EXCITED-STATE DYNAMICS OF ANTHRAQUINONES AND ELECTRON-TRANSFER FROM GROUND-STATE TRIETHYLAMINE TO THE 2ND AND OR LOWEST EXCITED TRIPLET-STATES OF ANTHRAQUINONES

Picosecond laser photolysis of 1,8-dibromoanthraquinone (1,8-DBAQ) and 1,8-dichloroanthraquinone (1,8-DCAQ) in solutions at room temperature: has revealed the existence of the second excited n-pi-* triplet [T2(n-pi-*)] states with a localized charge-transfer character between the halogen and oxygen atoms. The internal conversion (IC) times from the T2(n-pi-*) states to the lowest excited pi-pi* triplet [T1(pi-pi-*)] states are 70-110 ps for 1,8-DBAQ and 700-750 ps for 1,8-DCAQ. In toluene and ethanol, an electron transfer from ground-state triethylamine (TEA) to triplet XAQ (anthraquinone and halogenoanthraquinones) forming the exciplexes [3(XAQ - TEA)*] has been found to occur via the T1 states of XAQ; these 3(XAQ - TEA)* change to the contact ion pairs between the XAQ radical anions (XAQ-) and the TEA radical cation. Neither free XAQ- nor 3(XAQ - TEA)* are produced via the T2 states of XAQ in toluene and ethanol. In acetonitrile, however, free XAQ- and 3(XAQ - TEA)* or the ion pairs (or the contact ion pairs) are produced via the T2 and T1 states of XAQ, respectively.