The fluorescence of a designed water-soluble 4-sulfonato-1,8-naphthalimide dye can be switched on by the synchronous host-guest complexation with cucurbit[7]uril and decrease in pH (from 9 to 7). This affords a dual resettable (by addition of cadaverine as competitor or by deprotonation) logic gate based on modulation of photoinduced electron transfer.

Photochromic spiropyrans modified with fluorophores were investigated as molecular platforms for the achievement of fluorescence switching through modulation of energy transfer. The dyads were designed in such a way that energy transfer is only observed for the open forms of the photochrome (merocyanine and protonated merocyanine), whereas the closed spiropyran is inactive as an energy acceptor. This was made possible through a deliberate choice of fluorophores (4-amino-1,8-naphthalimide, dansyl, and perylene) that produce zero spectral overlap with the spiro form and considerable overlap for the merocyanine forms. From the Förster theory, energy transfer is predicted to be highly efficient and in some cases of 100% efficiency. The combined switching by photonic (light of λ>530 nm) and chemical (base) inputs enabled the creation of a sequential logic device, which is the basic element of a keypad lock. Furthermore, in combination with an anthracene-based acidochromic fluorescence switch, a reversible logic device was designed. This enables the unambiguous coding of different input combinations through multicolour fluorescence signalling. All devices can be conveniently reset to their initial states and repeatedly cycled.

A fluorophore 1 -spacer-receptor-spacer-fluorophore 2 dyad was prepared and photophysically characterized. The two spectrally well-differentiated fluorophores are 1,8-naphthalimide and its 4-amino-substituted derivative, the latter showing strong ICT emission. The receptor unit consists of a tertiary amine, which leads to siteselective PET (only the 1,8-naphthalimide part gets quenched). This process can be blocked by protonation of the tertiary amine, which, on the other hand, results in enhanced singlet-singlet energy transfer between the 1,8-naphthalimide and 4-amino-1,8-naphthalimide parts (Φ EET ) 0.27 and 0.59 for neutral and monoprotonated form, respectively). In acetonitrile, the monoprotonated form can be deprotonated by sufficiently basic anions like fluoride in micromolar concentration (<20 µM). The observed fluorescence quenching, due to PET-reactivation, is ca. 41%. Further addition of fluoride in concentrations >1 mM leads to deprotonation of the 4-amino group of one of the naphthalimides, which is accompanied by more fluorescence quenching (ca. 93%). The resulting double-sigmoidal titration curve enables the implementation of ternary logic. Using fluoride anions as degenerate inputs results in a ternary NOR logic gate, which is demonstrated for the first time.

The photochromic fluorescence switching of a fulgimide derivative was used to implement the first molecule-based D (delay) flip-flop device, which works based on the principles of sequential logic. The device operates exclusively with photonic signals and can be conveniently switched in repeated cycles.

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A new approach towards the rapid identification of quality binders to cucurbiturils--those that combine high affinity with high selectivity for a particular homologue--was developed. The assay exploits macrocycle-specific optical fingerprints (colorimetric or fluorimetric) of carefully selected indicators dyes. The screening of a guest library revealed known (e.g., adamantane derivatives) and new (e.g., terpenes) quality binders. The predictive power of the assay was underpinned by the modeling of the involved thermodynamic equilibria.

A novel molecular system with characteristics of an OFF-ON-OFF fluorescence switch was designed to integrate the function of a T-latch. In detail, a receptor1-fluorophore-receptor2 architecture was adopted to achieve fluorescence switching upon addition of protons.

Aminonaphthalimide-BODIPY energy transfer cassettes were found to show very fast (kEET ≈ 10(10)-10(11) s(-1) and efficient BODIPY fluorescence sensitization. This was observed upon one- and two-photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison with the direct excitation of the BODIPY chromophore, the two-photon absorption cross-section δ of the dyads is significantly incremented by the presence of the aminonaphthalimide donor [δ ≈ 10 GM for the BODIPY versus 19-26 GM in the dyad at λ(exc)=840 nm; 1 GM (Goeppert-Mayer unit)=10(-50) cm(4) smolecule(-1) photon-(1)]. The electronic decoupling of the donor and acceptor, which is a precondition for the energy transfercassette concept, was demonstrated by time-dependent density functional theory calculations. The applicability of the new probes in the one- and twophoton excitation mode was demonstrated in a proof-of-principle approach in the fluorescence imaging of HeLa cells. To the best of our knowledge, this is the first demonstration of the merging of multiphoton excitation with the energy transfer cassette concept for a BODIPY-containing dyad.