Recently synthesized porphyrin-fullerene dyads with two separate linkers form a nearly symmetric complex with π-stack sandwich-like structure. The interchromophore interactions of such complexes can be finetuned by varying the linker lengths, which opens an opportunity to control physical and chemical properties of the dyads. Absorption spectroscopy emerged as a convenient means to register the interchromophore interactions: the spectra of the chromophores ground-state absorptions show appreciable perturbations and, more importantly, an additional absorption feature is discernible in the near-infrared region. Similarly, the emission spectra have a character typical for intramolecular exciplex. These new spectral features (i.e., absorption and emission) were attributed to a new electronic state, namely, an intramolecular preformed exciplex, featuring a common molecular orbital with a partial charge transfer (CT) character. From the mechanistic point of view, it is important that the preformed exciplex preceded the actual nonemitting charge separated (CS) state. The quantitative analysis of the CT absorption and the exciplex emission bands within the framework of the Marcus electron transfer (ET) theory allowed us to estimate the energy of the exciplex, ∆G°, the solvent or outer-sphere reorganization energy, λ s , the internal reorganization energy, λ V , the energy of the vibrational mode, E V , and the electronic coupling matrix element, V. Variation in the linker lengths shows that mainly the electronic coupling is affected by this structural modification, leaving the other parameters essentially unchanged. The strongest coupling, V ) 450 cm -1 (0.056 eV), was observed for the dioxyethyl type of linkers, whereas in the shorter, oxymethyl type, and longer, dioxypropyl type, dyads the couplings were much weaker (190 and 270 cm -1 , respectively). Photodynamics of the dyads was studied in the femtoand picosecond time domains, using the emission up-conversion and absorption pump-probe techniques.

A series of electron donor−acceptor (DA) dyads, composed of a porphyrin donor and a fullerene acceptor covalently linked with two molecular chains, were used to fabricate solid molecular films with the Langmuir−Blodgett (LB) technique. By means of the LB technique, the DA molecules can be oriented perpendicular to the plane of the substrate. In DHD6ee and its zinc derivative hydrophilic groups are attached to the phenyl moieties in the porphyrin end of the molecule; while in the other three dyads, TBD6a, TBD6hp, and TBD4hp, the hydrophilic groups are in the fullerene end of the molecule. This makes it possible to alternate the orientation of the molecules in two opposite directions with respect to the air−water interface and to fabricate molecular assemblies in which the direction of the primary photoinduced vectorial electron transfer can be controlled both by the deposition direction of the LB monolayer and by the selection of the used DA molecule. This was proved by the time-resolved Maxwell displacement charge measurements. The spectroscopic properties of the DA films were studied with the steady-state absorption and fluorescence methods. In addition, the time correlated single photon counting technique was used to determine the fluorescence properties of the dyad films.

1,7- And 1,6-regioisomers of N,N′-dioctyl-di(2,4-di-tert-butylphenoxy)perylene diimide (1,7-5 and 1,6-5) and N,N′-dioctyl-dipyrrolidinylperylene diimide (1,7-8 and 1,6-8) dyes are prepared. These 1,7- and 1,6-regioisomers are successfully isolated from the regioisomeric mixture using conventional methods of separation and subsequently characterized, unambiguously, by 300 MHz 1H NMR spectroscopy. This is the very first time when 1,6-regioisomers of diphenoxy and dipyrrolidinyl substituted perylene diimides are obtained in pure form. Optical and redox properties of these 1,6-regioisomers are examined extensively and compared with respective 1,7-regioiosmers. The optical and electrochemical characteristics of diphenoxy substituted isomers, 1,7-5 and 1,6-5, were found to be virtually the same. However, quite unexpectedly, crucial differences were observed in the properties of regioisomers of dipyrrolidinyl substituted PDIs, 1,7-8 and 1,6-8. Differential pulse voltammetry revealed that 1,7-8 has better electron-donating ability compare to that of 1,6-8. Pronounced differences were observed in the optical properties too. In addition to the lowest energy absorption band at around 700 nm, 1,6-8 exhibits another strong absorption band at ca. 560 nm, and consequently, covers larger part of the visible region relative to that of 1,7-8. Steady-state emission and fluorescence lifetime studies, carried out in solvents of different polarities, revealed that regioisomer 1,6-8 has inherently lower fluorescence quantum yields and lifetimes compared to that of 1,7-8. This fundamental information on the redox and optical properties of 1,6- and 1,7-regioisomers of diphenoxy and dipyrrolidinyl substituted PDIs will be of value especially for material chemists to develop more efficient systems and devices from bay-functionalized perylene diimides.

Photoinduced processes in phthalocyanine-functionalized gold nanoparticles (Pc-AuNPs) have been investigated by spectroscopic measurements. The metal-free phthalocyanines used have two linkers with thioacetate groups for bonding to the gold nanoparticle surface, and the attachment was achieved using a ligand exchange reaction. The absorption spectrum of the Pc-AuNPs shows a broadening of the phthalocyanine Q-band absorption, probably due to a tight packing of the phthalocyanines on the gold nanoparticle surface. For the attached phthalocyanines, fluorescence is strongly quenched, and the fluorescence lifetimes determined by time-correlated single photon counting (TCSPC) are strongly reduced. The quenching mechanisms were studied in detail with time-resolved absorption (pump−probe) measurements. A selective excitation of the gold cores in the pump−probe experiment results in an energy transfer from the gold nanoparticles to the attached phthalocyanines in ∼2.4 ps. Photoexcitation of mainly the phthalocyanines in the functionalized nanoparticles leads to an electron transfer to the gold core in ∼3.0 ps. The recombination of charges in the Pc-AuNP takes place on a picosecond time scale. In addition, there is evidence of energy transfer from the photoexcited phthalocyanines to the gold nanoparticles.