![]() ![]() The FT data yield simultaneously detected SM excitation and emission spectra in the form of a 2D excitation–emission matrix (EEM), which contains all information available in a steady-state emission experiment. The resulting implementation is robust with high inherent phase stability no active phase stabilization is necessary when recording spectral interferograms of individual molecules at room temperature. Here we use a common-path interferometer ( 16, 17) for the combined detection of time-resolved or dispersed emission with FT-based excitation spectroscopy of single emitters. Recording the emission intensity as a function of t 1 results in an interferogram, which after an FT yields the frequency-resolved excitation spectrum. The principles of FT spectroscopy are well known from ensemble measurements ( 14, 15): Fundamentally, an FT instrument requires a broadband excitation source coupled to an interferometer capable of generating two collinear replicas of the excitation beam with a time delay t 1. While the narrow-band approach has been demonstrated in several experiments ( 8– 10), a Fourier-transform (FT)–based approach has received recent attention ( 11– 13). Attempts at reintroducing molecular ground-state information by recording fluorescence excitation spectra have been made both by the tunable narrow-band excitation approach and by interferometry. ![]() Emission spectra primarily report the relaxed environment of the photoexcited molecules, and thus information on the ground-state equilibrium properties of the system is lost. A consequence of measuring emission rather than excitation spectra, however, is that most SMS experiments provide little information on the environment of ground-state molecules. Not only does this allow photoinduced excited-state processes to be followed, it also greatly simplifies and accelerates the experiment. ![]() Meanwhile, most modern SMS implementations rely on fixed-wavelength excitation and rather report emission spectra, fluorescence lifetimes, or intensity fluctuations ( 7). The first luminescence-based SMS experiments were realized by tunable narrow-band laser sources, and reported fluorescence excitation spectra of dyes embedded in Shpolskii matrices at subliquid helium temperatures ( 2, 5, 6). This analysis finally reveals that environmental fluctuations between the donor and acceptor in the dyads are not correlated. We analyze the resulting spectral parameters in terms of optical lineshape theory to obtain detailed information on the interactions of the emitters with their nanoscopic environment. We demonstrate the technique by simultaneously collecting room-temperature excitation and emission spectra of individual terrylene diimide molecules and donor–acceptor dyads embedded in polystyrene. Here we address this problem by demonstrating simultaneous collection of fluorescence emission and excitation spectra using a compact common-path interferometer and broadband excitation, which is implemented as an extension of a standard SMS microscope. ![]() While the last several decades have seen substantial refinement of SMS techniques, recording excitation spectra of single emitters still poses a significant challenge. Single-molecule spectroscopy (SMS) provides a detailed view of individual emitter properties and local environments without having to resort to ensemble averaging. ![]()
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