Ir-tt* transition

The exact wavelength necessary to effect the ir —tt transition in a con jugated molecule depends on the energy gap between HOMO and LUMQj which in. turn depends on the nature of the conjugated system. Thus, bj measuring the UV spectrum of an unknown, we can derive structural infor< mation about the nature of any conjugated tt electron system present. 

Fig. 2. Resolution of the fluorescence of 2-p-toluidinonaphthalene-6-sulfonate (TNS) in an aqueous suspension of spinach chloroplast membranes treated with Tb. The component ( ) whose contribution increases with [Tb ] arises from a ir —> tt transition and reflects membrane-bound TNS. The remaining two components arise from a charge-transfer excited state and reflect free TNS. One component (A) is attributed to TNS with the nitrogen atom either protonated or involved in hydrogen bonding to the solvent, and the other (O) is associated with nonprotonated TNS.

The value of refers to liie longest wavelenglii ir —> -tt transition. 

Absorption band due to ir —> tt transition in conjugated polyene chain. Chemical shift of olefinic proton in cis form. 

UV-VIS Aldehydes and ketones have two absorption bands in the ultraviolet region Both involve excitation of an electron to an antibonding tt orbital In one called a TT TT transition the electron is one of the tt electrons of the C=0 group In the other called an n ir transition it is one of the oxygen lone pair electrons Because the tt electrons are more strongly held than the lone parr electrons the transition is of... 

A further interesting feature of the gallium phosphides and arsenides is that the former compounds are colorless whereas the latter range from yellow to orange. Color can arise from ir- ir transitions in main group compounds for example, in the disilylenes and digermenes R2E = ER2 (E = Si, Ge) in which the it- tt transitions occur at lower energy than... 

In carbonyls and heterocycles possessing both n-> tt and 77 - 77 excited states one would expect S - T n. transitions to be 102-103 times more efficient than S -> T . transitions/1425 We saw in Section 5.6a that the contribution of the overlap integral (J X1X2 dTo) in the transition probability is greater for transitions occurring between states of different type (n, 77 77,77 ) than for transitions between states of the same type (ir, tt -n,... 

The characteristic features of the UV and IR spectra of 43 unsaturated 4/f-pyrido[l,2-a]pyrimidin-4-ones 22 were systematically studied. The negative solvent effect of the lowest-energy tt-tt transition was investigated by the PPP quantum-chemical method (85JHC481). 

Bovine ROS membranes show a CD band at ca. 280 nm attributed to tt-tt transitions of aromatic residues and n-ir transitions of cysteine, as well as two maxima in the visible region at ca. 340 nm and 490 nm (the / and a bands) corresponding to the cis and main peaks of the absorption spectrum. The intensity of the a band in the CD is species-dependent, but is always somewhat blue-shifted relative to the Xmax in all species, and this shift is promoted by detergent solubilization. Strong micellar effects have been observed in the intensity of both a and / CD bands [44] (Fig. 4). 

Two other copper complexes, mononnclear [Cn(acac)(phen)(H20)]C104 and onedimensional polynuclear [Cu(acac)(bipy)(C104)] , have square-pyramidal structure. The latter complex has fragments bridged by perchlorate anions resulting in nentral polynn-clear chains. The solid-state spectra exhibit a broad d-d band and intraligand tt-tt transitions. IR data show that C—O vibrations correspond to a very strong intensity band at 1585 cm , as well as 1578 and 1525 cm . ... 

Spectral Properties. The spectral properties of PVTMSK have an important bearing on the lithographic utility and behavior of this polymer. The IR and UV spectra of solid films of PVTMSK have already been discussed in some detail in our previous paper (11) thus only the salient points will be presented in this chapter. The most characteristic feature in the UV spectrum of PVTMSK is a long-wavelength electronic transition with a maximum at 365 nm (Figure 4). This n — tt transition (19) provides the basis for the photosensitivity of PVTMSK to mid-UV radiation. 

Preparations of tris-bipyridyl (156, 519) and tris-phenanthroline indium(III) complexes have been described. The d<- d bands fall in the region of the ligand tt <-> tt transitions. The luminescence spectra of the cations are considered to arise from n d transitions (739). Cis-[Ir(phen)2Cl2]Cl is known (156) and has been resolved (104). However, the complex originally claimed as irans-[Ir(phen).2Cl2]Cl-3H20 (156) and shown to react with hydrochloric acid (452) is, in fact, (phen H+)[Ir(phen)Cl4] (104). The compounds [Ir(phen)2X.2]+ [Ir(phen)X4] are known (X = Cl, Br, or I) and the cations probably have cis configurations. 

Kamlet, JACS 88, 4761 (1966) Trichloronitromethane. This article supplements the material in Vol 3, C256-R under Chloroform and Derivatives CA Registry No 76-06-2. The IR spectrum and assignment of peaks are given in Ref 2 and in the UV there is a n TT transition at 35907cm" (Ref 3). 

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