Synthesis and Function of Photoactive Donor−Acceptor Systems of Bay-Functionalized Perylene Diimide Dyes in View of 1,7- and 1,6-Regioisomers

1,7- and 1,6-regioisomers of two important bay-functionalized perylene diimide dyes, namely N,N'-dioctyl-di(2,4-di-tert-butylphenoxy)perylene diimide and N,N'-dioctyl-dipyrrolidinylperylene diimide, have been synthesized, separated, and unambiguously characterized by 300 MHz 1H NMR. A detailed comparative study of their optical and electrochemical properties has been carried out, which revealed virtually the same characteristics of the 1,7- and 1,6-diphenoxy substituted perylene diimides. However, substantial differences have been observed in the properties of the two regioisomers of dipyrrolidinyl substituted PDIs. Subsequently, novel derivatives of dipyrrolidinyl functionalized perylene diimide, with additional substitution sites close to the perylene core, have been prepared by the bay-attachment of 2-(benzyloxymethyl)-pyrrolidine. During this, clear differences have been evidenced in the chemical behavior of the corresponding 1,7- and 1,6-regioisomers. The separated 1,7- and 1,6-derivatives have been utilized to prepare four perylene diimide−fullerene dyads, in which fullerene has been covalently linked to perylene diimide with one or two linkers. The differences in the excited-state dynamics of these 1,7- and 1,6-regioisomers have been studied. In contrast to previously reported perylene diimide−fullerene dyads, all the synthesized dyads have exhibited photoinduced electron transfer from the perylene diimide chromophore to fullerene, not only in a polar but also in a non-polar solvent. The electron transfer was found substantially faster and more efficient in the dyads containing 1,7-regioiosmer. A new series of donor−acceptor based ensembles, consisting of phenoxy or pyrrolidinyl functionalized perylene diimide covalently linked to Ru(II) polypyridine complex, has been synthesized and studied in detail by steady-state and time-resolved spectroscopy. In all the ensembles, the photoexcitation of either chromophore resulted in a long-lived triplet excited state of PDI (3PDI) as the final excited state, but the photochemical reactions leading to the triplet states were found to be essentially different for the two types of the ensembles. In the case of phenoxy-PDI based ensemble, the excitation of either chromophore leads to the electron transfer from the Ru(II) complex to PDI; whereas for the pyrrolidinyl-PDI based ensembles, the electron transfer is observed in opposite direction and only when the Ru(II) complex is excited. Finally, a dibenzo[a,c]phenazine molecule was coupled with fullerene to function as light-harvesting antenna in order to overcome poor absorption strength of fullerene in the visible spectral region. The suitability of the synthesized dibenzo[a,c]phenazine−fullerene dyad, for the photovoltaic applications, has been examined by detailed electrochemical and spectroscopic study