Nanomechanical properties of molecular-scale bridges as visualised by intramolecular electronic energy transfer

Abstract

EDGE ARTICLEAndrew J. deMello, Joshua B. Edel et al. Rapid cell extraction in aqueous twophase microdroplet systems PERSPECTIVE Barry M. Trost et al. Catalytic asymmetric allylic alkylation employing heteroatom nucleophiles: a powerful method for C-X bond formationA series of molecular dyads has been synthesized and fully characterised. These linear, donor-spaceracceptor compounds comprise terminal dyes selected to exhibit intramolecular electronic energy transfer (EET) along the molecular axis. The spacer is built by accretion of ethynylene-carborane units that give centre-to-centre separation distances of 38, 57, 76, 96, and 115 Å respectively along the series. The 10 probability of one-way EET between terminals depends on the length of the spacer but also on temperature and applied pressure. Throughout the series, the derived EET parameters are well explained in terms of through-space interactions but the probability of EET is higher than predicted for the fully extended conformation except in a glassy matrix at low temperature. The implication is that these spacers contract under ambient conditions, with the extent of longitudinal contraction increasing under pressure 15 but decreasing as the temperature is lowered. Longer bridges are more susceptible to such distortion, which is considered to resemble a concertina effect caused by out-of-plane bending of individual subunits. The dynamics of EET can be used to estimate the strain energy associated with molecular contraction, the amount of work done in effecting the structural change and the Young's modulus for the bridge.

Artificial light-harvesting arrays for solar energy conversion

“…This distance-independent EET is in sharp contrast to what 35 happens when the bridge does not participate in super-exchange interactions. Now the rate of EET falls dramatically as the separation distance increases, as has been demonstrated 27 for the series of para-carborane bridged dyads illustrated in Figure 6. It has not been easy to identify rigid bridges that span the necessary 40 range of distances needed to effect such a study and even these structures are subjected to geometry fluctuations under ambient conditions.…”

Exciplex Emission from a Boron Dipyrromethene (Bodipy) Dye Equipped with a Dicyanovinyl Appendage

“…This is to be expected on the basis of the fact that pressure raises the density of MTHF and this causes an increase in the effective concentration of the solute, [46] although not sufficient to induce self-association. This is to be expected on the basis of the fact that pressure raises the density of MTHF and this causes an increase in the effective concentration of the solute, [46] although not sufficient to induce self-association.…”

Cyclophane‐Based Fluorescence Tuning Induced by Hydrostatic Pressure Changes

“…Mechanical stimuli can vary photoluminescence properties of organic materials in solution and/or solid states . Mechanoresponsive organic compounds are promising candidates of indicator of applied force, optical data storage and mechano‐bioimaging probes for living cells.…”