Lowest excited triplet state

Nanosecond flash photolysis of 1,4-dinitro-naphthalene in aerated and deaerated solvents showed a transient species with absorption maximum at 545nm. The maximum of the transient absorption was independent of solvent polarity and its lifetime seemed to be a function of the hydrogen donor efficiency of the solvent. The transient absorption was attributed to the lowest excited triplet state of 1,4-dinitronaphthalene. Based on spectroscopic and kinetic evidence, the triplet state of 1,4-dinitronaphthalene behaved as an n - Tt state in nonpolar solvents,... 

Differences in reactivity toward photoreduction result from differences in the character of the lowest excited triplet state. 

This suggests that (66) is formed from the a,/3-unsaturated ketone excited singlet and (67) is formed from the lowest excited triplet state. 

The overall process of ()2 quenching simply converts the excess energy of singlet oxygen to heat via the carotenoid [CAR] lowest excited triplet state [3CAR],... 

If chemiluminescence is to occur, a critical electron-transfer enthalpy value must be exceeded. This value is similar to the energy of the lowest excited triplet state, as was found in the case of fluoranthene 150>, for example. 

Pulse radiolysis is used also for preparation of excited states of dienes and polyenes. This is done by irradiation of the diene/polyene in toluene solution. The radiolysis of toluene yield high concentration of molecules in the triplet excited state of the solute. Wilbrandt and coworkers61 pulse-radiolysed 1 mM solution of al I -lrans-1,3,5-heptatriene in toluene solution and observed the absorption spectra of the triplet state of the heptatriene with a maximum at 315 nm. The same group62 produced and measured the absorption spectra of several isomeric retinals in their lowest excited triplet state by pulse irradiation of their dilute solution in Ar-saturated benzene containing 10 2 M naphthalene. Nakabayashi and coworkers63 prepared the lowest triplet states of 1,3-cyclohexadiene,... 

Phosphorescence Photon emission. Phosphorescence involves a spin-forbidden radiative transition between states of different multiplicity, usually from the lowest vibrational level of the lowest excited triplet state, Tt. Ti(v = 0) - S0 + hv... 

Protonation of (n, 7t )-nitrobenzene had been suggested earlier and later questioned I8) on account of an estimated extremely weak basicity of 3(n, tt )-nitrobenzene. Enhanced basicity of the lowest excited singlet state compared to ground and lowest excited triplet state has been derived from shifts in the phosphorescence and absorption spectra of nitrophenols ). On this basis, the increased rate of nitrobenzene photoreduction in acidic solution is formd to be thermodynamically unfeasible in the lowest excited triplet state >. Although it might be thermodynamically feasible in the excited singlet state, the short lifetime of the latter state may make this possibility unlikely. 

A (n,T )-configuration has been assigned to the lowest excited triplet state Et 52 kcal mole ) of 4-nitropyridine-1-oxide from both phosphorescence and S—T absorption studies... 

The lowest excited triplet states of a-dicarbonyl compounds are considerably less energetic than those of simple carbonyls. For instance the energy of the vibrationally relaxed triplet of glyoxal is 55 kcal,366 as compared to 72 kcal for formaldehyde. Irradiation of glyoxal at 4358 A populates the lowest vibrational levels of the first excited singlet, 30% of which fluoresce and 70% of which cross over to the triplet manifold.388 Almost all of the triplet molecules then decompose to formaldehyde and carbon monoxide, the phosphorescence yield being only 0.1%. 

The photochemical and photobiological behaviour of coumarins is well documented. It is considered that the lowest excited triplet state plays an important role in such processes and information about the nature of the Ti state of coumarin has been derived from magnetic and spectroscopic studies (76JA3460). 

The lowest excited triplet state in anthryl-oligothiophenes (634) were studied (96CPL(260)125). Also, binaphthyl oligothiophenes have been studied (09MM1710). The triplet state properties are studied with respect to coupling effects between the molecular subunits for a different chain length n and also for additional pyridine substitution (635). 

In all cases, the cyclic amino substituent in the major diastereoisomer is oriented cis to the aryl moiety of the participating aroyl group whereas the nonparticipating aroyl group is cis to the nitrile function. Whereas 2-naphthyl-substituted diones from oxetanes, 1,1 -naphthyl- and 1-(1-naphthyl)-2-phenyl ethanedione are unreactive. The latter effect probably reflects the nn nature of the lowest excited triplet state of these diones. 

In a large molecule the vibrational and rotational levels associated with any electronic state become so extremely congested at high vibrational energies that they form a pseudocontinuum. This is illustrated for S0,5) and the lowest excited triplet state 7), lying below Sh... 

The ESR spectra of the lowest excited triplet states of several naphthyridines in ethanol glasses and stretched polyvinyl alcohol films at 77 K have been determined <87JMR(7l)303>. A comparison of the calculated and experimental ESR spectral hyperfine coupling of radical anions has been reported <83ZN(A)415>. 

The effect of temperature on the PL spectra is important as regards the internal conversion between the lowest excited triplet state and the ground state, because of the longer lifetimes of triplet states (Anpo and Che, 1999). 

Jablonski" diagram, showing, for a molecule in the ground (spin)-singlet state S0, the (induced) absorptions, a double-quantum transition, (spontaneous) fluorescence, (spontaneous) phosphorescence, internal conversion, and intersystem crossing between the singlet manifold of states S0, S1 S2, and S3, and the lowest excited triplet state T-. ... 

Molecular nitrogen, N2, is one of the most extensively studied diatomic molecules and optical spectroscopy has provided a wealth of information about its ground and excited electronic states. Molecular beam magnetic resonance studies of N2 in its ground state have yielded information about 14N nuclear spin dipolar and quadrupole interactions. Similar studies of N2 in its electronically excited A 3LU state were described in two very extensive papers by Freund, Miller, De Santis and Lurio [43] (paper I) and De Santis, Lurio, Miller and Freund [44] (paper II). We will describe their results and analysis in detail, but first note in passing that, strictly speaking, the lowest excited triplet state should be labelled the a state the label A has been used by all concerned in the past, so we will continue to do so. 

Infrared and Resonance Raman Spectroscopy. Reviewson the uses of resonance Raman spectroscopy in biochemistry and biology include sections on carotenoproteins, visual pigments, and bacteriorhodopsin. The resonance Raman spectrum of the lowest excited triplet state of /3-carotene has been reported.A resonance Raman method has been used for the quantitative analysis of /3-carotene and lutein (20) in tobacco.The mechanism of carotenoid-protein interactions in the carotenoproteins ovoverdin and /3-crustacyanin has been investigated by resonance Raman spectroscopy. " 2 axanthin (24) has been used as a resonance Raman probe of membrane structure. " The resonance Raman spectra have been reported of all-frans-anhydrovitamin A (194), " /3-ionone, retinals, and Schiff bases.The technique has been used extensively to study... 

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