Search

The quantum yield O(e aq ) of photoejected electrons from aromatic carboxylate anions in aqueous solutions (pH 9.5 – 12.3) appreciably increases with increasing excitation energy; for example, O(e aq ) for benzoate is 0.0025 for the S 1 state (excitation at 254 nm) and 0.0048 for the S 2 state (excitation at 214 nm). The O(e aq ) value also increases with the number of CH 2 groups separating the phenyl and carboxylate groups; for example, for phenylbutyrate O(e aq ) is 0.05 for the S 1 state and 0.010 for the S 2 state. Furthermore, increases of O(e aq ) are linked with decreases in the quantum yield of fluorescence. In order to evaluate a possible consumption of the photoejected electrons by the ground state carboxylates, the rate constants k (e aq + substrate) for the reaction of solvated electrons with the corresponding substrates were determined.

Exciplex formation of triethylamine with ethanol and with deuterated ethanol at low alcohol concentrations in hydrocarbon solutions is shown by steady state and time-resolved fluorescence spectroscopy. The observed spectra and the decay kinetics show the appearance of three exciplex structures which can be discriminated by temperature and deuterium isotope effects. The spectrum of the primarily formed 1:1 heterodimer overlaps significantly with the monomer spectrum (spectral shift is 800 cm −1 ) and equivalent associations are found with tetrahydrofuran. The photophysical parameters change only slightly on complexation. Two further exciplex emissions with large spectral shifts compared with the monomer (4500 cm −1 and 9000 cm −1 ) arise at ethanol concentrations above 0.02 M, together with a diminution of the quantum yield. Complexation with non-deuterated ethanol leads primarily to high energy emissive structures and equilibrium is attained, as they decay with a common lifetime. Deuteration of ethanol results in a stabilization of the lowest energy exciplex, which is populated irreversibly. Exciplex structures are discussed, with reference to ab inition model calculations.

Fluorescence spectra, quantum yields and lifetimes are comparatively studied for aniline, N,N -dimethylaniline (DMA) and some further alkylsubstituted and rigid aniline derivatives in various solvents. A good correlation of Stokes shift with macroscopic solvent parameters is found for DMA but not for aniline. General and specific solvent effects are distinguished by studying the functional dependence of various spectroscopic and photophysical parameters on the polar co-solvent concentration in binary solvent mixtures. Excited state complexation of primary and secondary amines with alcohols is demonstrated by the double-exponential decay of the monomer fluorescence and the grow-in of exciplex emission found in aniline—ethanol— n -hexane ternary systems. Exciplex formation is attributed to solvent—donor hydrogen bonding and primarily causes enhanced intersystem crossing compared with that in the free molecule, an effect also evoked by N -methylation. Non-specific long-range interactions give rise to a general reduction in the non-radiative deactivation rate, with the exception of o,o′ -dimethyl-substituted anilines, for which an increase in this rate was found as the bulk becomes polar.

The effects of the excitation wavelength on the quantum yields Q(eaq−) and QF of electron ejection and fluorescence respectively were measured for 4-cyano-N,N-dimethylaniline (CDMA) and related compounds in aqueous solutions. In the case of CDMA no electron ejection was found for excitation of the long-wavelength (1La, 1Lb) band system. At shorter wavelengths (λexc

Two primary photoreactions were observed for derivatives of 2-phenylindian-1,3-dione in various solvents: (1) cleavage of the hydrogen atom in the α position to both keto groups resulting in the formation of 2-arylindan-1,3-dion-2-yl radicals; (2) photoisomerization to benzylidenephthalides as a result of bond rupture via a Norrish type I mechanism. Both processes are possible with different quantum yields from the diketo form (in apolar solvents), from the enol form (in alcohols) and from the enolate form (in alkaline water).

The yields of fluorescence at 295 and 77 K and of phosphorescence at 77 K of phenol and anisole were determined in solvents of different polarities (hydrocarbons, ether, ethanol). Also intersystem crossing yields are reported for phenol and anisole in cyclohexane solution at 295 K. The data show that a non-radiative process, different from intersystem crossing, competes with the decay of S 1 phenol in liquid hydrocarbons. The nature of this deactivation pathway is discussed.