“…This was in contrast to the conclusion of Visser et al in their study of exciplexes between DMABN and 1,4-dioxane solvent, which were ascribed to 1:1 solute−solvent twisted exciplexes …”
Section: Referencescontrasting
confidence: 99%
“…A more direct technique, transient microwave conductivity, has been used by Fessenden et al and Visser et al to measure excited-state dipole moments including those of some exciplexes. As in the case of the electrooptical technique, dipole moments tend to be lower than those estimated from solvatochromic shifts.…”
A transient dc photocurrent technique was used to measure the dipole moments of exciplexes formed between
the electronically excited electron acceptors 9,10-dicyanoanthracene (DCA) or 2,6,9,10-tetracyanoanthracene
(TCA) and methyl-substituted benzene (SB) donors. For either acceptor in benzene solution, exciplex dipole
moments increase with decreasing donor oxidation potential until a maximum dipole moment of ca. 11 D is
reached. A similar trend has been previously observed using other techniques, but the maximum dipole
moments that we report are substantially less than is usually assumed for such systems. Mutual ion polarization
is the likely cause of this difference, and a simple equation for estimating its effects is provided.
“…This was in contrast to the conclusion of Visser et al in their study of exciplexes between DMABN and 1,4-dioxane solvent, which were ascribed to 1:1 solute−solvent twisted exciplexes …”
Section: Referencescontrasting
confidence: 99%
“…A more direct technique, transient microwave conductivity, has been used by Fessenden et al and Visser et al to measure excited-state dipole moments including those of some exciplexes. As in the case of the electrooptical technique, dipole moments tend to be lower than those estimated from solvatochromic shifts.…”
A transient dc photocurrent technique was used to measure the dipole moments of exciplexes formed between
the electronically excited electron acceptors 9,10-dicyanoanthracene (DCA) or 2,6,9,10-tetracyanoanthracene
(TCA) and methyl-substituted benzene (SB) donors. For either acceptor in benzene solution, exciplex dipole
moments increase with decreasing donor oxidation potential until a maximum dipole moment of ca. 11 D is
reached. A similar trend has been previously observed using other techniques, but the maximum dipole
moments that we report are substantially less than is usually assumed for such systems. Mutual ion polarization
is the likely cause of this difference, and a simple equation for estimating its effects is provided.
“…The dipole moment is determined by experiment in the range between 5.8 D (electrooptical measurements) and 11.4 D (solvatochromic results) . The reliable transient electron loss method yields 9.11 D, which is in excellent agreement with the STEOM-CCSD value of 9.16 D. The CASPT2 dipole moment of 7.6 D 12 is located at the lower, and the DFT/SCI value of 11.5 D 15 at the upper limit, of the experimental range. In general, also the efficient DFT/SCI method yields comparable results: Both the exitation energies (4.05 eV (S 1 ) and 4.56 eV (S 2 )) and oscillator strengths (0.027 (S 1 ) and 0.658 (S 2 )) are of high quality.…”
Section: Resultsmentioning
confidence: 55%
“…Several models for the explanation of this unusual behavior have been subsequently proposed, but the photophysics of this phenomenon has most frequently been discussed within the twisted intramolecular charge transfer (TICT) model by Z. R. Grabowski and co-workers. , In this model, the highly polar charge transfer excited state is formed by internal twisting of the donor (dimethylamino subunit) relatively to the acceptor (benzonitrile subunit) in the excited state. Nevertheless, several other models, as complexation or formation of exciplexes with the solvent − or solvent-induced vibronic coupling between the energetically close lying first singlet states, , are still discussed as possible explanations. 1 Structures of ABN (left) and DMABN (right).…”
The excited states of 4-(N,N-dimethylamino)benzonitrile (DMABN) and 4-aminobenzonitrile (ABN) are characterized by the similarity transformed equation-of-motion coupled-cluster method with single and double excitations (STEOM-CCSD). The long wavelength band of DMABN is assigned by STEOM-CCSD to an emission of a geometrically relaxed twisted intramolecular charge transfer (TICT) state. In contrast, no lowering in total energy upon twisting is found in ABN. The different behavior of the TICT states in ABN and DMABN can quite clearly be understood from the behavior upon twisting of the correlated ionization potentials and electron affinities from IP/EA-EOM-CCSD results that are obtained as a side product of STEOM-CCSD calculations. Inclusion of electron correlation is found to be crucial however, as the effect is largely lost at the Hartree-Fock (Koopmans') level of accuracy. The STEOM-CCSD results are similar to results from DFT/SCI calculations. In general they also agree well with results from previous CASPT2 calculations and experimental data, where available. The crucial behavior of the energy of the TICT states upon rotation of the amino group in ABN and DMABN differs markedly however, between STEOM-CCSD and CASPT2. Whereas in STEOM-CCSD upon twisting we find the expected lowering for the TICT state in DMABN and rise in energy for ABN, this is not the case in CASPT2. Previous benchmarks indicate that CASPT2 may have difficulties describing differential dynamical correlation associated with transitions from lone pair orbitals, and we think therefore that the results at the STEOM-CCSD and DFT/SCI levels may be more accurate for this aspect of the problem.
“…Description of this specific solute−solvent interaction as a three-electron bond to the solvent lone pair was also suggested by Wang . Later, the group of Varma, continuing to support the exciplex hypothesis, withdrew from the concept of an intermediate planar exciplex 9 Scheme of terms in the exciplex with the solvent, as proposed by Varma et al Lone pairs of the solute molecule, n m , and of the solvent, n s , interact, which results in a splitting (λ 1 , λ 2 ).…”
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