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However, as the pH increases beyond 8.2, that central carbon becomes part of a double bond becoming sp 2 hybridized and leaving a p orbital to overlap with the π-bonding in the rings. This makes the three rings conjugate together to form an extended chromophore absorbing longer wavelength visible light to show a fuchsia color. [ 7 ]
Transition metal compounds are often colored because of transitions of electrons between d-orbitals of different energy. (see Transition metal#Colored compounds ). Organic compounds tend to be colored when there is extensive conjugation , causing the energy gap between the HOMO and LUMO to decrease, bringing the absorption band from the UV to ...
F A (I) centers have similar properties as regular F centers, whereas F A (II) centers cause two potential wells to form in the excited state due to the repositioning of a halide ion. Similar to the F A is the F B center, which consists of an F center with two neighbouring positive ions replaced by a positive ion of a different kind.
The beginning of modern science-based chemical or electrochemical coloring of metals is marked by Leopoldo Nobili's (1784–1835) discovery of Nobilis colored rings in 1826. [10] Leonhard Elsner, Alexander Watt, Antoine César Becquerel (1788–1878) and Rudolf Christian Böttger (1806–1881) are also important people in the early history of ...
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Several of the CPK colors refer mnemonically to colors of the pure elements or notable compound. For example, hydrogen is a colorless gas, carbon as charcoal, graphite or coke is black, sulfur powder is yellow, chlorine is a greenish gas, bromine is a dark red liquid, iodine in ether is violet, amorphous phosphorus is red, rust is dark orange-red, etc.
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Another example of a leuco dye is the crystal violet lactone, which in its lactone form is colorless or slightly yellowish, but in low pH, when it is protonated, it becomes intensely violet. [1] Other examples are phenolphthalein and thymolphthalein , colorless in acidic to neutral pH, but becoming pink and blue in alkaline environment.