Stark absorption spectroscopy of flavin mononucleotide and derivatives of pyrene, xanthene, phenoxazine, and thienotetracene

Abstract

Stark absorption spectroscopy provides quantitative information on charge redistribution of a chromophore, specifically its difference dipole moment (Δ) and change in polarizability , concurrent with photoexcitation. Δ and have been the focus of fundamental studies of quantum theory and electron transfer and, more recently, have garnered interest in light harvesting, nonlinear optics, and quantum information science. In this work, we quantify the photophysical and electro-optical properties of six conjugated organic molecules—two field standards, two common dyes, and two substituted thienotetracenes. Specifically, we quantify their transition energies, transition dipole moments (μ), |Δ|, , and ζ, the angle between μ and |Δ|, using a high-sensitivity Stark absorption spectrometer. We first characterized two field standards, flavin mononucleotide and 8-hydroxypyrene-1,3,6-trisulfonic acid, in water:glycerol. The |Δ|, , and ζ values we measured for their first two electronic transitions generally agreed with those reported in past literature precedents, validating our approach. Next, we characterized two common dyes, rhodamine B and Nile blue A, in ethanol. The Δ values for their first electronic transition generally agreed with the corresponding values reported in the literature obtained via the solvatochromic approach. Lastly, we characterized the first electronic transition of two thienotetracenes, which differ by the presence and absence of a biomolecule-compatible tag, a N-hydroxysuccinimide (NHS) ester group, attached directly to the thienotetracene core. We found that the presence of the NHS ester group increases |Δ|, likely due to its electron withdrawing nature, and decreases . Overall, all six molecules were moderately-strong light absorbers (μ ∼ 3–9 D) with appreciable |Δ| (∼2–7 D) and ranging from 0–200 ų. This work demonstrates the broad applicability and robustness of Stark spectroscopy and will ideally open the door for future researchers interested in the technique.