Two‐Photon Voltmeter for Measuring a Molecular Electric Field

Abstract

We present a new approach for determining the strength of the dipolar solute-induced reaction field, along with the ground- and excited-state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one-photon and two-photon absorption measurements. We verify the approach on two benchmark chromophores N,N-dimethyl-6-propionyl-2-naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum-chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–107 V cm−1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close-range molecular interaction.

Symmetry Breaking in Pyrrolo[3,2‐b]pyrroles: Synthesis, Solvatofluorochromism and Two‐photon Absorption

“…The possibility of spontaneous breaking of ground‐ and excited‐state inversion symmetry in nominally quadrupolar chromophores was suggested earlier by Terenziani et al., who considered a pseudo Jahn–Teller‐type mechanism being responsible for large solvatofluorochromism . In our case, the degree by which the intrinsic symmetry may be becomes “broken” could be indirectly quantified by evaluating the ratio between σ 2PA and the linear extinction at the very red side of the spectra (i.e., at the wavelengths where the two spectral profiles coincide), using the relation: …”

“…where Δ μ is the change of permanent electric dipole moment (in Debye), n is the solvent index of refraction, λ 2PA is the wavelength (nm), ϵ M is the molar extinction coefficient (M −1 cm −1 ), and σ 2PA is the 2PA cross‐section, expressed in Göppert–Mayer units (1 GM=10 −50 cm 4 photon −1 s −1 ). We note that even though Equation is commonly applied only to dipolar dyes, there is accumulating experimental evidence that this relation may be also extended to the lowest‐energy, purely electronic transition of nominally symmetric systems, where the dipole moment is created by a spontaneous symmetry breaking mechanism . Figure (top panel) shows the above dipole moment change function plotted for 8 along with the Gaussian decomposition components of the linear absorption spectrum.…”

Quantitative description of MLCT transitions in ruthenium polypyridyl complexes probed by two-photon absorption spectroscopy

“…The 2PA cross-sections over the wavelength range of 680 -1020 nm for [Ru(bpy)3] 2+ and [Ru(phen)3] 2+ are shown as solid lines in Figure 3. Applying the two-state model of 2PA [1] to the lowest-energy transitions, we can evaluate the difference in the ground-and excited state dipole moments according to the equation:…”

“…Quantitative two-photon absorption (2PA) spectroscopy is a versatile technique that can measure changes of permanent electric dipole moment. [1,2] We investigated the 2PA spectra of [Ru(bpy)3] 2+ and [Ru(phen)3] 2+ dissolved in water (H2O), dimethylsulfoxide (DMSO), acetonitrile (ACN), and dichloromethane (DCM), and use a two-level model of 2PA applied to the lowest-energy transitions to estimate the value of  in different solvents.…”

Pulse-shaped two-photon excitation of a fluorescent base analogue approaches single-molecule sensitivity

“…Unlike the 1P absorption coefficient, which is determined by the transition dipole moment between ground and excited states, the 2P cross section, s 2 , depends on both the transition dipole moment and the change in permanent dipole moment on excitation (in a two-level model for a dipolar chromophore), as expressed in eqn (4) s 2 p |m 10 | 2 |Dm 10 | 2 (4) wherem 10 is the transition dipole moment between the ground state (S 0 ) and the excited state (S 1 ), and Dm 10 is the difference between the permanent dipole moments of S 1 and S 0 . 29 The difference in relative 2P cross sections of the two tautomers, compared with their relative 1P cross sections can, therefore, be attributed to a greater change in permanent dipole moment on excitation for the t 1 tautomer. We end this section with a caveat regarding the calculation of the 2P cross section from the experimentally measured parameter, the 2P brightness, s 2 f, which is the product of the quantum yield and the 2P cross section.…”