Stark spectroscopy has been applied to a wide range of molecular systems and materials. A generally useful method for obtaining electronic and vibrational Stark spectra that does not require sophisticated equipment is described. By working with frozen glasses it is possible to study nearly any molecular system, including ions and proteins. Quantitative analysis of the spectra provides information on the change in dipole moment and polarizability associated with a transition. The change in dipole moment reflects the degree of charge separation for a transition, a quantity of interest to a variety of fields. The polarizability change describes the sensitivity of a transition to an electrostatic field such as that found in a protein or an ordered synthetic material. Applications to donor-acceptor polyenes, transition metal complexes (metal-to-ligand and metal-to-metal mixed valence transitions), and nonphotosynthetic biological systems are reviewed.

STARK SPECTROSCOPY: Applications in Chemistry, Biology, and Materials Science

Unusually large electric field effects have been measured for the absorption spectra of carotenoids (spheroidene) in the B800-850 light-harvesting complex from the photosynthetic bacterium Rhodobacter sphaeroides. Quantitative analysis shows that the difference in the permanent dipole moment between the ground state and excited states in this protein complex is substantially larger than for pure spheroidene extracted from the protein. The results demonstrate the presence of a large perturbation on the electronic structure of this nearly symmetric carotenoid due to the organized environment in the protein. This work also provides an explanation for the seemingly anomalous dependence of carotenoid band shifts on transmembrane potential and a generally useful approach for calibrating electric field-sensitive dyes that are widely used to probe potentials in biological systems.

https://science.sciencemag.org/content/sci/251/4994/662.full.pdf

Large protein-induced dipoles for a symmetric carotenoid in a photosynthetic antenna complex

Stark effect (electroabsorption) spectroscopy of photosynthetic reaction centers at 1.5K: Evidence that the special pair has a large excited-state polarizability

Perfluoroalkanes (PFs) have been shown to be unique solvents in spectral, photophysical and photochemical studies in fluid solutions. Their physical, chemical and spectral properties are discussed. Substantial differences between PFs and alkanes and similarities between PFs and the rare gases argon and krypton are illustrated. Examples are presented which illustrate the advantages of the use of PF solvents in the study of the contribution of non-specific and specific solute—solvent interactions to the experimentally observed spectral shift, in the determination of the role of intermolecular and intramolecular interactions for molecules of rigid and flexible structure, and in measurements of the energies and lifetimes of electronically excited states. The application of PF solvents in photophysical and photochemical studies, especially in the quantitative determination of the contribution of intramolecular and intermolecular processes to the decay paths of electronically excited molecules, is discussed. The results presented demonstrate that PFs considerably extend the polarity scale available for weakly interacting solvents. Therefore they are recommended as solvents in the investigation of the intramolecular properties of reactive molecules in electronically excited states. Some comments on the practical application of PFs are given and some studies using PFs are proposed.

The application of perfluoroalkanes as solvents in spectral, photophysical and photochemical studies

Using Stark effect (electroabsorption) spectroscopy to study the well-known solvatochromic probe molecule coumarin 153 (C153) in a variety of polymer matrices and organic glasses, we have found that the average change in polarizability ( ) that we measure depends critically on the rigidity of the matrix used. In rigid polymer and frozen organic glass matrices, the measured values are between 4 and 60 A3. The smaller values in this range are similar to those obtained via semiempirical and ab initio calculations. In contrast, measurements made on polymer matrices that are above their glass-transition temperature or those containing trapped solvent are more than an order of magnitude higher. We postulate that large values of result from field-induced orientation of the C153 molecule and/or the dipoles of the surrounding matrix in matrices that are not fully rigid. The absolute value of the change in dipole moment between the ground and excited states (|Δμ|) of C153 measured here ranges from 4.4 to 7.0 D, dep...

/pdf/effects-of-matrix-temperature-and-rigidity-on-the-electronic-49gthgxic1.pdf

Effects of Matrix Temperature and Rigidity on the Electronic Properties of Solvatochromic Molecules: Electroabsorption of Coumarin 153

Excited state dipole moments and polarizabilities of centrosymmetric and dimeric molecules. II. Polyenes, polyynes and cumulenes

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Excited state dipole moments and polarizabilities of centrosymmetric and dimeric molecules. II. Polyenes, polyynes and cumulenes