A single molecule can serve as a nanometer-sized detector of acoustic strain. Such a nanomicrophone has the great advantage that it can be placed very close to acoustic signal sources and high sensitivities can be achieved. We demonstrate this scheme by monitoring the fluorescence intensity of a single dibenzoterrylene molecule in an anthracene crystal attached to an oscillating tuning fork. The characterization of the vibration amplitude and of the detection sensitivity is a first step towards detection and control of nanomechanical oscillators through optical detection and feedback.
Triplet states can be interesting for optical switching of molecular fluorescence as well as quantum experiments relying on the manipulation of spin states. However, the ground state of molecules is usually a singlet state. It is therefore interesting to study the intersystem crossing (ISC) rates between singlet and triplet states. We have measured the autocorrelation function of the fluorescence from single perylene molecules in an ortho-dichlorobenzene host matrix at cryogenic temperatures (1.3 K). We observed two time scales in the autocorrelation function corresponding to intersystem crossing to two indistinguishable triplet states (TX and TY) and a third triplet state (TZ). By studying the power dependence of the correlation times and contrasts in the autocorrelation functions of single molecules, we determine the ISC rates of perylene for the first time.
Triggering the release of chemical species through the use of light is crucial for modern microscopy applications, such as single‐molecule localization and, in general, in the regulation of molecular effectors. Herein, we demonstrate a nonlinear‐optical scheme for the control of photorelease. Our system consists of a two‐photon‐absorbing photoremovable protecting group (PPG) bonded to a second chromophore which undergoes photo‐induced detachment and activation upon excitation with λ=850 nm femtosecond pulses. The two‐photon PPG section consists of a cyanine‐type dye, and the releasable section is a highly fluorescent derivatized anthracene chromophore bonded to the cyanine through a photolabile etheric‐meso‐carbon bond. This method allows for the release of a fluorophore following a spatially localized two‐photon excitation event. Both the excitation energy and the long lifetime of the upper excited states of the PPG chromophore are thought to be involved in the release process.
Schiff bases bearing an intramolecular hydrogen bond are known to undergo excited-state intramolecular proton transfer and E-Z isomerization, which are related to their thermochromism and solvatochromism properties. In this study, we explored these ultrafast photoinduced processes for two doubly hydroxylated Schiff bases, salicylidene-2-aminophenol and 2-hydroxynaphthylmethylidene-2-aminophenol. From comparisons with our previously reported results for the parent monohidroxylated Schiff base salicylideneaniline, we were able to establish the lack of an effect of a second intramolecular hydrogen bond in the excited-state intramolecular proton-transfer process. Moreover, we synthesized and studied the photophysics of 14 diphenyl-tin(IV) derivatives with Schiff bases with the same framework as the former two. In these organometallic compounds, we observed an increase of more than 50 times in the excited-state decay times in comparison with those of the free ligands. This finding is attributed to the coordination with the metallic center, which restricts the fluctuations of the geometry of the organic Schiff base skeleton. The emission bands of these complexes can be easily tuned through substitutions at the Schiff base ligand and can be made to be centered well above 600 nm. The much enhanced emissive behavior of all diphenyl-tin(IV) derivatives allowed the study of several properties of their electronically excited states, including the effects of different substituents on their femtosecond and picosecond dynamics. Considering potential applications, we also performed transient absorption experiments to assess the wavelength interval for stimulated emission of this type of compound. Finally, we determined their two-photon absorption cross sections in the 760-820-nm range by measuring their two-photon induced fluorescence excitation spectra. Mainly, our results illustrate that the diphenyl-tin(IV) moiety, thanks to its size and its coordination mode with a single Schiff base, can be coordinated to this versatile framework to obtain tunable optical properties wherein the emissive states can have lifetimes on the nanosecond time scale.
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