Kísérleti és elméleti kutatások fotofizikai folyamatok oldószerfüggésének általánosabb leírására = Experimental and theoretical examinations for better understanding of solvent dependence of photophysical processes

A zárójelentésben bemutatott kutatásokban több modellrendszeren vizsgáltuk az oldószer különböző tulajdonságainak - így polaritásának, viszkozitásának és hidrogénhíd-kötő képességének - hatását a fotofizikai rendszer viselkedésére. A polaritás-függést a Lippert-Mataga formalizmussal értelmeztük, az effektus segítségével meg tudtuk határozni több 4-amino-benzonitril származék, az N-fenil-pirol, a 4-(dimetilamino)-piridin és az utóbbi molekula hidrogénhidas komplexének gerjesztett állapotú dipólusmomentumát is. A komlexált molekula esetében az oldószer polaritásának növelése a gerjesztett állapot jellegének megváltozását indukálta. A gerjesztett állapotú folyamatok termodinamikájának és kinetikájának kvantitatív elemzése lehetővé tette a hasonló jellegű, alapállapotban is lejátszódó folyamatok sebességének becslését, valamint az eredményeink alapján felmerült annak a lehetősége is, hogy a hidrogénhidas komplexképződés egyáltalán nem tekinthető elemi reakciónak. Megmutattuk, hogy az oldat viszkozitása jelentősen befolyásolhatja a gerjesztett állapotú folyamatokat, egyrészt a nagy amplitúdójú relaxációs mozgások gátlásával, másreszt az oldószerburok átrendeződésének fékezésével, ennek eredményeképpen szélsőségesebb esetekben meglepő kinetikai és fotofizikai jelenségeket is tapasztalhatunk. | In our examinations presented here, the properties of several model systems are elucidated as the function of solvent polarity, viscosity as well as hydrogen bond donor properties. The influence of the polarity was described by the Lippert-Mataga equation, and the excited state dipole moments were calculated for 4-aminobenzonitril derivatives, for N-phenylpyrol, for 4-(dimethylamino)pyridine and its hydrogen-bond complexed derivative. The increase of the solvent polarity induces a change in the nature of the intramolecular charge transfer singlet excited species in the last case. Quantitative analysis of the thermodynamics and kinetics of the excited state hydrogen-bond forming processes made possible to estimate rate of the analogous ground-state reactions, as well as to suppose the assumption that the reaction in question is not an elementary process at all. The viscosity of the solvent was shown a crucial factor influencing the excited state processes by hindering the large amplitude intramolecular relaxation motions, as well as by slowing down the solvent relaxation processes causing in extreme cases surprising kinetic and photophysical feature

Influence of geometry on the emitting properties of 2,3-naphthalimides

The luminescence properties of 2,3-naphthalimides have been studied using picosecond and nanosecond spectroscopies. In acetonitrile solution N-phenyl-2,3-naphthalimid(e3 ) is found to emit dual fluorescence with emission maxima at 385 and 490 nm, respectively. The short-wavelength emission corresponds to the known fluorescence of the naphthalimides and is demonstrated for 3 to originate from a molecular conformation in which the phenyl substituent and the naphthalimide skeleton are orthogonal to each other. The long-wavelength emission is assumed to originate from a singlet excited state formed by a ca. 90° rotation of the phenyl group so that the two moieties are coplanar. Only a small dipole moment change is found between this excited state and the ground state. Only short-wavelength emission is observed with a lifetime in the nanosecond range as in the case of 1 and 2 when phenyl rotation is blocked with a bulky ortho tert-butyl group (compound 4). Increasing the viscosity of a glycerol/ethanol medium enhances both the efficiency and the lifetime of the short-wavelength emission of 3. It appears that at 77 K the emission originates directly from the Franck-Condon state. At room temperature, the other two emitting species are shown to arise from the Franck-Condon state by competitive intramolecular geometrical relaxation processes. Structures 5 and 6 are tentatively put forward to explain the formation of naphthazepinedione 8 by a 2 \pi + 2 \pi photochemical cycloaddition reaction

Crystal and molecular structure ofN-phenyl substituted 1,2-, 2,3- and 1,8-naphthalimides

The three structures were solved by direct methods and refined by full-matrix least-squares procedure. 2-phenyl-1 H-benz[f]isoindole-1,3(2 H)-dione, (compound 1): orthorhombic, space group Pcab, a = 7.618(1) Angstrom, b = 11.717(2) Angstrom, c = 28.540(4) Angstrom, V = 2547.4(7) Angstrom(3), Z = 8 and d = 1.425 Mg m(-3), R = 0.038 (Rw = 0.038) for 190 parameters and 820 observations with I > 2.5 sigma(I). 2-phenyl-1 H-benz[e]isoindole-1,3 (2 H)-dione (compound 2): orthorhombic, space group Pc2(1)b, a = 6.7042(9) Angstrom, b = 7.4589(9) Angstrom, c = 26.441(7) Angstrom, V = 1322.4(4) Angstrom(3), Z = 4 and d = 1.373 Mg m(-3), R = 0.037 (Rw = 0.032) for 190 parameters and 1186 observations with I > 3 sigma(I). 2-phenyl-1 H-benz[de]isoquinoline-1,3(2 H)-dione (compound 3): monoclinic, space group C2/c, a = 13.501(3) Angstrom, b = 13.212(4) Angstrom, c = 8.305(2) Angstrom, beta = 116.24(2 degrees, V = 1329(9) Angstrom(3), Z = 4, and d = 1.366 Mg m(-3), R = 0.038 (Rw = 0.033) for 71 parameters and 754 observations with I > 3 sigma(I). The plane of the N-phenyl substituent has an axis which lies in the plane of the naphthalimide part and passes by the carbon atom bound to the nitrogen atom and by the carbon in para position. It makes a dihedral angle with the plane of the naphthalimide moiety of 59.2 degrees, 46.5 degrees and 69.4 degrees for the compounds 1, 2 and 3 respectively. This difference in geometry between the three molecules brings new insights into their spectroscopic properties

Application of density functional theory to the vibrational characterization of transitional metal complexes

Bibliography: p. 144-148