Internal Conversion in 1-Aminonaphthalenes. Influence of Amino Twist Angle

Abstract

With the 1-aminonaphthalenes 1N5 and 1DMAN a fast radiationless process occurs in n-hexane, diethyl ether, and acetonitrile, which is shown to be internal conversion (IC). The IC reaction is slower with 1N4 and much less efficient with 1MAN and 1AN. This IC process is thermally activated and slows down with increasing solvent polarity, due to a larger IC activation energy. In the ground state S0, the amino twist angle θ relative to the naphthalene plane increases in the order 1MAN, 1AN, 1N4, 1N5, 1DMAN, as derived from absorption and fluorescence spectra, 1H NMR spectra, ground-state dipole moments, and ab initio calculations. For the five 1-aminonaphthalenes in the equilibrated S1 state, the twist angle and the radiative rate constant have similar values. The different IC efficiences of these molecules are therefore determined by the structural differences (amino twist angle) between S1 and S0. A correlation is found between the IC efficiency in these molecules and the twist angle θ. The IC process to S0 starts from the equilibrated S1 state, which is vibronically coupled with S2 due to a small energy gap ΔE(S1,S2). It is therefore concluded that the extent of vibronic coupling and the magnitude of the twist angle θ are the determining factors in the IC process.

Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

“…The photophysical properties of organic compounds with electron-donor and electron-acceptor substituents have been widely studied recently [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. They are of interest in connection with their possible application as organic light-emitting diodes in color graphical displays [6], fluorescent labels and visualizing agents in biological systems [7,8], and also owing to their nonlinear optical properties [9, 10] (high quadratic polarizability β).…”

“…The quantum yield of the dye DCM increases linearly from 0.08 in toluene to 0.80 in DMSO. For DCMF3 and DCMF7, which differ from DCM only by the presence of strong electron-acceptor CF 3 The absorption and fluorescence spectra of DCMF3 in n-propanol at 293 K and 77 K are shown in Fig. 4.…”

“…Absorption spectra (1, 2) and fluorescence spectra(3,4) of DCMF3 in n-propanol at room temperature(2,4) and at 77 K (1, 3).…”

Fluorescence Monitoring of Curing Process and Water Accessibility at Glass Fiber/Epoxy Interphase on Composite Materials

“…In general, fluorophores that, following absorption of excitation light undergo nonradiative decay by intramolecular twisting or torsional motions such as aminonaphtalenes [26] like dansyl derivatives [27], show a viscosity-dependent fluorescence [16,28]. When epoxy curing takes place, the motion of the fluorophores becomes progressively more inhibited by increasing viscosity of the polymer.…”

Efficient ultraviolet-light energy dissipation by an aromatic ketone

“…The results demonstrate that this aromatic ketone efficiently dissipates UV-light energy due to the extremely short lifetime of its triplet excited state, which rapidly decays back to the ground state. For comparison, the photobehaviour of analogous compounds, benzil (BZ) and 4,4 0 -dimethoxybenzil (DMBZ), is included.…”