External Heavy Atom Effect Research Articles

Studies on unimolecular and bimolecular photoprocesses of a newly synthesized selenium compound, 7-chloro-2-phenyl-9 H-[1]-benzopyrano[3,2- b]-selenophene-9-one (SeP)

Using steady state/time resolved spectroscopic and electrochemical techniques the spectroscopic and photophysical studies were made on a novel synthesized selenophene compound SeP in nonpolar methylcyclohexane (MCH), polar aprotic acetonitrile (ACN) and polar protic ethanol (EtOH) solvents at the ambient temperature as well as at 77 K. Both from the studies on unimolecular and bimolecular photoprocesses this selenophene compound was found to possess several electronic levels, 1B b, 1L a, 1L b (all are of ππ* nature and 1L b is hidden within 1L a band envelop like the characteristics of most of the acenes) and 1(n Oπ*) state arising due to carbonyl oxygen atom. In polar ACN environment this n Oπ* state disappears because it moves within the envelop of intense 1L a band due to large destabilization. Large overlapping of different band systems within the 1L a band of SeP was confirmed from the observed depolarization effect. The lack of phosphorescence of SeP both in MCH and EtOH rigid glassy matrix at 77 K has been inferred due to large vibronic interactions between closely lying triplets of the corresponding 1n Oπ* and 1L b states. From the bimolecular investigations, it reveals that SeP acts as a good electron donor in presence of the well known electron acceptor 9 cyanoanthracene (9CNA). Transient absorption spectra measured by laser flash photolysis technique demonstrate the formation of ion-pair when the acceptor is excited. From the analysis of the fluorescence quenching data it seemingly indicates that the major contribution in the diminution of the fluorescence intensity of the acceptor 9CNA in presence of SeP is not only due to the photoinduced electron transfer (ET) but also originates from static type (instantaneous) quenching processes along with external heavy atom effect. The possibility of occurrence of photoinduced ET reaction in Marcus inverted region is hinted.

Effect of halogenated compounds on the photophysics of C 70 and a monoadduct of C 70: Some implications on optical limiting behaviour

The fluorescence spectra, quantum yields and lifetimes of C 70 and a pseudo-dihydro derivative (C 70R) have been measured in a wide range of solvents at room temperature. This information is important for the development of reverse saturable absorbers. Phosphorescence spectra and phosphorescence lifetimes were also measured at low temperature. The fluorescence is subject to quenching by halogenated compounds. The efficiency of quenching follows the order I>Br≫Cl. The nature of the quenching is shown to vary, with chlorinated compounds exhibiting static quenching of fullerene fluorescence, owing to nonfluorescent complex formation, whilst those compounds containing bromine and iodine exhibit dynamic quenching due to the external heavy-atom effect, that increases the intersystem crossing rate constant in the fluorophore–perturber complex. This constant is evaluated by an original method from the bimolecular quenching rate constants. The phosphorescence quantum yield of both fullerenes at 77 K slightly increases in the presence of iodobenzene, in spite of a strong decrease in phosphorescence lifetime. The marked increase of the intersystem crossing rate constant in concentrated solutions owing to the external heavy-atom effect is of interest for the application of fullerenes as fast-responding optical limiters (reverse saturable absorbers) of intense laser pulses, even in cases where the triplet quantum yield is of the order of unity.

High-Resolution Ultraviolet Spectroscopy of Neutral and Ionic Clusters: Hydrogen Bonding and the External Heavy Atom Effect

High-Resolution Ultraviolet Spectroscopy of Neutral and Ionic Clusters: Hydrogen Bonding and the External Heavy Atom Effect

Influence of interaction of chromophores, linked by the unconjugated chain, on the luminescence properties of biscyanine dyes

Deactivation of electronically excited state of chemically bound dimers – biscyanines with two chromophores linked by unconjugated chains and corresponding monomer dye was investigated. It was found that the quantum yield of dimer fluorescence is lower than that of a monomer dye. The amount of quantum yield of fluorescence decreases with the increase of chromophores interaction degree (the decrease of the isolating polymethylene bridge length). It is shown on the basis of the external heavy-atom effect studies that the decrease of biscyanines fluorescence ability is connected with the enhancment of singlet–triplet intersystem crossing ( S 1⤳ T 1 ). It has been established that the probability of the triplet states population in biscyanines with chromophores in parallel arrangement is considerably higher than that in similar compounds with an angular arrangement of chromophores. The delayed fluorescence was observed in the case of dyes with parallel arrangment of chromophores.

A Systematic Study of the Photophysical Processes in Polydentate Triphenylene-Functionalized Eu3+, Tb3+, Nd3+, Yb3+, and Er3+ Complexes

m-Terphenyl-based lanthanide complexes functionalized with a triphenylene antenna chromophore ((Ln)1) exhibit sensitized visible and near-infrared emission upon photoexcitation of the triphenylene antenna at 310 nm. Luminescence lifetime measurements of the (Eu)1 and (Tb)1 complexes in methanol-h1 and methanol-d1 revealed that one methanol molecule is coordinated to the lanthanide ion, indicating that all eight donor atoms provided by the ligand are involved in the encapsulation of the lanthanide ion. The luminescence lifetimes of the near-IR-emitting complexes (Er)1, (Nd)1, and (Yb)1 in DMSO-h6 and DMSO-d6 are in the microsecond range, and are dominated by nonradiative deactivation of the luminescent state. The processes preceding the lanthanide luminescence in the sensitization process have been studied in detail. The complexed lanthanide ion reduces the antenna fluorescence and increases the intersystem crossing rate via an external heavy atom effect. The subsequent energy-transfer process was found to take place via the antenna triplet state in all complexes. Luminescence quantum yield measurements and transient absorption spectroscopy indicated that in solution two conformational isomers of the complexes exist: one in which no energy transfer takes place, and one in which the energy transfer does take place, resulting in the lanthanide luminescence. The intramolecular energy-transfer rate is higher in the (Eu)1 and (Tb)1 complexes than in the near-infrared-emitting complexes. In methanol the energy-transfer rate is 3.8 × 107 s-1 for (Eu)1 and (Tb)1. In DMSO-d6 the intramolecular energy-transfer rate is higher in the (Nd)1 complex (1.3 × 107 s-1) than in the (Er)1 (3.8 × 106 s-1) and (Yb)1 (4.9 × 106 s-1) complexes.

External heavy-atom effect on fluorescence kinetics

Fluorescence quenching in fluid solution by the external heavy-atom effect usually follows simple Stern?Volmer kinetics, and the quenching effect is gauged by the magnitude of the bimolecular quenching rate constant. However, it is the increased unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore in the perturber?fluorophore complex that can be directly compared with that of the unperturbed fluorophore. From a simple model for external heavy atom quenching in fluid solution, the decay law is predicted to be singly exponential for all quencher concentrations, and a new expression for the unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore is obtained. The same problem, but in rigid solution, is also discussed for the first time. The model now predicts a nonexponential fluorescence decay law, from which the unimolecular S1→Tn intersystem crossing rate constant of the perturbed fluorophore can be directly determined.

Photophysics of 4-methoxy-benzo[b]thiophene in different environments. Its role in non-radiative transitions both as an electron and as an energy donor

The present investigation was made to study the photophysical properties of a newly synthesized benzothiophene compound “4-methoxy-benzo[b] thiophene (4MBT)” in different environments both at the room and at 77 K temperatures. The studies were mainly made by electrochemical and spectroscopic (both by steady-state and time resolved) techniques. The presence of the heteroatom sulfur (S) in 4MBT seems to be responsible for the observed significant changes in the transition energies of this molecule compared to that of analogous compound 4-methylindole (4MI) in spite of the structural similarities of these two compounds. In the presence of the electron acceptors 2-nitrofluorene (2NF) and 9-fluorenone (9FL) the room temperature fluorescence spectra of 4MBT are found to be quenched significantly. In the presence of the latter quencher, a long-wavelength band was found to develop at around 508 nm region with a concomitant reduction in the 4MBT fluorescence band. Fluorescence lifetime data reveal that this long-wavelength band might be due to the formation of acceptor fluorescence by Förster's long-range singlet–singlet energy transfer process. The observed highly negative Δ G 0 values of the present donor-acceptor systems coupled with large overlapping of fluorescence spectra of the donor and electronic absorption spectra of the acceptor are explained by competing energy transfer and photoinduced electron transfer (ET) reactions. In the presence of the acceptors, presently studied, excited donor 4MBT deactivates non-radiatively through both the static and the dynamic quenching processes in which the former process appears to be dominant. Positive deviation from linearity of Stern–Volmer (SV) plot along with the observation of unaffected fluorescence lifetime of 4MBT in the presence of different concentrations of the quenchers (acceptors) demonstrates this fact. In dynamic quenching, Förster's energy transfer process appears to play a major role. However, when acceptors are excited to their first singlet excited states in the presence of unexcited (ground state) donor 4MBT, only dynamic processes (ET associated with some other non-radiative processes) seem to be operative. From the present investigations it was inferred that benzothiophene is a stronger electron donor than the analogous compound 4MI, though the structures of these two donors are similar except for the presence of a heavy atom S in the 1-position of 4MBT. At 77 K as the value of R 0, Förster critical energy transfer distance, is high (∼20 Å), the quenching of the donor fluorescence by the acceptors seems to proceed mainly through the Förster's energy transfer mechanism. The reduction of phosphorescence intensity of this donor in the presence of an acceptor seems to be due to the involvement of a non-radiative pathway through which singlet – singlet ( S D 1→ S A 1) energy transfer occurs efficiently followed by intersystem crossing to populate the triplet level of the acceptor at the expense of the population in donor triplet. At this temperature the exact mechanism of the observed fluorescence quenching effect of the acceptor (2NF and 9FL) in the presence of the donor 4MBT containing S atom is not very clear at the present stage of investigation. Two possible non-radiative mechanisms, one by external heavy-atom effect and the other by photoinduced ET process, seem to have minor role at 77 K as sulfur is known to be weak heavy-atom perturber and ET is thermally activated process.

Internal and external heavy-atom effects on phosphorescence radiative lifetimes calculated using a mean-field spin–orbit Hamiltonian

Abstract We investigate the performance of an atomic mean-field approximation to the spin–orbit interaction Hamiltonian in calculations of phosphorescence radiative lifetimes. A comparison of the performance of the mean-field approximation with the full spin–orbit interaction operator is made for the phosphorescent radiative lifetimes of the 3 B 1u excited state of ethylene perturbed by an external halogen ion, and for the 3 A 1 and 3 B 1 excited states in mono- and di-halogen-substituted pyridines. The mean-field approximation is shown to give excellent results compared to calculations with the full one- and two-electron spin–orbit integrals.

ODMR and fluorescence studies of pyrene solubilized in anionic and cationic micelles

The luminescence of pyrene solubilized in anionic sodium n-alkyl sulfate (NaC n S, n=10, 12) and cationic trimethyl-n-alkyl-ammonium bromide (C n TABr, n=10, 12, 14, 16) micelles was studied using zero field optically detected magnetic resonance (ODMR) at cryogenic temperatures and fluorescence quenching techniques at room temperature. The values of triplet state phosphorescence wavelengths and zero-field splitting parameters D in the micelles are consistent with a pyrene microenvironment which is intermediate in polarity and polarizability between an alkyl chain-like environment and an aqueous solvent. The triplet state properties vary reproducibly with surfactant chain length, indicating slight differences in the pyrene environment in the different micelles, but there are no monotonic trends. Pyrene phosphorescence and fluorescence lifetimes in the C n TABr micelles are shortened by the external heavy atom effect of the bromide counterions; the C 10TABr micelle shows the shortest lifetimes, indicating enhanced counterion proximity to pyrene. Quenching of pyrene fluorescence by added acrylamide was measured for the C n TABr micelles by both steady state and fluorescence decay methods. The apparent dynamic quenching constant in the micelles is nearly three orders of magnitude smaller than its value in aqueous solution, and shows a small but monotonic decrease with increasing surfactant chain length.

Matrix Isolation Fourier Transform Infrared and Ab Initio Studies of the 193-nm-Induced Photodecomposition of Formamide

Ultraviolet irradiation of formamide in solid argon forms hydrogen-bonded, carbon- and oxygen-attached complexes NH3−CO and NH3−OC. Computationally, the carbon-attached complex is 1.2 kJ mol-1 more stable than the oxygen-attached complex. However, a thermal equilibrium of the two structures is found experimentally in the matrices. Moreover, the oxygen-attached complex dominates in the 193-nm-induced photolytic complex formation from formamide. In xenon matrices, the photochemistry of formamide increasingly yield the HNCO+H2 binary system. The change in photochemistry of formamide between the argon and xenon enviroments can be attributed to an external heavy-atom effect, where xenon enhances the rate of intersystem crossing from a singlet to a triplet surface.

Fluorescence and Phosphorescence Properties of Naphthalene in Aqueous d-Glucose Solutions Containing 6-Deoxy-6-iodo-β-cyclodextrin at Room Temperature

Abstract In aqueous solutions, 6-deoxy-6-iodo-β-cyclodextrin (β-CDI) forms a 1 : 1 inclusion complex with naphthalene. The naphthalene fluorescence is quenched upon the formation of the inclusion complex with β-CDI. The room-temperature phosphorescence of naphthalene has been observed from aqueous naphthalene solutions containing both d-glucose and β-CDI. Although the room-temperature phosphorescence has also been observed from aqueous naphthalene solutions containing both d-glucose (5.0 g/5.0 mL) and β-cyclodextrin (1.0 × 10−2 mol dm−3), its intensity amounts to at most 9% of that containing d-glucose (5.0 g/5.0 mL) and β-CDI (1.0 × 10−3mol dm−3). In addition to the high viscosities of d-glucose solutions, the external heavy atom effects of β-CDI cause the appearance of the room-temperature phosphorescence. The room-temperature phosphorescence quantum yield of naphthalene in d-glucose (5.0 g/5.0 mL) solution containing β-CDI (1.0 × 10−3 mol dm−3) has been estimated to be 2.2 × 10−3, which is around 1.8% of the intrinsic phosphorescence quantum yield of naphthalene in ethanol at 77 K.

External heavy atom effects of 6-deoxy-6-iodo- α-cyclodextrin on the room-temperature phosphorescence of 6-bromo-2-naphthol and 3-bromoquinoline in aqueous solutions

6-Deoxy-6-iodo- α-cyclodextrin ( α-CDI) has been found to form a 1:1 inclusion complex with 6-bromo-2-naphtho). A further association occurs between the 1:1 inclusion complex and an additional α-CDI molecule, leading to the formation of a 2:1 α-CDI-6-bromo-2-naphthol inclusion complex. The room-temperature phosphorescence of 6-bromo-2-naphthol is observed from the 2:1 α-CDI-6-bromo-2-naphthol inclusion complex, whereas the 1:1 inclusion complex does not emit it. The room-temperature phosphorescence intensity for the 2:1 α-CDI-6-bromo-2-naphthol inclusion complex is reduced by about 18% relative to that for the 2:1 inclusion complex composed of the parent α-CD, indicating the external heavy atom effects of α-CDI on the bound guest. The external heavy atom effects of α-CDI have also been examined on the room-temperature phosphorescence intensity of 3-bromoquinoline buried within the α-CDI cavity. At the same CD concentrations (2.O × 10 −3 mol dm −3), the room-temperature phosphorescence for α-CDI has been decreased by about 10% relative to that for α-CD.

Excited Singlet State Reactions of Thiopyrylium with Electron Donors: Electron Transfer, Induction of Triplet by Internal and External Heavy Atom Effect, and Comparison of Pyrylium and Thiopyrylium Reactions

The free energy dependence on the fluorescence quenching of 2,4,6-triphenylthiopyrylium tetrafluoroborate (TPTP) by a variety of halogenated benzenes, toluenes, and anisoles were studied in acetonitrile. The kq values calculated using ΔG⧧ from the Levine expression and the kd value of 5.4 × 1010 M-1 s-1 from the Smoluchowski expression are in good agreement with the experimental kq values. The observation of the TPTP• signal at 550 nm and the correlation of kq with ΔGet expound the possibility of an electron-transfer mechanism. The radical yield and intersystem-crossing rate constants are evaluated using flash photolysis techniques. The influence of sulfur atom in the triplet induction is reflected in the intersystem-crossing rate constant and radical yield values. The recombination rate constants kb obtained from the radical yield values are compared with the kb values calculated using the semiclassical expression.

Luminescence and structure of the protonated forms ofmeso-tetraarylporphyrins in solution

A comparative study of the spectral-luminescent properties (at 293 K and 77 K) of meso-tetrakis(o-tolyl)porphyrin (o-TTP) and meso-tetraphenylporphyrin (TPP), and also meso-tetrakis(n-propyl)porphyrin (TPrP) in nonaqueous acid media has been carried out with the aim to reveal effects associated with the influence of methyl groups which hinder sterically the twist of the phenyl rings enhancing their conjugation with the macrocycle in acid medium. On the basis of the spectral data it is concluded that although the introduction of the methyl groups diminishes this twist of phenyls it does not eliminate it completely (the absorption spectra of protonated o-TTP are intermediate between those of TTP and TPrP). The fluorescence spectra of the protonated forms of o-TTP and TPP at 77 K are approximately mirror-symmetrical to the Q(0-0) and Q(0-1) absorption bands; on the elevation of the temperature up to 293 K the fluorescence and absorption bands broaden, the Stokes shift largely increases, and the mirror symmetry of the spectra disappears, which is indicative of changes in solute-solvent interactions in the S1 state. The analysis of the obtained data on the energetics of photophysical processes leads to the conclusion that the significant role of radiationless deexcitation in the S1-->S0 channel, characteristic of the protonated form of TPP, is retained at 77 K. The introduction of the methyl groups at the ortho positions sharply decreases the corresponding rate constant, so that the S1-->T1 intersystem crossing becomes the main channel of deexcitation. The influence of heavy atoms (the Cl- and Br- anions) on the luminescence of the protonated forms has been investigated. It is shown that, analogous to the case of octaethylporphyrin investigated earlier, in nonaqueous media the protonated species of o-TTP form bis adducts of the dihydrochloride type. Contrary to this, the experiments with meso-tetrakis(p-sulfophenyl)porphyrin (TPPS) in aqueous solutions have shown that the TPPS dications do not add counterions, whereas the influence of Cl- and Br- on fluorescence is realized according to the external heavy-atom effect mechanism. For nonaqueous o-TTP solutions with admixtures of HCl and CF3COOH the short-wavelength fluorescence from the S3 (B1) level has been detected whose unusual peculiarity is its enhancement in passing from 293 K to 77 K.

Luminescence and structure of the protonated forms of meso‐tetraarylporphyrins in solution

A comparative study of the spectral-luminescent properties (at 293 K and 77 K) of meso-tetrakis(o-tolyl)porphyrin (o-TTP) and meso-tetraphenylporphyrin (TPP), and also meso-tetrakis(n-propyl)porphyrin (TPrP) in nonaqueous acid media has been carried out with the aim to reveal effects associated with the influence of methyl groups which hinder sterically the twist of the phenyl rings enhancing their conjugation with the macrocycle in acid medium. On the basis of the spectral data it is concluded that although the introduction of the methyl groups diminishes this twist of phenyls it does not eliminate it completely (the absorption spectra of protonated o-TTP are intermediate between those of TTP and TPrP). The fluorescence spectra of the protonated forms of o-TTP and TPP at 77 K are approximately mirror-symmetrical to the Q(0–0) and Q(0–1) absorption bands; on the elevation of the temperature up to 293 K the fluorescence and absorption bands broaden, the Stokes shift largely increases, and the mirror symmetry of the spectra disappears, which is indicative of changes in solute-solvent interactions in the S1 state. The analysis of the obtained data on the energetics of photophysical processes leads to the conclusion that the significant role of radiationless deexcitation in the S1 ↝ S0 channel, characteristic of the protonated form of TPP, is retained at 77 K. The introduction of the methyl groups at the ortho positions sharply decreases the corresponding rate constant, so that the S1 ↝ T1 intersystem crossing becomes the main channel of deexcitation. The influence of heavy atoms (the Cl− and Br− anions) on the luminescence of the protonated forms has been investigated. It is shown that, analogous to the case of octaethylporphyrin investigated earlier, in nonaqueous media the protonated species of o-TTP form bis adducts of the dihydrochloride type. Contrary to this, the experiments with meso-tetrakis(p-sulfophenyl)porphyrin (TPPS) in aqueous solutions have shown that the TPPS dications do not add counterions, whereas the influence of Cl− and Br− on fluorescence is realized according to the external heavy-atom effect mechanism. For nonaqueous o-TTP solutions with admixtures of HCl and CF3COOH the short-wavelength fluorescence from the S3 (B1) level has been detected whose unusual peculiarity is its enhancement in passing from 293 K to 77 K. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 121–133, 1998

Phosphorescence study of 1-bromonaphthalene in aerated aqueous solution of surfactant and β-cyclodextrin

Surfactant (S) induced room-temperature phosphorescence (RTP) from 1-bromonaphthalene (1-BrN) in aerated aqueous solution of β-cyclodextrin ( β-CD) has been investigated in detail. Benesi-Hildebrand analyses indicate that bright phosphorescence arises from a stable 1/S-BrN: β-CD ternary complex in aqueous solution. Of the surfactants employed, cetylpyridinium bromide (CPB) shows much lower phosphorescence enhancement than cetyltrimethylammonium bromide (CTAB) and polyethylene tert-octyl phenyl ether (OP), and sodium dodecylbenzene sulfonate (SDBS) shows higher phosphorescence enhancement than Tween-20 and sodium dodecyl sulfate (SDS), respectively since the intermolecular energy transfer occurs between 1-BrN in the cavity and an aromatic group of a surfactant in a ternary complex. Simultaneously, the external heavy-atom effect of 1-BrN results in the fluorescence quenching of OP and SDBS, In combination with equilibrium constants, surface tension of solutions and spectral structure, a comparison of molecular size shows that part of the hydrocarbon chain of surfactants is included in the cavity of β-CD and the hydrophobic part with the polar head group located outside the cavity coils at the mouth of β-CD cavity. As a result, the excited I-BrN is shielded from the efficient phosphorescence quenching oxygen molecules dissolving in water and intense RTP is obtained.

New and Unusual Bonding in Open Shell van der Waals Molecules Revealed by the Heavy Atom Effect: The Case of BAr

Calculations are reported for the excited 14Π and C2Δ electronic states of BAr and the (nominally 2s2p2) 4P and 2D states of atomic boron. It was found necessary to extend an augmented valence triple-zeta orbital basis set to correctly describe the C2Δ state. This enhancement is necessitated by the near degeneracy of the valence 2s2p2 2D and Rydberg 2s23d 2D electron configurations in atomic boron, both of which are required to describe BAr C2Δ. Unexpectedly strong bonding in the C2Δ state is found. This bonding is shown to have its root in a type of coordinate covalency, dative bonding, that is sensitive to electron correlation effects and is reflected in a large external heavy atom effect in the spin−orbit coupling of the 14Π and C2Δ states.

Picosecond dynamics of the S 2 excited state of azulene and its van der Waals complexes with Ar and Xe

The dynamics of the second excited singlet (S 2) states of jet-cooled azulene (Az) and its van der Waals complexes with one and two atoms of Ar and Xe have been investigated. Quantum interference effects due to restricted intramolecular vibrational redistribution in azulene have been reinterpreted. Lifetime shortening in the 1:1 and 1:2 complexes with Xe is attributed to an enhancement of the rate of S 2T 1 intersystem crossing by the external heavy atom effect. Excitation of the complexes to states with E vib > E b produces energy-resolved fluorescence decays which exhibit sequential intramolecular vibrational redistribution-vibrational predissociation.

The Role of Time‐Dependent Measurements in Elucidating Static Versus Dynamic Quenching Processes

Abstract— Fluorescence quenching provides a unique method for assessing the ability of quenching species to approach a fluorophore. The distance scale depends on the mechanism of quenching (e.g. compare Forster energy transfer with the external heavy atom effect and/or electron transfer). If one is dealing with amphiphilic systems or hydrophobic surface/water interfaces then ionic and organic quenchers can be compared. While the general concepts of “static” and “dynamic” quenching are well known and often used to characterize the mechanism of fluorescence quenching, it is this author's experience that for many systems the quenching mechanism is “mixed.” The signature of this situation is when the quenching of the steady‐state intensity does not match the quenching of the average fluorescence lifetime. First a few of the standard quenching models are reviewed and then a simple approach to characterize the degree of static quenching is discussed. Finally, it is indicated that careful analysis of the fluorescence decay for the shortest timescale should be undertaken if one wishes to estimate accurately the rate of static quenching and that this may be expected to be particularly demanding in the case of fluorophores with longer lifetimes. Although fluorescence is stressed in the discussion that follows, the same concepts would apply to phosphorescence from triplet states, except for the generally longer timescale encountered.

Cation-sensitive fluorescence of anionic polymers bearing naphtho-18-crown-6 units

Changes in the fluorescence intensity of anionic polymers bearing naphtho-18-crown-6 moieties on addition of cations were studied in water at 30 °C. On addition of alkali metal cations, the fluorescence intensity of the polymers decreased sharply for Tl(+) less for Cs(+) and little for Li(+), K(+) and Rb(+). On addition of alkaline earth metal cations, Ba(2+) caused the strongest decrease of the fluorescence intensity of the polymers. The decrease of the fluorescence intensity of the polymers was suggested to be caused by the external heavy-atom effect of the cations bound to the cavity of the crowned naphthalene moiety. The content of the crowned naphthalene units in the polymers affected the cation-dependent fluorescence change. The fluorescence change of the polymers based on the cation complexation competition was also studied.