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

Influence of molecular design on the morphology of nanoparticles formed from 1-alkyl-6-alkoxy-quinolinium cations and 4-sulfonatocalix[n]arenes

In order to reveal the influence of the guest molecular structure, the interactions between 4-sulfonatocalix[n]arene (SCXn) cavitands (n = 4 or 6) and two series of quinolinium derivatives were studied in neutral aqueous solutions at 298 K. For this, the long alkyl chain of the quinoliniums was attached either to the heterocyclic nitrogen (CmC1OQ+ m = 10, 12, or 14) or to the oxygen located in position 6 of the aromatic system (C1CmOQ+ m = 8, 10, or 12). All the quinolinium derivatives self-assembled with SCXn into nanoparticles (NP), whose size, zeta potential and composition were determined over a large molar mixing ratio range. Isothermal titration calorimetry showed that host-guest binding assisted the formation of negatively charged NPs in exothermic processes. The enthalpy gain in these associations significantly increased with the lengthening of the 1-alkyl group but was insensitive to the size of the SCXn macrocycle. The morphology of NPs was studied by cryo-TEM method. CmC1OQ+ organization with SCXn led to spherical NPs without regular inner structure. In contrast, C1CmOQ+-SCXn nanoaggregates usually had various shapes and the original morphologies exhibited lamellar domains with ~3 nm layer thickness. The different orientation of CmC1OQ+ and C1CmOQ+ in the cavitand was proposed to rationalize the morphological alterations

Use of a photoreversible fulgide as an actinometer in one- and two-laser experiments

The photoreversible fulgide Aberchrome-540 has been tested and developed as an actinometer for one- and two-laser experiments. In the former, the technique allows the determination of extinction coefficients for short-lived reaction intermediates by a method that requires substantially fewer assumptions than other techniques in the literature. In the case of stepwise two-photon processes, the Aberchrome-540 method allows the determination of quantum yields for photoreactions of short-lived reaction intermediates. For this particular application the technique is the only one of its kind.NRC publication: Ye

Laser photolysis studies of transient processes in the photoreduction of naphthalimides by aliphatic amines

The photoreduction of N-phenyl- 1,8-naphthalimide and N-phenyl-2,3-naphthalimideb y aliphatic amines has been studied by laser flash photolysis with transient absorption and transient conductivity methods in different solvents. Analysis of transient time profiles establish for most systems the occurrence of a fast primary and a slower secondary reduction process. Primary reduction is ascribed to the reaction between a triplet naphthalimide and an amine, while secondary reduction is assigned to the reaction of an amine-derived \alpha-aminoalkyl radical with a ground-state naphthalimide molecule. In polar solvents, with aliphatic amines both primary and secondary reductions proceed by electron transfer. In solvents of intermediate polarity, hydrogen atom transfer (primary reduction) is succeeded by electron transfer (secondary reduction). Finally, in nonpolar solvents, only primary reduction by hydrogen atom transfer is found to occur. Rate constants are obtained for most of these processes by computer modeling of the transient time profiles. In polar solvents, reaction AH(2)+ + AH(2) - AH + AH(3)+ (where AH(2) and AH are the amine and \alpha-aminoalkyl radical, respectively) is a key reaction in which the \alpha-aminoalkyl radical is formed. Its rate constant is found to decrease by more than 4 orders of magnitudes when AH(2) varies from tertiary, through secondary, to primary amine. This is explained by the significant change in the dissociation energy of the C-H bond in the \alpha-position to the nitrogen. The electron transfer between the \alpha-aminoalkyl radical and the naphthalimide molecule is found to occur in polar solvents with a rate close to the diffusion controlled limit, whatever the type of the aliphatic amines