Si. Druzhinin et al., THE EFFECT OF AMINO GROUP-STRUCTURE ON EXCITED-STATE PROTONATION OF 7-AMINOCOUMARINS, High energy chemistry, 29(1), 1995, pp. 48-51
The reaction of proton transfer in the excited states of aminocoumarin
s with primary (Ia and If), secondary (Ib and Ic), and tertiary (Id, I
e, IIa; and IIb) 7-amino groups was studied. Unlike the case of 7-amin
ocoumarins Ia - Ic and IIb, the limiting (acid concentration --> infin
ity) fluorescence quantum yield phi(infinity)' of the photoprotonation
product of 7-aminocoumarins Id and Ie with the unfixed tertiary amino
group is abnormally low in polar (ethanol or dimethylsulfoxide) solve
nts. A decrease in polarity of the medium leads to a considerable (by
a factor of > 40 in cyclohexane) increase in phi(infinity)'. This incr
ease in the quantum yield is due to a decrease in the formation rate o
f the twisted intramolecular charge-transfer state that does not exhib
it fluorescence.