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Photo-induced electron transfer between a donor and acceptor subsystem in a molecule leads to an intramolecular chargetransfer (ICT) state. The ICT state of the molecule goes down to the ground state through various relaxation pathways. Among of them, in particular, the twisted intramolecular charge transfer (TICT) behavior has been a subject of interest to many photochemical researchers for years. 1The TICT model was firstly applied to explain the photophysical property of p-(N,Ndimethylamino)benzonitrile, indicating the dual fluorescence and the emission with a large Stokes shift in a polar solvent. 2,3 Since then, interpretation by the TICT model has been extended to other structurally related compounds showing anomalous dual fluorescence. Recently, the present authors demonstrated that N-phenyl-9-anthracenecarboxamide and N-phenyl-1-pyrenylcarboxamide derivatives show no fluorescence emission in solution through an ICT relaxation pathway similar to the TICT as the most plausible explanation. On the basis of this observation, we synthesized new fluorescent ionophores containing N-phenyl-9-anthracenecarboxamide 4 and N-phenyl-1-pyrenylcarboxamide 5 based on an ethyleneoxy chain, respectively. Upon complexing with metal ions, we could achieve the controlling TICT relaxation pathway with the "offon" fluorescent signal.These results inspired us to examine a photochemical property of naphthalene amides derivatives. Naphthalene is regarded as a strong tool for a highly sensitive detecting probe in fluoroionophores. 6 Kawakami et al. studied fluoroionophores containing naphthoic acid derivatives. 7-9The naphthyl alkyl amines were used as a photo-induced electron transfer (PET) detection moiety in the field of the molecular recognition chemistry. 10,11 Although many studies on naphthalene derivatives have been reported, spectroscopic observations about naphthylacetic aromatic amide are rather limited. In this communication, we demonstrate the photochemical behaviors of 14 and 15 (Fig. 1) upon the complexing with metal ions by means of fluorescence and NMR spectrometries. ExperimentalThe syntheses of 14 and 15 were carried out by the usual technique (Yield: 61.3% for 1, 58.3% for 2). 12,13 Their structures and purities were confirmed by the 1 H-NMR spectra and elemental analyses. Fluorescence spectra were measured by a Shimadzu RF-5300PC at 25˚C. The concentrations of fluorescent reagents were 5 × 10 -6 mol/dm 3 in purified acetonitrile. Alkaline earth metal cations were added into the solution of the fluorescent reagent as perchlorate salts. New fluorescent ionophores containing the 1-naphthylacetanilide moiety based on oligo-ethylene oxide (14 and 15) have been synthesized, and their photochemical behaviors have been studied. In the absence of a metal ion, the 1-naphthylacetanilide moiety showed a weak fluorescence emission (fluorescence "off state"). However, complexation with Ca 2+ induced a large enhancement effect on the fluorescence intensity of 14 and 15 from the naphthalene ring (fluorescence "on" state). Thi...

The photochemical behaviors of a series of 9-phenanthreneacetamide (PA) derivatives were investigated using UV, fluorescence, and 1 H-NMR spectroscopy in acetonitrile solutions. To apply the electron transfer (ET) action of PA as a detecting moiety of chemosensors, 4¢-(9-phenanthreneacetamido)-benzo-15-crown-5 (1) and 3¢-methyl-4¢-(9-phenanthreneacetamido)-benzo-15-crown-5 (2) were synthesized. After metal ion complex formation, the fluorescence intensity increased with increased concentration of the guest alkaline earth metal ions. The photochemical responses of the fluorescence intensity, as defined by the fluorescence intensity ratio (Imax/I0) between free and complex of 1 for Ca 2+ , was determined to be 4.76. However, the addition of guest ions in a solution of 2 greatly enhanced the fluorescence intensity of 2. The Imax/I0 of 2 was 16.6 for Ca 2+. The efficiency of ET of PA can be tuned by adding an electron-donating group onto a suitable position; fluorescent 2 was able to read out metal ions as an "Off-On" fluorescence signal.

The importance of electron-transfer reactions has attracted many researchers to investigate the fundamental steps of the processes. Especially, many studies have been devoted to photo-induced electron transfer (PET) in electron donoracceptors linked by a covalent bond system. 1 In that context, we have reported photochemical behavior of a series of donoracceptor systems. Recently, we reported that some aromatic amide derivatives that have fluorescent active groups in the molecules showed quite weak emission. The presence of Nphenyl-amide groups caused the formation of charge separation at the excited state through electron transfer between fluorescence-active groups and a benzene ring via the amide bond. Using results of a previous study, new fluorescent ionophores based on an ethyleneoxy chain containing N-phenyl-9-anthracenecarboxamide 2 and N-phenyl-1-pyrenylcarboxamide 3 were synthesized and characterized. These fluoroionophores showed weak emission corresponding to their monomers in the absence of metal ions, although their alkaline earth metal ion complexes indicated strong emissions. Their photochemical action of complexation suggested that the most likely relaxation pathway was twisted intramolecular charge transfer (TICT). To extend these investigations, we synthesized novel chemosensors based on benzo-crown ether 4 and linear polyether 5 possessing N-phenyl-1-naphthalenelacetamide. These sensors indicated that the binding of alkaline earth metal ions is signaled by a switching "on" of the naphthalene fluorescence. Fluorescence spectroscopic data suggest that their quenching process was intermolecular charge transfer involving a TICT character. These results might be construed to mean that TICT has occurred not only through the amide bond but also over the CH2 group. The concept of TICT usually emphasizes the torsion of a single bond, although the CT action of these cases was obtained over the two bonds (amide and CH2 group). The charge-transfer behavior of N-phenyl-1-naphthaleneacetamide was unique.We used 9-fluorenecarboxamide as a comparison to confirm that this CT action is peculiar to naphthalene. Fluorene has a similar UV absorption band to that of naphthalene, in addition to a unique bridge carbon out of the conjugation constructed by the biphenyl moiety. A similar UV absorption spectrum would probably use the same excited-state. The nine-positioned carbon should provide evidence for considering of the effects of the donor-acceptor distance. Fluorene is also a promising material for organic light-emitting devices because of its good chemical stability and high photoluminescence quantum efficiency, both in solution and in the solid state. 6 In addition, in the biochemical field, it has been used as "molecular beacons" for detecting nucleic acid hybridization. 7,8 Despite their advantages, applications for analytical use and signaling purposes using fluorene are rather limited.In this communication, using fluorescence, UV, and NMR spectrometries, we describe the photochemical behaviors A new fluore...