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A new redox conducting polymer, viz. poly[meso-N,N′-bis(salicylidene)-2,3-butanediaminonickel(II)], poly[meso-Ni(II)-SaldMe], belonging to the Schiff base polymer family, was electrochemically synthesized. The charge transfer and polymerization mechanism were unraveled by simultaneous cyclic voltammetry (CV) and in situ UV–vis, FTIR-ATR, and ex situ low-temperature ESR spectroscopy. With the latter, a short-living paramagnetic transient form of electro-oxidized poly[meso-Ni(II)-SaldMe] was detected. This form was identified as the bisphenolic radical cation. In situ UV–vis and FTIR-ATR spectroelectrochemistry measurements revealed that the charge transfer of the polymer involved bisphenolic radical cation formation at the potential lower than 0.80 V vs Ag/Ag+ and then dication formation at the potential exceeding 0.80 V. The proposed mechanism of electropolymerization of meso-N,N′-bis(salicylidene)-2,3-butanediaminonickel(II), meso-Ni(II)-SaldMe, involves two steps. First, electro-oxidation of the monomer...

Summary Simple synthetic procedure (reactions between iridium trichloride hydrate with a series of fluorine substituted 2-phenyl-N-methyl-benzimidazole derivatives L) leads to the cyclometallated Ir(III) complexes IrL2(acac) and IrL2(pic) where acac = acetylacetonate and pic = α-picolinate anions, respectively. All the investigated complexes exhibit strong absorption in the UV region, due to the spin allowed intra-ligand (IL) transitions, and moderately intense bands in the visible region, due to the metal-to-ligand-charge-transfer (MLCT) transitions. The complexes exhibit also strong luminescence in the deoxygenated 1:1 acetonitrile/dioxane solutions at 298 K as well as in the butyronitrile glasses at 77 K. In both experimental conditions the structured emissions (with the 0–0 transition within the 480–510 nm range of UV-Vis radiation) have been observed. Cyclic voltammetry investigations point out to reversible character of the electrochemical reactions leading to stable IrL2(acac)+ or IrL2(pic)+ cations and IrL2(pic)− anions. The corresponding IrL2(acac)− species have been found to be unstable under the applied experimental conditions (1:1 acetonitrile/dioxane solutions containing 0.1 M (C4H9)4NPF6 as the supporting electrolyte) most probably due to the irreversible electrochemical reduction of the acac− ligand. Appropriate combination of the electrochemical and luminescence properties found for the investigated complexes allows for the electron transfer generation of the excited 3∗IrL2(pic) and 3∗IrL2(acac) species. Triple-potential-step technique was used to create electrochemiluminescence (ECL) emission by annihilation of the electrochemically generated IrL2(acac)+ or IrL2(pic)+ cations and 4,4’-dicyano-biphenyl radical anion. Very high ECL emission efficiencies (close to the excited 3∗IrL2(acac) and 3∗IrL2(pic) luminescence yields) have been found.

Electrogenerated chemiluminescence (ECL) studies have been performed for the iridium(III) cyclometalated L2Ir(acac) complexes in 0.1 M (n-C4H9)4NPF6 acetonitrile–dioxane (1:1, v,v) solutions using a triple-potential-step technique. Electron transfer between electrochemically generated L2Ir(acac)+ cations and A− (radical anions of aromatic nitriles) leads to generation of the excited 3*L2Ir(acac) species. Extremely high ECL efficiencies (up to 0.55) close to the excited 3*L2Ir(acac) luminescence yields have been found.

Six new compounds, derivatives of [2,2′-bipyridyl]-3,3′-diol (BP(OH) 2 ) are recommended as useful modifications of the parent structure. One group, three molecules with conjugate aromatic substituents (6-methyl-6′-styryl-BP(OH) 2 , 6-(4-methoxystyryl)-6′-methyl-BP(OH) 2 , 6-methyl-6′-(4-phenylstyryl)-BP(OH) 2 ), are potential solar energy concentrators — they have absorption spectra red shifted with respect to BP(OH) 2 . To the second group belong the derivatives with the aliphatic side chains, better “accepted” by polyethylene than the parent molecule. These compounds are designed to improve their function as photostabilizers of polymers. All six new compounds were synthesized and their photophysical characteristics were studied. Absorption spectra, phototautomeric fluorescences and their excitation spectra, as well as quantum yields and lifetimes are reported.

The nature of the lowest triplet state of the donor–acceptor N-phenylphenothiazine derivatives has been studied by means of phosphorescence and EPR spectroscopy in various low temperature glasses. The triplet excitation of N-phenylphenothiazine and N-(p-anisyl)-phenothiazine is localised within the phenothiazine subunit. On the contrary, the 77 K phosphorescence of the molecules containing an electron acceptor group (i.e. –CN, –COCH3 or –COC6H5 at the 4′ position) is similar to that for benzonitrile, acetophenone or benzophenone, respectively, although the energy levels of their T1 states are higher than that of phenothiazine. With increasing temperature, however, their phosphorescence becomes similar to that characteristic for phenothiazine. This finding has been explained in terms of the excited-state intramolecular energy transfer accompanied by the planarisation of the phenothiazine kernel. The results of crystallographic investigations support this hypothesis.

For a few carbazole-related compounds in alcoholic solution, photoinduced solute−solvent proton-transfer dynamics are studied by means of femto- and picosecond fluorescence transient measurements. ...

Influence of intermolecular hydrogen bonding upon the vibrational pattern in the low-frequency region was studied for 2-(2-hydroxyphenyl)-3-pyridynol—a molecule which reveals both intra and intermolecular hydrogen bonds in the crystal phase. Combined use of IR and Raman spectroscopy and ab initio 6-31G∗∗ calculations for the isolated and water-complexed compound made it possible to find low frequency transitions corresponding to the vibrations of the water solvate.

We report on (sub)picosecond fluorescence studies of the mono- to diketo tautomer reaction in photo-excited [2,2′-bipyridyl]-3,3′-diol in aprotic and protic solvents. In aprotic solvents no influence of the nature of the solvent, temperature and deuteration of the hydroxyl groups on the proton transfer dynamics was found. In protic solvents, however, the proton transfer time is found to change proportionally with the viscosity coefficient of the solvent. We briefly discuss (i) the formation of the mono- and diketo forms from the dienol form and (ii) the nature of the vibrational modes assisting in the proton transfer process.

Four phototautomerizing derivatives of bipyridyl with intramolecular single and double hydrogen bonds are studied by IR and electronic spectroscopy. A broad IR band corresponding to the stretching vibration of the OH group engaged in the N⋯HO hydrogen bond is observed in all compounds in solutions, KBr tablets and low-temperature Ar matrices. Variations of excited state behaviour observed among the four molecules are well correlated with the ground state hydrogen bonding characteristics.

Excited-state intramolecular proton transfer (ESIPT) reaction has been studied in a molecule showing dual fluorescence, the 2,5-bis(2-benzoxazolyl)-4-methoxyphenol (BBMP), and its isotopomers, where the methoxy, and alternatively, the OH group has been deuterated. Attention is focused on the influence of electron donating OCH(3) substituent on fast excited state reaction. Comparison between the resonance-enhanced multiphoton ionization spectrum and the laser-induced excitation of the primary and phototautomeric emissions has been done. The geometry, electron density distribution, vibrational structure as well as the potential energy profiles in the S(0) and S(1) states of four possible rotameric forms of BBMP were calculated with application of the density functional theory (DFT). It allowed identifying the most probable conformer and assessing the role of low-frequency motions for the ESIPT efficiency.

Stationary and time-resolved studies of 9,10,19,20-tetramethylporphycene and 9,10,19,20-tetra-n-propylporphycene in condensed phases reveal the coexistence of trans and cis tautomeric forms. Two cis configurations, cis-1 and cis-2, play a crucial role in understanding the excited-state deactivation and tautomer conversion dynamics. The trans-trans tautomerization, involving intramolecular transfer of two hydrogen atoms, is extremely rapid (k ≥ 10(13) s(-1)), both in the ground and lowest electronically excited states. The cis-1-trans conversion rate, even though the process is thermodynamically more favorable, is much slower and solvent-dependent. This is explained by the coupling of alkyl group rotation with the hydrogen motion. Excited-state deactivation is controlled by solvent viscosity: the S(1) depopulation rate decreases by more than 2 orders of magnitude when the chromophore is transferred from a low-viscosity solution to a polymer film. Such behavior confirms a model for excited state deactivation in porphycene, which postulates that a conical intersection exists along the single hydrogen transfer path leading from the trans to a high energy cis-2 tautomeric form. For this process, the tautomerization coordinate includes not only hydrogen translocation but also large-amplitude twisting of the two protonated pyrrole moieties attached to the opposite sides of the ethylene bridge.

Integral electro-optical emission measurements (IEOEM) and INDO/S calculations were carried out for 2,2′-bipyridyl- 3,3′-diol (BP(OH)2), and its 5-methyl- (MeBP(OH)2) and 5,5′-dimethyl- (Me2BP(OH)2) derivatives. All three molecules were reported earlier as effective lasing dyes [5,6] undergoing photoautomerization in the S1 state. From the IEOEM experiment an upper limit of about 1.0 D (debye) is derived for the fluorescent state dipole moment, μe, in each case, while the INDO/S calculations predict μe of the excited singlet (π, π∗) state of the diketo and monoketo forms in the range: 0.0–0.5 D and 4.0–4.9 D, respectively. Comparison of both results leads to an unequivocal discrimination between the two possible photoreactions, single or double proton transfer (SPT or DPT), and shows that the fluorescent species are diketo tautomers produced by DPT.

2,2′-bipyridyl-3,3′-diol and its dimethyl derivative undergo an ultrafast double-proton transfer upon excitation to S 1 state, and no direct population of T 1 state is observed. Thus, the primary (dienol) triplet (T 1 ) was populated, both by sensitization from the toluene triplet and by enhancement of the forbidden T 1 ←S 0 absorption. The low-energy phosphorescence of the phototautomeric (diketo) triplet was detected by irradiation in bromobenzene and was quenched by O 2 ( 3 Σ − g ) to yield O 2 ( 1 Δ g ). The triplet state is located at 21300 ± 300 and 12700 ± 100 cm −1 for the primary and phototautomeric form, respectively, in good agreement with the values predicted by the INDO/S method.

The scope of the present work is the investigation of proton transport through monomolecular Langmuir-Blodgett (LB) films. The films were formed from amphiphilic molecules: 2-naphtholo-6-sulfonamide of dodecylamine (N) and 1,4-anthraquinono-2 sulfonamide of dodecylamine (A). The 2-naphthol derivative can act as a proton donor due to excited state proton transfer (ESPT) and the 1,4-anthraquinone group can play the role of proton acceptor because of protonation of the reduced form if it is present. Absorption and emission spectra of LB films containing N and A were registered and separated into component bands. Individual absorption and emission peaks observed were assigned to given forms of chromophores. The behavior of different component bands reflects the state of anthraquinone dependent on proton concentration. A correlation of rate and efficiency of ESPT, with changes of the spectra of A, may be expected to yield information concerning the transport of protons from N to A. The influence of the donor-acceptor distance, sample humidity, film arrangement and the presence of protonophores (Gramicidin A) on proton transfer is studied. Our results indicate that the proton can be transported through the film but its concentration vanishes at the distance greater than 30 A. The efficiency of proton transfer depends strongly on water content, film structure and the presence of ion channels.

All observed IR-active vibrational modes of [2,2′-bipyridyl]-3,3′-diol (BP(OH)2) and its two isotopomers, BP(OD)2 and BP(OH)2-d6 have been assigned on the basis of the comparison of experimental results with predictions obtained from DFT (B3LYP/6-31G(d,p)) calculations. The sensitivity of the vibrational transitions to the environment has been studied by comparing the spectra recorded in vapour, different solutions, KBr pellets, and cryogenic argon matrices. The results may be useful for the quantum control of excited state single or double proton transfer in BP(OH)2.

A femtosecond study of the intramolecular proton transfer dynamics in photoexcited mono- and dienol derivative compounds of pyridine is reported. It is shown that when a strongly electron-withdrawing substituent is attached to [2,2′-bipyridyl]-3,3′-diol, the excited-state proton transfer of this compound is changed from a double-proton transfer to a single-proton transfer. The excited-state single-proton transfer time in the title compounds is

Microassociation of poly(N-vinylcarbazole) by a focused near-infrared laser beam (cw-YAG, 1064 nm) was first demonstrated in organic solvents. Investigations were made in cyclohexanone and N,N-dime...

Two new bipyridyl derivatives undergoing the excited state intramolecular proton transfer were synthesized: 5-methyl-[2,2′-bipyridine]-3,3′-diol and 5,5′-dimethyl-[2,2′-bipyridine]-3,3′-diol. Both reveal a strong phototautomeric, largely Stokes-shifted fluorescence and can be used as proton transfer laser dyes. Tuning ranges and lasing efficiences are also reported.