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

Abstract

946J. Am. Chem. SOC. diffusing carbonium ions by acetonitrile solvent followed by hydrolysis (the Ritter reaction starting from an unactivated C-H bond). The other minor byproducts including those derived from photooxidation of the tetra-n-butylammonium cations and the acetonitrile solvent as well as a small percentage of the epimerization product arise from freely diffusing intermediate radicals.Not shown in Scheme I11 are the processes involving reoxidation of the reduced [or photoreduced] polyoxotungstates. Reoxidation can be facilitated by (1) reaction with O2 and protons, evolved from the dehydrogenation reactions, to form H 2 0 , (2) reaction solely with protons to form H2, or (3) in some circumstances, by reaction with other oxidants. These processes, although peripheral to the novel chemistry in the complex redox processes which we have elaborated in this paper, are nevertheless significant for they limit the overall rate of catalytic turnover. 1992,114,946-953The substantial degree to which the first and second redox potentials, protonation states, and other characteristics of the polyoxometalates that affect the relative rates of the key processes in Scheme I11 and analogous processes in other reactions can be systematically altered through rational syntheses of polyoxometalates suggests potential applications of these complex inorganic molecules to transformations of organic materials in synthesis and various technologies.Acknowledgment. We thank the National Science Foundation (Grant CHE-9022317) for support.Registry No. cis-1, 1579-21-1; trans-1, 16021-08-2; 2, 13837-12-2; 3, 062, 110294-54-7; Q4W10032,68109-03-5; Na4Wl,OJ2, 126752-51-0; D2, 7782-39-0; cis-decalin, 493-01-6; trans-decalin, 493-02-7.1196-55-0; DTBO, 1876-22-8; Q3PW12040, 53749-37-4; (NH4) Abstract The luminescence properties of 2,3-naphthalimides have been studied using picosecond and nanosecond spectroscopies. In acetonitrile solution N-phenyl-2,3-naphthalimide (3) 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 ari...

Solvent and temperature effects on the deactivation pathways of excited ion pairs produced via photoinduced proton transfer

“…13 Singlet lifetimes were measured by excitation with a B. M. Industries frequencytripled Nd-YAG laser (pulse duration 30 ps FWHM), using the experimental set-up already described. 15 …”

Temperature-Dependent Behavior of the Dual Fluorescence of 2-(3-Fluorophenyl)-2,3-dihydro-1H-benzo[f]isoindole-1,3-dione

“…Effectively, the fluorescence of both SW* and LW* states of 1 decays on a relatively long time scale at low temperature, and no reversible process has been observed between the two excited states. The same behavior was found for 2 in highly viscous media [11]. This led us to use Scheme 2, which was already discussed in our previous articles, to explain the behavior of 1 in GTA at low temperature.…”

“…Observations made with the unsubstituted molecule 2 indicated [11] that, under certain conditions, dual luminescence can be observed, with an emission at long-wavelength (named hereafter longwavelength (LW) fluorescence), which appears well-separated and red-shifted from the so-called short-wavelength (SW) emission. These two emissions differ from each other not only by their position, but also by their decay.…”

“…These two emissions differ from each other not only by their position, but also by their decay. When no SW* 3 LW* transformation is observed, as in the case of 2 [11], the relaxed SW* emission decays in the picosecond time range and the LW* emission in the nanosecond time scale. This behavior differs i) from the usual case [12 ± 17], where the SW* state is the precursor of the LW* state and also ii) from the classical excimer formation [18 ± 21].…”

“…In the viscous GTA medium, a slight decrease in temperature induces a large increase in viscosity of the medium. We have reported in previous publications the time-resolved fluorescence decay of 1 [10] (in GTA) and 2 [11] (in various glycerol-EtOH mixtures) at low temperature and have shown their different behaviors in comparison to that in MeCN. The decrease of the k 1 and k À1 with temperature results from the increased steric hindrance to the rotation of the N-phenyl ring in both SW* 3 LW* and LW* 3 SW* steps.…”