Hypsochromic or Blue Shift

The intermolecular attractive force known as hydrogen bonding can occur when a molecnle contains hydrogen covalently bound to oxygen or nitrogen. The O-H or N-H bond is highly polarized  

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In general, auxochromic substitution of chromophores causes bathochromic shifts and increases in intensity for 7t —> k transitions, and hypsochromic or blue shifts (to shorter wavelengths) for n K transitions. The shifts are explainable in terms of mesomeric resonance) effects caused by interaction of lone pair electrons associated with such auxochromes as —OH, —Cl, —NH2 with the k system of the chromophore. This leads to... 

The absorbance maximum of phenols is increased by the addition of base and formation of the phenolate ion, with an associated absorbance shift to longer wavelength (a bathochromic or red shift), whilst the absorbance maximum of anilines is decreased by the addition of acid, which causes protonation of the amine and loss of the lone pair overlap with the K-system, leading to an absorbance shift to shorter wavelength (a hypsochromic or blue shift). 

The term "solvatochromism describes a significant change in position or intensity of an absorption or emission band of a compound in solution, when the polarity of the medium is changed. A bathochromic (or red) shift of the absorption band with increasing solvent polarity is known as positive solvatochromism The corresponding hypsochromic (or blue) shift is termed negative solvatochromism. 

A shift in A,max to shorter wavelength is called a hypsochromic effect, or blue shift, and usually occurs when compounds with a basic auxochrome ionise and the lone pair is no longer able to interact with the electrons of the chromophore. Hypsochromic effects can also be seen when spectra are run in different solvents or at elevated temperatures. Spectral shifts of this type can be used to identify drugs that contain an aromatic amine functional group, e.g. the local anaesthetic benzocaine (see Figure 7.9). 

Hypsochromic A blue shift (to shorter wavelengths) in the absorbance or emission spectrum. 

A hypsochromic effect, or blue shift, is the opposite effect, and consists of the displacement of the absorption maximum towards shorter wave-lengths. It can be produced by loss of conjugation or a change in the medium. 

The hypsochromic shift (or blue shift) is a shift to shorter wavelengths. 

The extinction coefficients of carotenoids have been listed completely bnt solvent effects can shift the absorption patterns. If a colorant molecnle is transferred into a more polar environment, then the absorption will be snbjected to a bathochro-mic (red) shift. If the colorant molecnle is transferred into a more apolar enviromnent, the absorption will be subjected to a hypsochromic (blue) shift. If a carotenoid molecule is transferred from a hexane or ethanol solution into a chloroform solution, the bathochromic shift will be 10 to 20 nm. 

The absorption band occurs at shorter wavelength in a polar solvent than in a nonpolar solvent (the absorption shows a blue shift or hypsochromic shift)... 

Shifts in absorption spectra due to the effect of substitution or a change in environment (e.g. solvent) will be discussed in Chapter 3, together with the effects on emission spectra. Note that a shift to longer wavelengths is called a bathochromic shift (informally referred to as a red-shift). A shift to shorter wavelengths is called a hypsochromic shift (informally referred to as a blue-shift). An increase in the molar absorption coefficient is called the hyperchromic effect, whereas the opposite is the hypochromic effect. 

An effect observed in the spectrum of a chemical species in which a substituent, solvent, change in environment, or other effect causes the electronic absorption spectrum to shift to shorter wavelengths. The opposite effect is referred to as a bathochromic shift. The hypsochromic shift is also known as the blue shift. 

Hypsochromic shift Shift of a spectral band to higher frequency or shorter wavelength upon substitution or change in medium (e.g., solvent). It is informally referred to as a blue shift, and is opposite to bathochromic shift. 

A bathochromic shift (red shift) may occur by a change of medium or by the presence of an auxochrome. A hypsochromic shift (blue shift) may be caused by a change of the medium or by such structural changes like removal of conjugation. 

A shift toward higher frequency is called a blue shift or a hypsochromic shift. Similarly, a shift toward lower frequency is called a red or bathychromic shift, We will use the blue shift, red shift notation. The designation n —ir refers to the excitation of an electron from a nonbonding orbital (an n orbital) to an excited pi orbital of the chromophoric group (a r orbital). The ir — -ir transition is restricted to pi orbitals of the chromophorc, usually from a bonding to an antibonding orbital. The n —ir transitions are forbidden, whereas the T —T transitions may be allowed. 

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