Chemistry

The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton of drugs in therapeutic applications, has recently been the subject of increasing interest due to the finding of their phototoxic and photocarcinogenic properties. Its absorption and fluorescence behavior from different prototropic species show remarkable sensitivity towards the polarity, viscosity and local pH, exhibited by various microheterogeneous bio and

The work describes the synthesis and characterization of salicylaldazine by CHN analysis, IR, NMR and single crystal X-ray diffraction. The compound C 14 H 12 N 2 O 2 crystallizes in the monoclinic crystal system with the space group P2 1 /n, a = 8.554(3) Å, b = 6.338(2) Å, c = 11.864(5) Å, and β =107.89(2) 0. There are two strong intramolecular hydrogen bonds of the type O-HLN and two intermolecular hydrogen bonds of the type C-HLN which help the molecules to pack in a layered structure. Semiempirical calculations have also been performed to predict theoretically the feasibility of intramolecular ground and/or excited state proton transfer reaction/s. Potential energy curves have been generated in the ground (S 0) and the lowest excited (S 1) states to judge the feasibility of intramolecular single and double proton transfer reactions. Semiempirical (AM1) calculations suggest that only the excited state intramolecular single 2 proton transfer process is favored both thermodynamically and kinetically. No other prototropic processes are theoretically feasible.

In the present article, we have investigated the photophysical behavior of 3-hydroxyflavone (3HF), an excited state intramolecular proton transfer (ESIPT) probe, in aqueous solutions of two imidazolium-based room temperature ionic liquids (RTILs), one micelle-forming and the other non micelle-forming, exploiting steady state and time resolved fluorometric techniques. The study unveils that the ESIPT process of 3HF is modified substantially in the micelle-forming RTIL as compared to that in the other RTIL. The critical micellar concentration (CMC) of the micelle-forming RTIL has been determined from both steady state and time resolved data. The study suggests that 3HF resides within the micellar phase and experiences significantly less polar environment in its vicinity than in the non micelle-forming ionic liquid. A comparative study with the probe in the micelle-forming ionic liquid and a conventional anionic surfactant of a similar hydrophobic chain length reveals that 3HF experien...

The excitation of 3-hydroxyflavone (3HF) to its second excited singlet state (S 2) gives rise to dual fluorescence in supercritical carbon dioxide. The ultraviolet fluorescence originated from the S 2 state of 3HF is well separated from the green emission emanating from the tautomeric form, produced via the excited state intramolecular proton transfer. The relative intensity of the S 2 to the tautomer fluorescence (S 2 /T) has been studied as a function of pressure and temperature. It is shown that this ratio reflects the microheterogeneity of the supercritical CO 2 , and confirms the value of fluorometric probes in disclosing the microscopic properties of supercritical fluids.

Laser induced optoacoustic spectroscopy has been used to determine the relative contribution of the intersystem crossing and internal conversion to the non-radiative energy dissipation from the two excited ICT probes p-N,N-dimethylaminobenzonitrile (DMABN) and p-N,N-dimethylaminobenzaldehyde (DMABA) in solvents of different polarity. It is observed that while intersystem crossing is the main non-radiative deactivation process for DMABN in all the solvents studied this is not the case in polar solvents for DMABA.

Steady state photophysics of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) has been studied in different pure and mixed solvents. The fluorometric behaviour of AODIQ is modified dramatically with a change in the solvent polarity. The fluorescence quantum yield, when plotted against the solvent polarity parameter (E T ð30Þ), passes through a maximum. Plot of the fluorescence parameters in a graded series of dioxane-water mixture against E T ð30Þ shows segmented linearity with two independent slopes; reflecting a lower sensitivity in the less polar region and a much higher sensitivity in higher polarity range. The observations lead to the proposition that the fluorescence of AODIQ originates from two different states, viz., a locally excited (LE) and a charge transfer (CT) one. Studies of the phosphorescence and heavy atom quenching of the fluorescence reveal that the CT state lies above the lowest triplet state even in a very polar environment.

The excitation of 3-hydroxyflavone (3HF) to its second excited singlet state (S 2) gives rise to dual fluorescence in supercritical carbon dioxide. The ultraviolet fluorescence originated from the S 2 state of 3HF is well separated from the green emission emanating from the tautomeric form, produced via the excited state intramolecular proton transfer. The relative intensity of the S 2 to the tautomer fluorescence (S 2 /T) has been studied as a function of pressure and temperature. It is shown that this ratio reflects the microheterogeneity of the supercritical CO 2 , and confirms the value of fluorometric probes in disclosing the microscopic properties of supercritical fluids.

The fluorescence properties of 4-methyl-2,6-diamidophenol MDOH are examined in some non-polar solvents in relation Ž. to 4-methyl-2,6-diformyl phenol MFOH and quantum yield measurements are made at room temperature and 77 K. The Ž. Ž y1. excited state intramolecular proton transfer ESIPT is evidenced by a large Stokes-shifted emission ; 9000 cm which is likely to originate from the enol tautomer. From nanosecond measurements and quantum yields of fluorescence, we have determined proton transfer rates. It is observed that the non-radiative channels are always dominant in the decay processes of the excited state of MDOH. At 77 K, MDOH exhibits, like MFOH, phosphorescence in all the non-polar solvents studied here and the conversion of fluorescence into phosphorescence in the case of MDOH is relatively slow compared to that of MFOH.

Photophysical properties of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) have been studied in different aqueous micellar environments using steady-state and time-resolved emission spectroscopy. The charge transfer (CT) fluorescence exhibits appreciable hypsochromic shift, along with an enhancement in the fluorescence intensity in all the micellar media. This is associated with an increase in the fluorescence anisotropy (r), which suggests that the fluorophore molecule experiences motionally restricted environments upon binding with the micelles. Fluorescence spectral position and fluorescence quenching studies suggest that the fluorescing moiety does not penetrate into the core of the micellar units; rather it binds at the micelle-water interfacial region. The binding constant and free energy change during probe-micelle binding have been evaluated from relevant fluorescence data. Light has been thrown on the mode of action of urea on micelle bound probes. The results are interpreted in terms of the model that urea displaces water molecules from the micellar interface and the consequent destabilization leads to the expulsion of the probe molecules from the interfacial region. Polarity and viscosity of the microenvironments around the probe have been determined in the micellar systems.

Absorption spectra and fluorescence data in nonpolar solvents are reported for seven novel dehydroabietic acid-based diarylamines, which have potential as components of hole transport layers for molecular electronic devices. This bulky group has been found to improve the possibilities for film formation of these compounds, and in this study we show that this does not significantly affect their fluorescence characteristics, which are similar to diphenylamine.

Absorption as well as steady-state and time-resolved emission studies of p-dimethylaminobenzaldehyde (DMABA) in aqueous B-cyclodextrin (/3CD) solutions have been reported. Dual fluorescence corresponding to the non-polar (NP) and twisted intramolecular charge transfer (TICT) has been observed. Two types of ground state DMABA-flCD complexes are proposed. Fhe twisted intramolecular charge transfer (TICT) emission is severely suppressed for the complex where the fluorophore is totally encapsulated but it is enhanced due to the reduced polarity imposed by the /3CD-microenvironment for the complex where DMABA is only partially enclosed.

Steady state and time-resolved fluorometric investigations of the excited state proton transfer reactions of carbazole and 2-naphthylamine in the presence of P-cyclodextrin are reported in this paper. The results, together with earlier reports, reveal that the prototropic reaction depends not only on the microenvironment of the molecule, which is imposed by cyclodextrin, but also on the nature of the molecule itself. Thus, in comparison with the bare chromophore, the deprotonation.rate of the cyclodextrin inclusion complex is enhanced when the guest molecule is carbazole, whereas it is decreased for guests like naphthylamine or naphthols.

The photoprocesses like excited state proton transfer (ESPT), intramolecular charge transfer (ICT), fluorescence energy transfer (FET), occurring in the excited molecules find ample applications in the chemical and biochemical fields. These photoprocesses are markedly affected by the introduction of biomimicking liquid confining environments like micelles, reverse micelles, cyclodextrins, proteins, etc. The local polarity, viscosity and pH, induced by the confined environments have a significant role in modifying the photoprocesses. In this review we have presented a comprehensive report of the recent progress in the study of these photoprocesses in photoexcited molecules in different confined liquid environments. Mostly, recent works have been reviewed in this article to acquire information about progress in the photophysical and photochemical reactions in different confined environments.

Steady state absorption and fluorometric techniques have been used to investigate the photophysics of norharmane (NHM), a bioactive fluorophore, in aqueous as well as aqueous cyclodextrin (CD) environments. The absorption and steady state fluorescence spectral studies reveal the formation of two types of inclusion complexes between the fluorophore and b-cyclodextrin (b-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined monitoring the fluorescence data. a-and c-cyclodextrin (a-CD, c-CD) do not have appreciable effect on the spectral pattern of the fluorophore. The differential fluorimetric behavior of NHM in different CD environments has been rationalized from the variation of the relative dimensions of the probe and the CD cavities.

The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serum albumin (HSA) media. In buffered aqueous solution the polymer shows dual emission corresponding to the monomer and the excimer of pyrene moiety. The relative intensity of the monomer to the excimer emission shows interesting variation with the addition of BSA and HSA and is indicative of significant interaction of these albumin proteins with the polymer. The binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands. Attempt has been made to determine the micropolarities of the protein microenvironments from a comparison of the variation of the monomer to excimer relative fluorescence intensities of the probe in water-dioxane mixtures with varying composition.

Energetics of formation of the intermediate during the photocyclisation of phenylbenzoquinone (PBQ) to 2hydroxydibenzofuran (HDBF) in methanol solvent has been investigated by employing the time-resolved photoacoustic calorimetric (TRPAC) technique. The study, in conjugation with the nanosecond/microsecond fla sh photolytic observations, confirms the formation of a long lived intermediate during the photocyclisation reaction. TRPAC result and semi-empirical (AMI and PM3) calculations suggest that the intermediate is a biradical.

The binding interaction of a potential nervous system stimulant, 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]-quinolizine (AODIQ), with calf-thymus DNA (ctDNA) has been explored thoroughly. The modified photophysics of the fluorescent molecule within the microheterogeneous biomacromolecular system has been exploited to divulge the drug-DNA binding interaction. The absorption and various fluorometric measurements together with the fluorescence quenching, urea-induced denaturation study, circular dichroism and DNA-melting studies unequivocally ascertain the mode of binding of the drug with the DNA to be groove binding. Corroborating the experimental observations, molecular docking simulation projects the minor groove of the biomacromolecule to be the site of binding. Further experiments have revealed that dissociation of the drug from the drug-DNA complex can be achieved by the detergent sequestration method. Besides providing an insight into the drug-DNA interaction the work also de...