The coordination compound Fe(BM-4-PTP)2(NCS)2⋅2MeOH (1) including the photoisomerizable ligand BM-4-PTP (1,2-bis(2′-methyl-5′-(pyrid-4″-yl)thien-3′-yl)perfluorocyclopentene) was obtained as an orange powder. The powder turns blue upon photocyclization of the 1,2-bisthienyl photochromic ligand induced by UV light irradiation at room temperature. Photocycloreversion is obtained by visible light irradiation of the material in the solid state. The orange and blue powders were investigated over the temperature range (5–293K) and pressure range (1bar–12kbar) by magnetic susceptibility measurements and variable temperature 57Fe Mössbauer spectroscopy. The photo-induced colour change is accompanied by a distinct magnetic variation at room temperature. Potentialities of this functional optical material for display and data recording are introduced.

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4-(Dimethylamino)-4'-cyano-1,4-diphenylbutadiene (DCB) and 4-(dimethylamino)-2,6-dimethyl-4'-cyano-1,4-diphenylbutadiene (DMDCB) have been characterized spectroscopically. Quantum chemical calculations were performed for comparison. Solvatochromic shifts of the fluorescence were strong and showed a linear dependence on the solvent polarity parameters, whereas shifts in the absorption spectra are very weak only correlate better with the polarizability of the solvents. Excited state dipole moments derived from fluorescence using the Onsager model are very large and similar for both compounds. It is concluded that a strongly allowed and highly dipolar pi, pi* state is the lowest excited state in polar solvents. The strong difference in absorption and fluorescence solvatochromic slopes suggests that the simple Onsager model with a point dipole approximation is not sufficient here.

4-Dimethylamino-4′-cyano-1,4-diphenylbutadiene (DCB) and 4-dimethylamino-2,6-dimethyl-4′-cyano-1,4-diphenylbutadiene (DMDCB) have been photophysically characterized. Quantum chemical calculations were performed for comparison. The fluorescence quantum yields increase with increasing solvent polarity and decreasing temperature. It is concluded that the lowest excited state is a strongly allowed and highly dipolar π,π* state in polar solvents, and nonradiative deactivation is reduced. This occurs similarly in both compounds. More specifically, the two methyl groups in DMDCB do not enhance the nonradiative decay. This suggests that neither a fluorescent nor a nonfluorescent TICT state is involved in DCB and DMDCB.

Pyrrolobenzenes, with different linking and substitution patterns, 2′-(4-cyanophenyl)-methylpyrrole (MP2-BN) and 2′-(2,5-cyanophenyl)-methylpyrrole (MP2-B25CN), are investigated by steady-state and time-resolved UV–Vis spectroscopy and compared to the parent compound N-pyrrolobenzonitrile (PBN). Both the electron donor–acceptor linking sites and the strength of the electron acceptor moiety are found to influence the emission characteristics of these compounds. The large radiative rate constant of MP2-BN indicates an allowed emission due to mesomeric interaction between the donor and acceptor moieties (MICT), whereas in the case of PBN and MP2-B25CN, the reduced radiative rate constant indicates a forbidden emission from a twisted intramolecular charge transfer (TICT) state.

Amino-diphenylanilines and their planarized and twisted model compounds have been investigated by steady state and time-resolved absorption and emission, as well as by spectroelectrochemistry. These polyaniline model compounds show that the observation of excited states with full charge separation is linked to molecular twisting where the diaminobenzene is the donor and the phenyl group the acceptor. The observable charge transfer fluorescence shows the characteristic features of twisted intramolecular charge transfer (TICT) excited states, i.e. forbidden emissive properties and strong solvatochromic red shift. The transient absorption spectrum of the TICT state matches the ground state absorption spectrum of the electrochemically produced radical cation of the molecule. This is the first example where excited-state properties of the neutral and ground state properties of the radical cation are directly linked.

p-(N, N-Dimethylamino)benzenesulfonamide (DMABSA), a dual fluorescent fluorophore, has been derivatized into two new fluoroionophores for transition metal cations. The electron-acceptor sulfonamide group has been N-substituted by a 2-pyridylmethylene group to lead to a bidentate ligand which forms a 2:1 complex with Cu(ii). The crystal structure of the copper(ii) complex is reported. The Cu(ii) is coordinated through the pyridine N- and sulfonamide N-deprotonated atom which account for the blue-shift of the absorption and the partly quenched fluorescence. When DMABSA was incorporated into the tris(2-aminoethyl)amine (tren), a tripodal, dual-fluorescent ligand, is obtained which shows higher binding affinity for Zn(ii) than for Cu(ii). Furthermore, the large increase of the short wavelength emission and the disappearance of the TICT emission, upon Zn complexation, allow measurements of the Zn(ii) concentration from relative fluorescence intensity at two wavelengths.

A novel oxidative photodehydrocyclization of indolinylphenylethenes to a polycyclic heteroaromatic cation with good yields was described. Starting from the trans derivative, the phototransformation is a multistep process. The process includes two photochemical reactions and a trans-cis isomerization reaction, followed by an 1-aza-1,3,5-hexatrienic electrocyclic reaction involving the formation of a C-N bond. The cyclized product gives the stable heteroaromatic cations from hydride elimination with oxygen from air or iodine.

Low temperature dual fluorescence of several derivatives of 4-aminodiphenylamine is investigated quantitatively. A strong thermochromic and solvatochromic redshift is indicative of the high dipole moment of the CT state emitting at long wavelength. The combination of steady state and time-resolved data allowed the calculation of the excited-state equilibrium. The absence of CT-risetimes in diethyl ether and their presence in butyronitrile points to the complication by additional ground state conformational equilibria. Both ground and excited state equilibria depend on solvent polarity and temperature. High solvent polarity favours one of the ground state conformers.

A photochromic dithienylethene, bearing a phenyl azacrown as an ionophore and a formyl group as an electron-accepting substituent, changes its binding ability for Ca2+ by a factor higher than 103 by photoirradiation. This new photoionochromic displays a wavelength-dependent competition between fluorescence and photocyclization assigned to a red-shifted absorption of the fluorescing conformer compared to the absorption of the photoreactive conformer.

Starting from the pentafluorophenyl ester of 4-(dimethylamino)benzoic acid, two dual fluorescent amide ligands with aza-15-crown-5 and 2-(aminomethyl)pyridine were obtained for sensing, respectively, alkali (alkaline-earth) and transition (heavy) metal cations. The crystal structure of the coppers II complex is reported. The Cu2+ is coordinated through the pyridine N- and amide O-atoms of two symmetry-related ligands. The azacrown-directed Ca-chelation to the N-atom of the amide leads to a slight quenching of the two fluorescence bands, In contrast, the pyridine directed Cull-chelation to the O-atom of the amide enhances the short-wavelength emission 17-fold over the locally excited state (LE), quenching the twisted intramolecular kcharge-transfer (TICT) emission. and, as a result, the intensity ratio I(LE)//(TICT) provides an accurate and sensitive measurement of the Cu-II concentration. These different cation effects are dependent on which atom (N vs. O) of the amide function participates in cation coordination: while the Ca2+ interaction with the N-atom electron pair leads to the deconjugation of the amide N-atom from the fluorophore, Cu2+ interaction with the lone pair of the O-atom of the carbonyl group increases the energy of the n-pi* but also of the L-1(a) transition and therefore close the channel to the TICT state.

The use of metal-organic complexes is a potentially fruitful approach for the development of novel enzyme inhibitors. They hold the attractive promise of forming stronger attachments with the target by combining the co-ordination ability of metals with the unique stereoelectronic properties of the ligand. We demonstrated that this approach can be successfully used to inhibit the protease of the human immunodeficiency virus (type 1). Several ligands bearing substituents designed to interact with the catalytic site of the enzyme when complexed to Cu2+ were synthesised. The inhibition pattern of the resulting copper(II) complexes was analysed. We showed that the copper(II) complex of N1-(4-methyl-2-pyridyl)-2,3,6-trimethoxybenzamide (C1) interacts with the active site of the enzyme leading to competitive inhibition. On the other hand, N2-pyridine-amide ligands and oxazinane carboxamide ligand were found to be poor chelators of the cupric ion under the enzymatic assay conditions. In these cases, the observed inhibition was attributed to released cupric ions which react with cysteine residues on the surface of the protease. While unchelated metal cations are not likely to be useful agents, metal chelates such as C1 should be considered as promising lead compounds for the development of targeted drugs.

The preparation of new 25,27-bis(alkyloxy)calix[4]arenes-crown-6 in the cone, partial-cone and 1,3-alternate conformation is reported. We have also investigated the alkylation of the cone monoalkylated calix[4]arene-crown-6 achieved using Cs2CO3. This reaction afforded a mixture of cone and partial-cone calix[4]arenes-crown-6 having an alkyl. chain anti or syn to the polyether ring. Conformations have been probed using H-1, C-13, 2D-NMR and NOESY analysis, and using X-ray crystallography. Extraction experiments using a two-phase solvent method involving cesium picrate were performed for these newly synthesized conformers. They reveal and confirm the strong preference for the 1,3-alternate conformers. The affinity of 1,3-alternate calixarenes for Cs+ has been assessed by complexation measurements (log,8) using a spectrophotometric technique. No significant Cs+ extraction difference was observed in relation to the nature of the alkyl chains on the aromatic rings. H-1 NMR studies of the 1,3-alternate calixarene Cs+ complexes confirms the cation's spacial position between the two aromatic rings, due to cation-pi interactions.

Integrated supramolecular systems with a receptor built in a photo- or electroactive unit have been reviewed with the focus on their particular electronic properties and different photochemical and electrochemical processes which make them suitable for cation sensing or switching. The fluoroionophores with an electron donating ionophore have been the most investigated and their initial weakness related to cation decoordination in the excited state. The small blue-shift of the fluorescence spectrum and the slight change of the emission quantum yield upon cation complexation, have now been overcome by a careful combination of several donor and acceptor units, which provide new low-lying excited states decoupled from the complexed ionophore and by using TICT probes where the electronic coupling between the D and A parts is too small to induce decoordination of the cation during the excited state lifetime. On the contrary the switching action requires that the binding ability of the ionophore be lowered or increased on a larger time scale. This has been done by electrochemical oxidation and by insertion of the ionophore into a photochromic system. Differences in binding ability of three to four orders of magnitude have been obtained and it is our belief that integrated supramolecular systems combining an ionophore and a photochromic moiety (photoionochromics) will be for cation switching as successfull as integrated fluoroionophores have been for sensing cations.

Intramolecular Charge Transfer (ICT) processes of 4-dimethylamino-4'-nitrostilbene (DNS) in solution are studied by pump-probe absorption spectroscopy with a 100 fs time resolution. The results are compared to transient CARS experiments. Pump-probe results confirm the formation of a radiative ICT state in low polar solvents. In a highly polar solvent (acetonitrile), the formation of a short-lived non-radiative ICT state is observed for the first time. CARS experiments support structural changes associated to ICT processes in highly polar solvents.

One of the classics in photochemistry, the photodimerization of anthracenes can be considered as a paradigm of the photocycloaddition of non saturated hydrocarbons. The historical steps of the mechanistic studies are reviewed: based on fluorescence quenching, cyclization quantum yields measurement, the influence of dioxygen and solvents, they support a singlet state pathway; the dimerization rate constants are found to be generally high for reactions occurring within a few nanoseconds unless they are slowed down or inhibited by steric strain. In several cases, excimers have been demonstrated to be intermediates and it is shown that excimer fluorescence and cyclization are competitive processes. Another intermediate known as pericyclic minimum (or conical intersection) is postulated to form a sort of floppy cycloadduct where the reacting centres are at mutual distances shorter than in excimers and longer than in dimers. For intermolecular dimerizations, the triplet state is also reactive but through triplet–triplet annihilation in dilute solutions. Intramolecular photocycloadditions have also been carefully examined, for the role of multiple excimer formation, regioselectivity (9,10∶1′,4′ and 9,10∶1′,2′ cyclization) and solvent polarity. The triplet state reactivity is shown to lead to 4π + 2π or 4π + 4π cycloadducts, depending on geometric factors. In the latter case when intersystem crossing is favoured by the substituents, cyclization quantum yields as high as 0.65–0.72 have been observed. Photodissociation quantum yields are generally high and the reactions are partly adiabatic, leading to excimer and monomer fluorescence, but the major part follows another pathway not fully elucidated by flash photolysis. Thermodynamic and kinetic parameters for the thermal cleavage are given; they reveal a large gamut of stability for the photocycloadducts.

The photophysical properties of several derivatives of 4-aminodiphenylamine (ADPA), model compounds of aniline dimers and trimers are investigated. Several compounds show dual fluorescence with a charge transfer (CT) component with a significantly reduced fluorescence rate constant which can be suppressed by bridging and enhanced by sterically hindering substituents, in close similarity to the compounds showing twisted intramolecular charge transfer (TICT). The relation to polyaniline (PANI) conductivity is also discussed.