Related Concept Videos
02:52Stereoisomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
02:05Prochirality
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
02:34Structural Isomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
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Related Experiment Video
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06:35
Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
Published on: February 15, 2016
Chromism based on supramolecular H-bonds.
Xiaowei Yu1, Chuanlang Zhan, Xunlei Ding
1Beijing National Laboratory of Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing, PR China.
Physical Chemistry Chemical Physics : PCCP
|June 18, 2013
Summary
A novel chromism was observed in perylene diimide (PDI) derivatives. Trifluoroacetic acid (TFA) induces a dramatic color change in PDI solutions through step-by-step hydrogen bonding, altering electronic energy levels.
Area of Science:
- Organic Chemistry
- Photochemistry
- Materials Science
Background:
- Solvatochromism typically involves compounds with significant differences in ground and excited state dipole moments.
- Perylene diimide (PDI) derivatives usually exhibit weak color changes due to minimal dipole moment differences between states.
Purpose of the Study:
- To investigate a new chromism in a PDI derivative induced by trifluoroacetic acid (TFA).
- To elucidate the mechanism of color change via step-by-step hydrogen bonding and its effect on electronic energy levels.
Main Methods:
- Synthesis and characterization of PDI derivatives.
- Spectroscopic analysis (UV-vis absorption, fluorescence, NMR) in the presence of varying TFA concentrations.
- Electrochemical measurements (cyclic voltammetry).
- Quantum chemical calculations.
Main Results:
- A dilute dichloromethane (DCM) solution of a tetra-substituted PDI derivative showed a distinct color change from red to dark blue with significant red-shifts in absorption (32 nm) and fluorescence (45 nm) upon addition of TFA.
- Step-by-step hydrogen bonding of TFA with the PDI chromophore (imide C=O, bridged -O-, TFA molecules) lowered the LUMO energy level more than the HOMO.
- The extent of color change correlated with the number of bay-substituted phenoxyl groups and the acidity of the carboxylic acid, with protons being essential for the observed chromism.
Conclusions:
- A novel chromism driven by strong hydrogen bonding interactions has been discovered in PDI derivatives.
- The phenomenon is tunable by modifying the PDI structure and the interacting acid.
- This finding opens avenues for developing new chromogenic materials sensitive to acidic environments.