Fluorescence-detected two-dimensional electronic spectroscopy of a single molecule

TL;DR

This paper presents a novel method combining fluorescence detection and two-dimensional spectroscopy to study ultrafast processes in single molecules at room temperature, enabling insights into energy transfer at the quantum level.

Contribution

It introduces a new technique for performing 2D spectroscopy on individual molecules using fluorescence detection, overcoming previous temporal resolution limitations.

Findings

Successful measurement of 2D spectra of single molecules at room temperature.

Method applicable to various single emitters for ultrafast energy transfer studies.

Demonstrated feasibility with dibenzoterrylene in a polymer matrix.

Abstract

Single-molecule fluorescence spectroscopy is a powerful method that avoids ensemble averaging, but its temporal resolution is limited by the fluorescence lifetime to nanoseconds at most. At the ensemble level, two-dimensional spectroscopy provides insight into ultrafast femtosecond processes such as energy transfer and line broadening, even beyond the Fourier limit, by correlating pump and probe spectra. Here, we combine these two techniques and demonstrate 2D spectroscopy of individual molecules at room temperature using the example of dibenzoterrylene (DBT) in a polymer matrix. We excite the molecule in a confocal microscope with a phase-modulated train of femtosecond pulses and detect the emitted fluorescence with single-photon counting detectors. Using a phase sensitive detection scheme, we were able to measure the nonlinear 2D spectra of most of the DBT molecules we studied. Our method is applicable to a wide range of single emitters and opens new avenues for understanding energy transfer in single quantum objects on ultrafast time scales.