Assessing solvent effects on the singlet excited state lifetime of uracil derivatives: A femtosecond fluorescence upconversion study in alcohols and D2O

摘要: Abstract The excited state lifetimes of uracil, thymine and 5-fluorouracil have been measured using femtosecond UV fluorescence upconversion in various protic aprotic polar solvents. fastest decays are observed acetonitrile the slowest aqueous solution while those alcohols intermediate. No direct correlation with macroscopic solvent parameters such as polarity or viscosity is found, but hydrogen bonding one key factor affecting decay. It proposed that modulates relative energy two close-lying electronically states, bright ππ∗ dark nπ∗ states. This gap controls non-radiative relaxation through a conical intersection close to Franck–Condon region competing ultrafast internal conversion ground state. In addition, an inverse isotope effect D2O where faster than H2O.