes, and CIE color chromaticity coordinates.
The photophysical properties of cyclometallated iridium compounds are beneficial for nonlinear optical (NLO) applications, such as the design of reverse saturable absorption (RSA) materials. We report on the NLO characterization of a family of compounds of the form [Ir(pbt)2(LX)], where pbt is 2-phenylbenzothiazole and LX is a beta-diketonate ligand. In particular, we investigate the effects of trifluoromethylation on compound solubility and photophysics compared to the parent acetylacetonate (acac) version. The NLO properties, such as the singlet and triplet excited-state cross sections, of these compounds were measured using the Z-scan technique. The excited-state lifetimes were determined from visible transient absorption spectroscopy.