Several closely related third‐order nonlinear time‐resolved spectroscopic techniques, pump/probe transient absorption, transient grating, and three pulse stimulated photon echo peak shift measurements, are investigated theoretically and experimentally. It is shown in detail, through the consideration of response functions and numerical simulations including both finite pulse durations and detuning from exact resonance, how the solvation dynamics are manifested in these third‐order nonlinear time‐resolved spectroscopies. It is shown that the three pulse stimulated photon echo peak shift measurement and the transient grating measurement can give accurate dynamical information, whereas transient absorption may not be a reliable technique for a study of solvation dynamics in some cases. The contribution of very slow or static (inhomogeneous) components to the dynamics, however, can only be obtained from the three pulse echo peak shift measurements. Comprehensive experimental measurements are presented to illustrate and corroborate the calculations. We show that it is possible to separate the intramolecular vibrational and solvent contributions to the dephasing (or optical lineshape). Furthermore it is shown that the solvation of polar solutes in polar protic solvents has rather universal characteristics. The initial ultrafast process, usually identified as an inertial response of solvent molecules, occurs on a ∼100 fs time scale, and is essentially identical in methanol, ethanol, and butanol. The amplitude of this ultrafast component does, however, decrease with increasing alcohol size in 1‐alkanols. The diffusive (≳0.5 ps) regime of the solvation process shows a strong solvent dependence, and may be described satisfactorily by dielectric relaxation theories.

http://www.cchem.berkeley.edu/grfgrp/Papers/1996%20Joo%20JChemPhys104.pdf

Third-order nonlinear time domain probes of solvation dynamics

In 1970, three laboratories independently made a discovery that, for aromatic fluorophores embedded into different rigid and highly viscous media, the spectroscopic properties do not conform to classical rules. The fluorescence spectra can depend on excitation wavelength, and the excited-state energy transfer, if present, fails at the "red" excitation edge. These red-edge effects were related to the existence of excited-state distribution of fluorophores on their interaction energy with the environment and the slow rate of dielectric relaxation of this environment. In these conditions the site-selection can be provided by variation of the energy of illuminating light quanta, and the behaviour of selected species can be followed as a function of time and other variables. These observations found extensive application in different areas of research: colloid and polymer science, molecular biophysics, photochemistry and photobiology. In particular, they led to the development of very productive methods of studying the dynamics of dielectric relaxations in protein and membranes, using the tryptophan emission and the emission of a variety of probes. These studies were extended to the time domain with the observation of new site-selective effects in emission intensity and anisotropy decays. They stimulated the emergence and development of cryogenic energy-selective and single-molecular techniques that became valuable tools in their own right in chemistry and biophysics research. Site-selection effects were discovered for electron-transfer and proton-transfer reactions if they depended on the dynamics of the environment. This review is focused on the progress in the field of red-edge effects, their applications and prospects.

The red‐edge effects: 30 years of exploration

Stable ‘gap’ in absorption spectra of solid solutions of organic molecules by laser irradiation

Homogeneous line broadening of optical transitions of ions and molecules in glasses

The initial steps toward optical detection and spectroscopy of single molecules in condensed matter arose out of the study of inhomogeneously broadened optical absorption profiles of molecular impurities in solids at low temperatures. Spectral signatures relating to the fluctuations of the number of molecules in resonance led to the attainment of the single-molecule limit in 1989 using frequency-modulation laser spectroscopy. In the early 90s, many fascinating physical effects were observed for individual molecules, and the imaging of single molecules as well as observations of spectral diffusion, optical switching and the ability to select different single molecules in the same focal volume simply by tuning the pumping laser frequency provided important forerunners of the later super-resolution microscopy with single molecules. In the room temperature regime, imaging of single copies of the green fluorescent protein also uncovered surprises, especially the blinking and photoinduced recovery of emitters, which stimulated further development of photoswitchable fluorescent protein labels. Because each single fluorophore acts a light source roughly 1 nm in size, microscopic observation and localization of individual fluorophores is a key ingredient to imaging beyond the optical diffraction limit. Combining this with active control of the number of emitting molecules in the pumped volume led to the super-resolution imaging of Eric Betzig and others, a new frontier for optical microscopy beyond the diffraction limit. The background leading up to these observations is described and current developments are summarized.

Single‐Molecule Spectroscopy, Imaging, and Photocontrol: Foundations for Super‐Resolution Microscopy (Nobel Lecture)

The effect of fine structure appearance in laser-excited fluorescence spectra of organic compounds in solid solutions

Extreme narrowing of bands in the fluorescence excitation spectra of organic molecules in solid solutions

/pdf/photochemical-and-photophysical-hole-burning-in-electronic-3rfcdvpqwe.pdf

R.I. Personov

Papers

Stable ‘gap’ in absorption spectra of solid solutions of organic molecules by laser irradiation

The effect of fine structure appearance in laser-excited fluorescence spectra of organic compounds in solid solutions

Extreme narrowing of bands in the fluorescence excitation spectra of organic molecules in solid solutions

Photochemical and photophysical hole burning in electronic spectra of complex organic molecules