Ultrafast dynamics of single molecules

Abstract

The detection of individual molecules has found widespread application in molecular biology, photochemistry, polymer chemistry, quantum optics and super-resolution microscopy. Tracking of an individual molecule in time has allowed identifying discrete molecular photodynamic steps, action of molecular motors, protein folding, diffusion, etc. down to the picosecond level. However, methods to study the ultrafast electronic and vibrational molecular dynamics at the level of individual molecules have emerged only recently. In this review we present several examples of femtosecond single molecule spectroscopy. Starting with basic pump-probe spectroscopy in a confocal detection scheme, we move towards deterministic coherent control approaches using pulse shapers and ultra-broad band laser systems. We present the detection of both electronic and vibrational femtosecond dynamics of individual fluorophores at room temperature, showing electronic (de)coherence, vibrational wavepacket interference and quantum control. Finally, two colour phase shaping applied to photosynthetic light-harvesting complexes is presented, which allows investigation of the persistent coherence in photosynthetic complexes under physiological conditions at the level of individual complexes.

Ab initio multiscale simulation of high-order harmonic generation in solids

“…Since interband polarization is much more effectively suppressed by previously proposed ultrashort dephasing times than coherent intraband dynamics, the contribution of interband polarization may be significantly higher than expected when realistic dephasing times are employed. The present findings have also important implications for other ultra-fast processes, for example, probing of biomaterials by transmission of a broadband pulse [46]. Extraction of information on the presence of specific molecules will require the disentangling of the non-linear molecular response from mesoscopic light transport effects.…”

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

“…A particularly important question in this regime concerns the impact of unavoidable electronic and structural disorder from complex to complex [138] on the coherent transport. As such heterogeneity cannot be resolved by conventional time-resolved spectroscopy, ultrafast singlemolecule spectroscopy [105,139] was applied on individual complexes at room temperature to address this issue. [109] To probe coherence in this B800-B850 transfer step in single LH2, a two-color experiment was employed in which a first pulse is resonant with the B800 absorption and a second timedelayed and phase-controlled pulse is resonant with the optically allowed bottom B850 exciton states (Figure 8a).…”

“…To this end, pulse-shaping techniques were combined with confocal microscopy that allows to efficiently collect the fluorescence signal of single objects. [104,105] The general idea behind this approach is to excite a single molecule with a sequence of two ultrashort pulses with controlled delay time as well as phase difference between the pulses. The first pulse creates coherences between the ground and excited electronic states or coherences between excited states (electronic or vibronic).…”

Optimizing sparse sampling for 2D electronic spectroscopy

“…19 One advantage of detecting incoherent signals is that it permits the study of lowdensity samples, even down to the single-molecule limit. 20 A detailed comparison of various experimental 2D spectroscopy approaches can be found in a recent review. 21 Multidimensional spectroscopy in general requires multidimensional scanning of parameters such as time delays or phases.…”