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When ionic dyes are close together, the internal Coulomb interaction may affect their photophysics and the energy‐transfer efficiency. To explore this, we have prepared triangular architectures of three rhodamines connected to a central triethynylbenzene unit (1,3,5‐tris(buta‐1,3‐diyn‐1‐yl)benzene) based on acetylenic coupling reactions and measured fluorescence spectra of the isolated, triply charged ions in vacuo. We find from comparisons with previously reported monomer and dimer spectra that while polarization of the π‐system causes redshifted emission, the separation between the rhodamines is too large for a Stark shift. This picture is supported by electrostatic calculations on model systems composed of three linear and polarizable ionic dyes in D3h configuration: The electric field that each dye experiences from the other two is too small to induce a dipole moment, both in the ground and the excited state. In the case of heterotrimers that contain either two rhodamine 575 (R575) and one R640 or one R575 and two R640, emission is almost purely from R640 although the polarization of the π‐system expectedly diminishes the dipole‐dipole interaction. [ABSTRACT FROM AUTHOR]

Abstract: Donor–donor′–acceptor triads (1, 2), based on [3.3]paracyclophane ([3.3]PCP) as a bridge, with electron‐donating properties (D′) using 1,4‐dithiafulvene (DTF; TTF half unit) as a donor and dicyanomethylene (DCM; TCNE half unit) or an ethoxycarbonyl‐cyanomethylene (ECM) as an acceptor were designed and synthesized. The pulse radiolysis study of 1 a in 1,2‐dichloroethane allowed the clear assignment of the absorption bands of the DTF radical cation (1 a.+), whereas the absorption bands due to the DCM radical anion could not be observed by γ‐ray radiolysis in 2‐methyltetrahydrofuran rigid glass at 77 K. Electrochemical oxidation of 1 a first generates the DTF radical cation (1 a.+), the absorption bands of which are in agreement with those observed by a pulse radiolysis study, followed by dication (1 a2+). The ESR spectrum of 1 a.+ showed a symmetrical signal with fine structure and an ESR simulation predicted that the spin of 1 a.+ is delocalized over S and C atoms of the DTF moiety and the central C atom of the trimethylene bridge bearing the DTF moiety. Pulse radiolysis, ESR, and electrochemical studies indicate that the DTF radical cation of 1 a.+ is more stable than that of 6.+, and the latter shows a strong tendency to dimerize. This result indicates that the [3.3]PCP moiety as a bridge can stabilize the DTF radical cation more than the 1,3‐diphenylpropane moiety because of kinetic stability due to its rigid structure and the weak electronic interaction of DTF and DCM moieties through [3.3]PCP. [ABSTRACT FROM AUTHOR]

Energy transfer, gas-phase fluorescence, mass spectrometry, Stark shift, triads Cover Feature: Triangular Rhodamine Triads and Their Intrinsic Photophysics Revealed from Gas-Phase Ion Fluorescence Experiments (Chem. Eur. J. 42/2021) Keywords: energy transfer; gas-phase fluorescence; mass spectrometry; Stark shift; triads EN energy transfer gas-phase fluorescence mass spectrometry Stark shift triads 10777 10777 1 07/28/21 20210726 NES 210726 B The LUminescence iNstrument in Aarhus (LUNA) b , which is depicted in the cover image, was used for gas-phase ion fluorescence experiments on triangular rhodamine triads where each rhodamine dye carries a positive charge. [Extracted from the article]