We report here the synthesis and photophysical study of a series of electron donor–acceptor molecules, in which electron-donating 4-methoxyphenoxy groups are attached to the 1,7-bay positions of four different perylene tetracarboxylic acid derivatives, namely, perylene tetraesters 1, perylene monoimide diesters 2, perylene bisimides 3, and perylene monobenzimidazole monoimides 4. These perylene derivatives are used because of their increasing order of electron-accepting capability upon moving from 1 to 4. Two additional donor–acceptor molecules are synthesized by linking electron-donating 4-methoxyphenyl groups to the imide position of perylene monoimide diester 2 and perylene bisimide 3. The motivation for this study is to achieve a good control over the photoinduced charge-transfer (CT) process in perylene-based systems by altering the position of electron donors and tuning the electron deficiency of perylene core. A comprehensive study of the photophysical properties of these molecules has shown a highly systematic trend in the magnitude of CT as a function of increased electron deficiency of the perylene core and solvent polarity. Importantly, just by changing the attachment of electron-donating group from “bay” to “imide” position, we are able to block the CT process. This implies that the positioning of the electron donor at the perylene core strongly influences the kinetics of the photoinduced CT process. In these compounds, the CT process is characterized by the quenching of fluorescence and singlet excited-state lifetimes as compared to model compounds bearing non-electron-donating 4-tert-butylphenoxy groups. Transient absorption spectroscopy did not reveal spectra of CT states. This most likely implies that the CT state is not accumulated, because of the faster charge recombination.@en

Nucleophilic aromatic substitution reactions on 1,7-dibromoperylene-3,4,9,10-tetracarboxylic monoimide dibutylester, using phenol and pyrrolidine reagents, have been exploited to synthesize perylenes with four different substituents at the perylene core. The first substitution is always regiospecific at the imide-activated 7-position. A second substitution reaction does not always replace the bromine at C-1, but may replace a phenol substituent at the highly activated 7-position. Exploiting this reactivity pattern, a "mixed" 1,7-diphenoxy, 1,7-dipyrrolidinyl, and two 1-phenoxy-7-pyrrolidinyl derivatives have been synthesized.

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A family of novel unsymmetrical "peri"-substituted perylene-3,4,9,10-tetracarboxylic acid derivatives (5-10), with 1,6,7,12-tetrachloro-substituents at the bay-positions, has been synthesized. Subsequently, their redox and optical properties have been explored with the intent of unveiling opto-electronic characteristics of these newly synthesized compounds. To synthesize these new compounds, pure 1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxylic tetra-n-butylester (4) has been employed as the precursor and the structural modifications have been carried out exclusively at the "peri" positions in an efficient manner. The two synthons prepared in this work, 1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxylic di-n-butylester monoanhydride (5) and 1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxylic monoimide monoanhydride (8), are extremely valuable and versatile starting materials as they possess free anhydride functionality at the "peri" position in addition to the 1,6,7,12-tetrachloro-bay-substituents. Finally, the conventional methodology for the synthesis of 1,6,7,12-tetraphenoxy-bay-functionalized perylene bisimides and perylene bisbenzimidazoles has been modified to make it faster and more convenient.

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Perylene-3,4,9,10-tetracarboxylic tetraester-based fluorescent PET probes with aniline receptors attached either at the peri- or the bay-positions have been synthesized. By attaching aniline receptors at the bay position, pH-sensitive “light-up” probes, with fluorescence quantum yields ΦF > 0.75 and fluorescent enhancements FE > 500 in ethanol, have been obtained. Graphical abstract: Fluorescent PET probes based on perylene-3,4,9,10-tetracarboxylic tetraesters @en