The radical anions of aromatic diimides have been implicated recently in a wide variety of photochemical electron transfer reactions. Photoexcitation of these radical anions produces powerfully reducing species. Yet, the properties of the π* excited doublet states of these organic radical anions remain obscure. The radical anions of three aromatic imides with increasingly larger π systems, N-(2,5-di-tert-butylphenyl)phthalimide, 1, N-(2,5-di-tert-butylphenyl)-1,8-naphthalimide, 2, and N-(2,5-di-tert-butylphenyl)perylene-3,4-dicarboximide, 3, as well as the three corresponding aromatic diimides, N,N ‘-bis(2,5-di-tert-butylphenyl)pyromellitimide, 4a, N,N ‘-bis(2,5-di-tert-butylphenyl)-naphthalene-1,8:4,5-tetracarboxydiimide, 5a, and N,N ‘ -bis(2,5-di-tert-butylphenyl)perylene-3,4:9,10-tetracarboxydiimide, 6, were produced by electrochemical reduction of the neutral molecules in an optically transparent thin layer electrochemical cell. The radical anions of these imides and diimides all exhibit intense visible and weaker near-IR absorption bands corresponding to their D0 → D n transitions. Excited states of the radical anions were generated by subpicosecond excitation into these absorption bands. Excitation of 1 •- and 2 •- resulted in decomposition of these radical anions, whereas excitation of 3 •-−6 •- yielded transient spectra of their D1 → D n transitions and the lifetimes of D1. The lifetimes of the D1 excited states of the radical anions of 3 •-−6 •- are all less than 600 ps and increase as the D0−D1 energy gap increases. These results impose design constraints on the use of these excited radical anions as electron donors in electron-transfer systems targeted toward molecular electronics and solar energy conversion.

The spectroscopic properties and dynamics of the lowest excited singlet states of peridinin, fucoxanthin, neoxanthin, uriolide acetate, spheroidene, and spheroidenone in several different solvents have been studied by steady-state absorption and fast-transient optical spectroscopic techniques. Peridinin, fucoxanthin, uriolide acetate, and spheroidenone, which contain carbonyl functional groups in conjugation with the carbon-carbon π-electron system, display broader absorption spectral features and are affected more by the solvent environment than neoxanthin and spheroidene, which do not contain carbonyl functional groups. The possible sources of the spectral broadening are explored by examining the absorption spectra at 77 K in glassy solvents. Also, carotenoids which contain carbonyls have complex transient absorption spectra and show a pronounced dependence of the excited singlet state lifetime on the solvent environment. It is postulated that these effects are related to the presence of an intramolecular charge transfer state strongly coupled to the S 1 (2 1 A g ) excited singlet state. Structural variations in the series of carotenoids studied here make it possible to focus on the general molecular features that control the spectroscopic and dynamic properties of carotenoids.