Comparison of exciplex generation under optical and X-ray excitation

Abstract

Exciplex generation under optical and X-ray excitation in identical conditions is experimentally compared using a specially chosen model donor-acceptor system, anthracene (electron acceptor) and N,N-dimethylaniline (electron donor) in non-polar solution, and the results are analyzed and interpreted based on analytically calculated luminescence quantum yields. Calculations are performed on the basis of kinetic equations for multistage schemes of bulk exciplex production reaction under optical excitation and combination of bulk and geminate reactions of radical ion pairs under X-ray excitation. These results explain the earlier experimentally found difference in the ratio of the quantum yields of exciplexes and excited electron acceptors (exciplex generation efficiency) and the corresponding change in the exciplex generation efficiency under X-irradiation as compared to the reaction under optical excitation.

X-ray Generated Recombination Exciplexes of Substituted Diphenylacetylenes with Tertiary Amines: A Versatile Experimental Vehicle for Targeted Creation of Deep-Blue Electroluminescent Systems

“…The excited states of diphenylacetylenes and DMA are generated primarily by direct energy transfer from excited solvent molecules forming in abundance under X-irradiation in n -alkanes (for DDC fluorescence quantum yield is 0.0055, τ F = 4.2 ns) . If desired, this emission channel can be completely suppressed under X-irradiation by taking an alkane solvent with zero quantum yield of fluorescence, for example, isooctane (2,2,4-trimethylpentane), and it will be eliminated if radical ions recombining into exciplexes are generated directly by charge injection.…”

“…It should be stressed that the ordering of radiation-induced emission efficiency observed for the three Meq 3 coincided with the ordering of their electroluminescence efficiencies, which reflects the similarity between electrogenerated and radiation-induced luminescence . Regarding radiation-generated exciplex emission, for luminophores that produce both substantial intrinsic emission and exciplex emission, for example, anthracene in mixtures with DMA , it is possible to use the intrinsic emission as an internal reference for the number of excited states and normalize exciplex emission to it, ,, but it is only useful for comparing the effects of different excitation sources (optical vs radiation) on the same system and not to compare different systems to each other.…”

“…For most spectra with well-separated exciplex and intrinsic emission bands this was done directly on experimental spectra, like spectra (1) and (2) from Figure A. For the mixtures of 1OMe or 3OMe with DMA , where the two emission bands substantially overlap (Figures SI3.6 and SI3.8 of the SI), the spectra were decomposed into the sum of spectra of the individual emission components using the approach of refs and . The relevant details are given in SI section 3.8.…”

Recombination of X-ray-Generated Radical Ion Pairs in Alkane Solution Assembles Optically Inaccessible Exciplexes from a Series of Perfluorinated para-Oligophenylenes with N,N-Dimethylaniline

“…The diphenylacetylene-DMA exciplex, which could be generated only via the recombination channel, turned out to be the most convenient vehicle to create a number of related diphenylacetylene-based systems with systematically varied properties [4], develop methods to exploit the magnetic field sensitivity of the recombination [5] and estimate the exciplex lifetime [6]. A theory was developed to juxtapose the optical and X-ray generation of the exciplexes, augmenting the reaction scheme of radiation chemistry with the relevant processes leading to the experimentally observed exciplex formation [7]. The possibility to obtain unrestricted experimental data potentially opens vast opportunities for quantum chemical studies of exciplexes that require the most advanced methods to faithfully describe weakly bound, excited complexes of relatively large molecules.…”

“…The radiation chemistry processes used in this work do not involve such a delicate balance of states in equilibrium and are irreversible, with the exciplex emission band simply inheriting the magnetic field sensitivity of the recombination of spin-correlated radical ion pairs in a low-polarity alkane liquid. The key elements of this approach in producing and studying exciplexes have been described earlier, in a series of our publications [1][2][3][4][5][6][7], to which the reader is referred regarding details and a historical overview. In this work, we shall focus on a specific set of new, promising exciplex-forming systems, quoting necessary details only when they are required for describing a particular experiment as the story unfolds.…”