The Spectroscopy and Photophysics of π Hydrogen‐BondedComplexes: Benzene–CHCl₃

Abstract

A vibronic level study of the spectroscopy and photophysics of the C6H6–CHCl3 complex has been carried out using a combination of laser-induced fluorescence and resonant two-photon ionization (R2PI). In C6H6-CHCl3, the S1–S0 origin remains forbidden while the 1610 transition is weakly induced. Neither 610 nor 1610 are split by the presence of the CHCl3 molecule. On this basis, a C3vstructure is deduced for the complex, placing CHCl3 on the six-fold axis of benzene. The large blue-shift of the complex’s absorption relative to benzene (+178 cm–1) and the efficient fragmentation of the complex following one-color R2PI reflect a hydrogen-bonded orientation for CHCl3 relative to benzene’ π cloud. Dispersed fluorescence scans place a firm upper bound on the ground state binding energy of the complex of 2,024 cm–1. Both the 61and 61 11 levels do not dissociate on the time-scale of the S1 fluorescence and show evidence of extensive state mixing with van der Waals’ levels primarily built on the 00 level of benzene. The C6H6–(CHCl3)2 cluster shows extensive intermolecular structure beginning at +84 cm–1, a strong origin transition, and splitting of 61. A structure which places both CHCl3 molecules on the same side of the benzene ring is suggested on this basis. The vibronic level scheme used to deduce the structure of C6H6–CHCl3 is tested against previous data on other C6H6–X complexes. The scheme is found to be capable, in favorable cases, of deducing the structures of C6H6–X complexes based purely on vibronic level data. Finally, the results on C6H6–CHCl3 are compared with those on C6H6–HCl and C6H6-H2O to evaluate the characteristics of the n hydrogen bond.

Blue-Shift in the Frequencies of the CH Stretches of Chloro- and Fluoroform Induced by C–H...π Hydrogen Bonding with Benzene Derivatives: the Influence of Electron Donating and Withdrawing Substituents

“…A similar vdW progression with comparable blue-shifts has been reported by Gotch et al for the 1 : 2 cluster of the Bz/Cf system [22]. A similar vdW progression with comparable blue-shifts has been reported by Gotch et al for the 1 : 2 cluster of the Bz/Cf system [22].…”

“…A·(Ff) 2 Fb, Fb-d5 296 Bz, Bz-d6 240, 410 To-d8 435 PX, PX-d10 390 and larger clusters [22]. We diminished these contributions considerably by decreasing the Cf concentration and improving the cooling.…”

A theoretical study of methylation and CH/π interactions in DNA intercalation: methylated 1,10-phenanthroline in adenine–thymine base pairs

“…In addition, CH/p contacts of the methyl group of thymine or the backbone sugars with DNA or proteins have been also described. [73][74][75] Moreover, several theoretical calculations 8,22,23,31,[33][34][35]37 and gas phase spectroscopic measurements of the CH/p interactions have been reported 22,23,33,35,[76][77][78] and it is expected that such CH/p interactions are able to play an important role in drug design.…”

Experimental and theoretical determination of the accurate interaction energies in benzene–halomethane: the unique nature of the activated CH/π interaction of haloalkanes

“…9,13 As for the activated CH/p interaction of haloalkanes, gas phase cluster studies have been scarce. [19][20][21][22] Zwier and coworkers reported the electronic transitions of benzene-CHCl 3 and they deduced the nature of the on-top p-hydrogen-bonded structure, where the C-H bond is along the the six-fold axis of benzene, on the basis of the vibronic structure of the electronic spectra. 20 They also observed the electronic transition of benzene-CH 3 Cl.…”

“…[19][20][21][22] Zwier and coworkers reported the electronic transitions of benzene-CHCl 3 and they deduced the nature of the on-top p-hydrogen-bonded structure, where the C-H bond is along the the six-fold axis of benzene, on the basis of the vibronic structure of the electronic spectra. 20 They also observed the electronic transition of benzene-CH 3 Cl. 19 The blue-shift of the S 1 -S 0 electronic transition upon cluster formation increases with the progress of the chlorine-substitution.…”