Stepwise Solvation of the Intramolecular-Charge-Transfer Molecule p-(Dimethylamino)benzonitrile

Abstract

This paper presents a systematic study of gas-phase p-(7V,7V-dimethylamino)benzonitrile (DMABN) both in a supersonic jet expansion and in a thermalized vapor. From the jet studies, the excitedand ground-state vibrational spectra of the isolated molecule are resolved, and the spectroscopy of the stoichiometric complex with water, methanol, ammonia, and acetonitrile in the beam is reported. It is concluded that 1:1 complexes are not sufficient for the local perturbation to cause charge separation. At higher temperatures in the jet, we observe emission that we attribute to DMABN self-complexes. Under high pressure and temperature vapor conditions (>30 mTorr, 60 °C), red-shifted fluorescence from DMABN is observed. This is attributed to the charge-transfer state of DMABN in self-complexes.* Recipient of an Earl C. Anthony Fellowship.Contribution No. 7562. exists for a given charge-transfer or proton-transfer process. It is conceivable in the case of DMABN that a 1:1 DMABN/solvent complex could provide sufficient stabilization by charge-transfer or dipolar interactions to permit the photoisomerization of DMABN to its twisted charge-transfer state.27"30

Ground and excited state dipole moments of planar vs. twisted p-N,N-(dimethylamino)benzonitrile systems: maximum charge transfer for minimum overlap

“…Since the solvent system remains the same, it can be concluded that it is the torsional angle which directly influences Ap,. This observation is in agreement with the gas phase measurements, which clearly indicate that CT in the excited state is linked to the twisting of the phenyl-dimethylamino bond (6,7).…”

“…The fact that solvent plays a direct role comes from the following experiments. Experimental studies on DMABN in a supersonic jet expansion show that isolated molecules show only F, fluorescence and hence do not undergo twisting (6). Further evidence from spectroscopic and picosecond studies indicates that a short-range coupling interaction between a specific number of solvent molecules and the solute, either in the ground or exited state, is essential for TICT formation (4e.…”

“…For ex- 'Author to whom correspondence may be addressed at the Department of Chemistry, University of Saskatchewan, Saskatoon, Sask., Canada S7N OW0 ample, it has been proposed that local coupling of solvent molecules, with a particular local configuration, and the reactant (DMABN) is essential for the twisting of the C-NMe, bond (4e, 5 ) . This is very clear from the fact that isolated DMABN molecules in the gas phase do not emit from the TICT state even when they are allowed to complex with a specific number of solvent molecules (6). On the other hand, the fact that 2,6-N,N-(tetramethy1amino)benzonitrile (TMABN), which has the -NMe, group already twisted in the ground state, shows distinct TICT emission in the gas phase proves beyond reasonable doubt that internal twisting of the C-NMe, bond is the sole reason behind TICT emission (7).…”

Triple Emission from p‐Dimethylaminobenzonitrile–Cucurbit[8]uril Triggers the Elusive Excimer Emission

“…[2][3][4][5][6][7][8] The fundamental issues associated with the dual fluorescence of DMABN relate to the reaction pathway that connects the two states [1,2,4,7,[9][10][11][12] and the geometrical structure of the emitting ICT state. [22] We have now employed cucurbit[n]urils (CBn, n = 5-8, Scheme 1) as water-soluble macrocyclic host molecules, which are unique due to their high symmetry, rigidity, chemical inertness, and exceptional binding strengths. Experimental investigations involving differently substituted or structurally confined derivatives of DMABN, [13] as well as in media of different polarity and viscosity, [8,9,17] including the gas phase, [10] micelles, [18] solvent clusters, and supramolecular host cavities, [19][20][21] have invariably afforded evidence for the well-known dual emission, with the LE band centered around 350 nm and the ICT band around 450-500 nm.…”

Dynamics of clusters: From elementary to biological structures

“…Both electron (25)(26)(27)(28) and proton transfer (20)(21)(22)29) processes were also studied, elucidating for the former one of the classics for Mulliken's dative bonded complexes, that of benzene-iodine, and for the latter the dynamics of single and double proton transfer. With mass selection, we investigated ionic clusters, the premier being solvated electrons (30) and dioxygen anions (31)(32)(33); both are important in biological activities.…”