Experimental and Calculated Spectra of π-Stacked Mild Charge-Transfer Complexes: Jet-Cooled Perylene·(Tetrachloroethene)n, n = 1,2

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Using the stimulated-emission-pumping/resonant 2-photon ionization (SEP-R2PI) method, we have determined accurate intermolecular dissociation energies D of supersonic jet-cooled intermolecular complexes of 1-naphthol (1NpOH) with alkanes, 1NpOH·S, with S = methane, ethane, propane, and n-butane. Experimentally, the smaller alkanes form a single minimum-energy structure, while 1-naphthol·n-butane forms three different isomers. The ground-state dissociation energies D(S) for the complexes with propane and n-butane (isomers A and B) were bracketed within ±0.5%, being 16.71 ± 0.08 kJ/mol for S = propane and 20.5 ± 0.1 kJ/mol for isomer A and 20.2 ± 0.1 kJ/mol for isomer B of n-butane. All 1NpOH·S complexes measured previously exhibit a clear dissociation threshold in their hot-band detected SEP-R2PI spectra, but weak SEP-R2PI bands are observed above the putative dissociation onset for the methane and ethane complexes. We attribute these bands to long-lived complexes that retain energy in rotation-type intermolecular vibrations, which couple only weakly to the dissociation coordinates. Accounting for this, we find dissociation energies of D(S) = 7.98 ± 0.55 kJ/mol (±7%) for S = methane and 14.5 ± 0.28 kJ/mol (±2%) for S = ethane. The D values increase by only 1% upon S → S excitation of 1-naphthol. The dispersion-corrected density functional theory methods B97-D3, B3LYP-D3, and ωB97X-D predict that the n-alkanes bind dispersively to the naphthalene "Face." The assignment of the complexes to Face structures is supported by the small spectral shifts of the S → S electronic origins, which range from +0.5 to -15 cm. Agreement with the calculated dissociation energies D(S) is quite uneven, the B97-D3 values agree within 5% for propane and n-butane, but differ by up to 20% for methane and ethane. The ωB97X-D method shows good agreement for methane and ethane but overestimates the D(S) values for the larger n-alkanes by up to 20%. The agreement of the B3LYP-D3 D values is intermediate between the other two methods.

Section: B Theoretical Methodsmentioning

confidence: 99%

Intermolecular dissociation energies of 1-naphthol·n-alkane complexes

Knochenmuss

Maity

Balmer

et al. 2018

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“…37 The latter two methods gave good results in a study of large π-stacked complexes. 38,39 The earlier D2 dispersion-correction method of Grimme corrects the DFT method using atompairwise C (6) ij /R 6 ij atom-atom interaction potentials, with C (6) ij coefficients that depend on the pair of atoms i and j. 40 The D2 model will be used to calculated per-atom contributions to the dispersion interaction in section IV.B.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Intermolecular dissociation energies of dispersively bound 1-naphthol⋅cycloalkane complexes

Maity

Ottiger

Balmer

et al. 2016

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“…The latter two methods have given good results in studies of large π-stacked complexes. 62,63 All structure optimizations were unconstrained. The binding energies D e were calculated by subtracting the total energies of trans-1-naphthol and of the solvent molecule S -both optimized at their respective isolated-molecule geometries -from the total energy of the 1-naphthol·S complex at its optimized minimum-energy geometry.…”

Section: B Experimentalmentioning

confidence: 99%

Intermolecular dissociation energies of hydrogen-bonded 1-naphthol complexes

Knochenmuss

Sinha

Poblotzki

et al. 2018

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We have measured the intermolecular dissociation energies D 0 of supersonically cooled 1-naphthol (1NpOH) complexes with the solvents S=furan, thiophene, 2,5-dimethylfuran and tetrahydrofuran. The naphthol OH forms non-classical H-bonds to the aromatic π-electrons of furan, thiophene and 2,5dimethylfuran, and a classical H-bond to the tetrahydrofuran O atom. Using the stimulated-emission pumping resonant two-photon ionization (SEP-R2PI) method, the ground-state D 0 (S 0 ) values were bracketed as 21.8 ± 0.3 kJ/mol for furan, 26.6 ± 0.6 kJ/mol for thiophene, 36.5 ± 2.3 kJ/mol for 2,5-dimethylfuran and 37.6 ± 1.3 kJ/mol for tetrahydrofuran. The dispersion-corrected density functional theory (DFT-D) methods B97-D3, B3LYP-D3 (using the def2-TZVPP basis set) and ωB97X-D [using the 6-311++G(d,p) basis set] predict that the H-bonded (Edge) isomers are more stable than the Face isomers bound by dispersion; experimentally, we only observe Edge isomers. We compare the calculated and experimental D 0 values and extend the comparison to the previously measured 1NpOH complexes with cyclopropane, benzene, water, alcohols and cyclic ethers. The dissociation energies of the nonclassically H-bonded complexes increase roughly linearly with the average polarizability of the solvent,ᾱ(S). In contrast, the D 0 values of the classically H-bonded complexes are larger, increase more rapidly at lowᾱ(S) but saturate for largeᾱ(S). The calculated D 0 (S 0 ) values for the cyclopropane, benzene, furan and tetrahydrofuran complexes agree with experiment to within 1 kJ/mol, those of thiophene and 2,5-dimethylfuran are ∼ 3 kJ/mol smaller than experiment. The B3LYP-D3 calculated D 0 values exhibit the lowest mean absolute deviation (MAD) relative to experiment (MAD=1.7 kJ/mol), the B97-D3 and ωB97X-D MADs are 2.2 and 2.6 kJ/mol, respectively.