Wavelength converting/shifting

An OH group affects the UV VIS spectrum of benzene m a way similar to that of an NH2 group but to a smaller extent In basic solution m which OH is converted to 0 however the shift to longer wavelengths exceeds that of an NH2 group... 

In the laboratory 254 has inter alia been obtained in an argon matrix by irradiation of diazopropyne (253) at 10 K [106], Matrix isolation ESR and IR studies and ab initio calculations show it to be a 1,3-diradical with C2 symmetry, as indicated in Scheme 5.39 [107]. Irradiation with shorter wavelength light induces a 1,3-hydrogen shift by which the triplet propynylidene 254 is converted into the singlet propadienyli-dene 255, the parent system of unsaturated carbenes such as 251 (Scheme 5.39) [108]. 

In variance with its wavelength independency at 77°K, at room temperature Msc appears to decrease when blue shifting Aexc within the range of the main band (172). This observation was explained by suggesting that certain molecular conformations, achievable at 300°K (but not at 77°K) within less than 35 ps, may very efficiently convert to the ground state (172). That internal conversion to the ground state competes with population of the state [l(n, it ) or 1(tt, tt ), Mg] from which ISC takes place was also suggested by Bensasson et al. to account for the decrease in 4>igc when Aexc is varied from 353 nm (within band I) to 265 nm (within band III) (168,170). 

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