Solvent Controlled Energy Transfer Processes in Triarylamine-Triazole Based Dendrimers

Abstract

Fluorescence upconversion measurements of three different dendrimers G1 –G3 based on triarylamines connected by triazole linkers show a strong and fast initial decay of fluorescence anisotropy for t < 2 ps followed by anisotropy decay on a much longer time scale (10–100 ps). At the same time, a pronounced solvent relaxation takes place. Comparison of the decay data in different solvents revealed that the initial decay of fluorescence anisotropy is governed by a competition of solvent relaxation and incoherent hopping of energy between the different dendrimer branches. Thus, it is decisive to discriminate between energy transfer processes in the Franck–Condon state or in the solvent relaxed state. We demonstrate that even for charge transfer chromophores, where a large Stokes shift leads to very weak spectral overlap of donor fluorescence and acceptor absorption, rapid homotransfer is possible if there is sufficient spectral overlap with the time zero fluorescence spectrum.

Excited-state intramolecular proton transfer of 2-acetylindan-1,3-dione studied by ultrafast absorption and fluorescence spectroscopy

“…For the fluorescence upconversion measurement, a commercial setup (Halcyone, Ultrafast Systems) was used with the details provided elsewhere 51 . Briefly, part of the fundamental beam of another amplified Ti:Sapphire laser (Solstice, Spectra-Physics, λ c  = 800 nm, Δτ = 100 fs, ν rep  = 1 kHz) was used to pump an optical parametric amplifier (TOPAS, Light Conversion) to generate the UV pump beam centered at 300 nm.…”

“…The upconverted light was focused onto the entrance slit of a double monochromator and detected by a photomultiplier tube. The instrument response was estimated to be 350 fs by measuring stray light or Raman signals of the neat solvents 51 . The femtosecond fluorescence decays were deconvoluted globally (with OriginPro 2015 software) using a Gaussian-shaped IRF (fixed at 350 fs) and a multi-exponential function, $Ifalse(\lambda ,tfalse)=\sum _i{\alpha }_{i}false(\lambda false)\hspace{0.17em}\text{exp}\hspace{0.17em}false[-t/{\tau }_{i}false(\lambda false)false]$, where α i ( λ ) are pre-exponential factors, τ i (λ) are the decay times, and $\sum {\alpha }_{i}false(\lambda false)=1$.…”

Photophysical and Protonation Time Resolved Studies of Donor–Acceptor Branched Systems With Pyridine Acceptors

“…Depending on the strength of the coupling among branches, coherent and/or incoherent excitation energy transfer (EET) phenomena, taking place on the tens of fs up to the few ps timescale are observed, which are typically followed by ICT and solvent relaxation leading to solvent relaxed CT states. [12][13][14][15] It is understood that a plethora of competing dynamic phenomena occur after excitation of the branched compounds with ultrashort laser pulses and their discrimination is not always straightforward.…”

CAST: A new program package for the accurate characterization of large and flexible molecular systems

“…The first interface implemented accesses to the MOPAC2012 program, which is a program package for semiempirical calculations so that the CAST program can be used to perform semiempirical MD or TS runs. Application examples are 1,7‐diphenoxy‐perylene bisimides, perylene bisimide macrocycles, and triarylamine‐triazole‐based dendrimers . The interface had to be implemented as a system call.…”