Multi-spectroscopic and theoretical analyses on the diphenyl ether–tert-butyl alcohol complex in the electronic ground and electronically excited state

Abstract

a Aromatic ethers such as diphenyl ether (DPE) represent molecules with different docking sites for alcohols leading to competing OH-O and OH-p interactions. In a multi-spectroscopic approach in combination with quantum chemical calculations the complex of DPE with tert-butyl alcohol (t-BuOH) is investigated in the electronic ground state (S 0 ) and the electronically excited state (S 1 ). FTIR, microwave as well as mass-and isomer-selective IR/R2PI spectra are recorded, revealing co-existing OH-O and OH-p isomers in the S 0 state. Surprisingly, they are predicted to be of almost equal stability in contrast to the previously investigated DPE-MeOH complex, where the OH-p structure is preferred by both theory and experiment. The tert-butyl group in t-BuOH allows for a simultaneous optimization of hydrogen-bonding and dispersion interactions, which provides a sensitive meeting point between theory and experiment. In the electronically excited state of DPE-t-BuOH, vibrational spectra could be recorded separately for both isomers using UV/IR/UV spectroscopy. In the S 1 state the same structural binding motifs are obtained as in the S 0 state with the OH-O bond being weakened for the OH-O arrangement and the OH-p interaction being strengthened in the case of the OH-p isomer compared to the S 0 state.

The reduced cohesion of homoconfigurational 1,2-diols

“…The present work was enabled by improved nozzle designs for supersonic jet FTIR spectroscopy which remove some of the sensitivity limitations of previous designs. 73,74 By introducing wedge-shaped slit nozzles adapted to the focussed beam profile and by liquid injection into a premixing chamber, this technological limitation was significantly attenuated. The synergy with spontaneous Raman scattering tools using heatable nozzles 40 was thus enhanced.…”

The Structure of Diphenyl Ether–Methanol in the Electronically Excited and Ionic Ground States: A Combined IR/UV Spectroscopic and Theoretical Study

“…Herein, we present the resultso ft he structurali nvestigation of the DPE-MeOH complex both in electronic excited states (S 1 ,S 2 )o ft he neutral species and the cationic D 0 state by using quantum-chemical calculations and combined IR/UV spectroscopy.T he DPE alcohols ystems are known to be strongly influenced by dispersion energy in the electronic ground state. [7,13] Here, the dispersion energy of the excited state was extracted by using the (linear-response) CCS and spin-component-scaled CC2 (SCS-CC2) methods. Furthermore, ad etailed analysiso f the structure and energetics of the ionic ground state is given relative to the neutral species.…”

The Effect of Dispersion on the Structure of Diphenyl Ether Aggregates

“…Theexperiments were performed under the cold and isolated gas-phase conditions of amolecular jet, so that we were solely probing the respective aggregates,f ree from solvent effects. Theinvestigations of DPE with methanol (MeOH) [3] and tertbutanol (tBuOH) [4] revealed an unexpected behavior. In both cases,h ydrogen bonding (either to the ether oxygen or the phenyl ring) is the primary interaction, with dispersion as as econdary interaction with am ajor influence on the preferred geometries.B ecause of the different strength of dispersion interactions of the methyl group with the DPE phenyl ring, the isomer with MeOH binding to the phenyl ring (OH-p)ismore stable than the isomer with ahydrogen bond towards the ether oxygen (OH-O).…”

“…[1] As apart of van der Waals interactions,they appear as attractive forces between non-polar molecules or molecular parts.S ystematic studies of the influence of molecular interactions on structural preferences are of fundamental interest since they offer valuable insight beyond the stand-alone investigation of single systems.They reveal occasionally surprising systematic trends.T hese trends can be transferred to predict the structural properties of larger molecular systems,w hich, due to their size,c annot always be described in detail by the available experimental and theoretical methods.O ne established approach is to systematically change the size of substituents in am olecular system. Theinvestigations of DPE with methanol (MeOH) [3] and tertbutanol (tBuOH) [4] revealed an unexpected behavior. An example of asystematic analysis is the stability of am olecule depending on the size of the alkyl substituents,w hich has been studied based on the dimerization behavior of the Gomberg radical, for example.…”

“…In summary,w ep resent experimental evidence and characterization of the OH-O and OH-p isomers of DPE-H 2 O, which shows aclear preference for the OH-p isomer,by applying IR/UV and microwave spectroscopy in molecular beam experiments.I nt he case of DPE-AdOH, the OH-O complex was identified using microwave spectroscopy.W e used these experiments together with the results for DPE-MeOH [3] and DPE-tBuOH [4] complexes in combination with av ariety of calculations to describe and explain ac ounterintuitive behavior with respect to competing structures in DPE-alcohol clusters with increasing side-chain size.T hese effects are driven by dispersion energies,w hich become stronger for larger side chains.O ur systematic series points out and quantifies the importance of different competing interaction energies,aphenomenon relevant in almost all areas of chemistry.…”