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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Shape-persistent macrocycles functionalised with coumarin dyes: acid-controlled energy- and electron-transfer
Carlo Giansante1, Paola Ceroni, Margherita Venturi
1Dipartimento di Chimica G. Ciamician, Università di Bologna, Via Selmi 2, 40126 Bologna , Italy.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|October 24, 2008
Summary
This study explores fluorescent triads with macrocyclic backbones. Protonation of these triads causes significant, reversible changes in their optical properties due to altered excited-state energy levels.
Area of Science:
- Photochemistry
- Supramolecular Chemistry
- Spectroscopy
Background:
- Investigated three fluorescent triads: C2-M-C2, C343-M-C343, and C2-M-C343.
- M is a macrocyclic hexagonal backbone with 2,2'-bipyridine (bpy) units; C2 and C343 are coumarin dyes.
- All components exhibit strong fluorescence.
Purpose of the Study:
- To investigate the spectroscopic properties (absorption, emission, lifetimes) of these triads.
- To understand how protonation affects their photophysical behavior.
- To explore the potential for acid-responsive optical materials.
Main Methods:
- Spectroscopic analysis including absorption and emission spectra.
- Measurement of fluorescence lifetimes.
- Investigation of protonation equilibria using acid-base titrations.
Main Results:
- Excitation of the macrocyclic backbone (M) efficiently transfers energy to the coumarin units.
- Protonation of bpy units in M leads to monoprotonated and diprotonated species.
- Further protonation of coumarin units results in four distinct protonation equilibria.
- Protonation induces significant, reversible changes in absorption and fluorescence properties.
- Changes are attributed to excited-state energy level inversion and electron-transfer quenching.
Conclusions:
- The studied triads exhibit tunable spectroscopic properties responsive to protonation.
- Protonation reversibly alters fluorescence and absorption characteristics.
- These systems show potential for developing acid-sensitive fluorescent probes or materials.
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