Room-temperature ultrafast non-linear spectroscopy of a single molecule

We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecules by probing the third-order nonlinear optical susceptibility. A non-colinear 3-pulse scheme is developed to probe the ultrafast dynamics of excited electronic states using the optical Kerr effect by time-resolved polarization spectroscopy. Optical heterodyne and optical homodyne detection are demonstrated to measure the third-order nonlinear optical response for the S1 excited ...

Single-molecule biophysics has transformed our understanding of the fundamental molecular processes involved in living biological systems, but also of the fascinating physics of life. Far more exotic than a collection of exemplars of soft matter behaviour, active biological matter lives far from thermal equilibrium, and typically covers multiple length scales from the nanometre level of single molecules up several orders of magnitude to longer length scales in emergent struct...

Fluctuation in fluorescence emission of immobilized single molecule is typically ascribed to the chromophore's intrinsic structural conformations and the influence of local environmental factors. Despite extensive research over several decades since its initial observation, a direct connection between these spectral fluctuations and the rearrangement of emission dipole orientations has remained elusive. In this study, we elucidate this fundamental molecular behavior and its u...

We report the observation of ultralong coherence times in the purely electronic zero-phonon line emission of single terrylenediimide molecules at 1.4 K. Vibronic excitation and spectrally resolved detection with a scanning Fabry-Perot spectrum analyzer were used to measure a linewidth of 65 MHz. This is within a factor of 1.6 of the transform limit. It therefore indicates that single molecule emission may be suited for applications in linear optics quantum computation. Additi...

Electron motion on the (sub-)femtosecond time scale constitutes the fastest response in many natural phenomena such as light-induced phase transitions and chemical reactions. Whereas static electron densities in single molecules can be imaged in real-space using scanning tunnelling and atomic force microscopy, probing real-time electron motion inside molecules requires ultrafast laser pulses. Here, we demonstrate an all-optical approach to imaging an ultrafast valence electro...

In this paper, single-molecule spectroscopy experiments based on continuous laser excitation are characterized through an open quantum system approach. The evolution of the fluorophore system follows from an effective Hamiltonian microscopic dynamic where its characteristic parameters, i.e., its electric dipole, transition frequency, and Rabi frequency, as well as the quantization of the background electromagnetic field and their mutual interaction, are defined in an extended...

The advent of single molecule optics has had a profound impact in fields ranging from biophysics to material science, photophysics, and quantum optics. However, all existing room-temperature single molecule methods have been based on fluorescence detection of highly efficient emitters. Here we demonstrate that standard, modulation-free measurements known from conventional absorption spectrometers can indeed detect single molecules. We report on quantitative measurements of th...

We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending the well-known technique of Optical-Kerr Effect (OKE) spectroscopy to excited electronic states. The third-order non-linear response of the excited molecular ensemble is highly sensitive to details of excited state character and geometries and is measured using two femtosecond pulses following a third fem...

Revealing possible long-living coherence in ultrafast processes allows detecting genuine quantum mechanical effects in molecules. To investigate such effects from a quantum chemistry perspective, we have developed a method for simulating the time evolution of molecular systems, based on ab initio calculations that includes relaxation and environment-induced dephasing of the molecular wave function, whose rates are external parameters. The proposed approach combines a quantum ...

New experimental techniques based on non-linear ultrafast spectroscopies have been developed over the last few years, and have been demonstrated to provide powerful probes of quantum dynamics in different types of molecular aggregates, including both natural and artificial light harvesting complexes. Fourier transform-based spectroscopies have been particularly successful, yet 'complete' spectral information normally necessitates the loss of all information on the temporal se...