Polycationic Ru(II) Luminophores: Syntheses, Photophysics, and Application in Electrostatically Driven Sensitization of Lanthanide Luminescence.

A series of photoluminescent Ru(II) polypyridine complexes have been synthesized in a manner that varies the extent of the cationic charge. Two ligand systems (L1 and L2), based upon 2,2'-bipyridine (bipy) mono- or difunctionalized at the 5- or 5,5'-positions using N-methylimidazolium groups, were utilized. The resulting Ru(II) species therefore carried +3, +4, +6, and +8 complex moieties based on a [Ru(bipy)3]2+ core. Tetra-cationic [Ru(bipy)2(L2)][PF6]4 was characterized using XRD, revealing H-bonding interactions between two of the counteranions and the cationic unit. The ground-state features of the complexes were found to closely resemble those of the parent unfunctionalized [Ru(bipy)3]2+ complex. In contrast, the excited state properties produce a variation in emission maxima, including a bathochromic 44 nm shift of the 3MLCT band for the tetra-cationic complex; interestingly, further increases in overall charge to +6 and +8 produced a hypsochromic shift in the 3MLCT band. Supporting DFT calculations suggest that the trend in emission behavior may, in part, be due to the precise nature of the LUMO and its localization. The utility of a photoactive polycationic Ru(II) complex was then demonstrated through the sensitization of a polyanionic Yb(III) complex in free solution. The study shows that electrostatically driven ion pairing is sufficient to facilitate energy transfer between the 3MLCT donor state of the Ru(II) complex and the accepting 2F5/2 excited state of Yb(III).

Polysubstituted Ligand Framework for Color Tuning Phosphorescent Iridium(III) Complexes.

A series of ligands have been synthesized based upon a polysubstituted 2-phenylquinoxaline core structure. These ligands introduce different combinations of fluorine and methyl substituents on both the phenyl and quinoxaline constituent rings. The resultant investigation of these species as cyclometalating agents for Ir(III) gave cationic complexes of the form [Ir(C^N)2(bipy)]PF6 (where C^N = cyclometalating ligand; bipy = 2,2'-bipyridine). X-ray crystallographic studies were conducted on four complexes and each revealed the expected distorted octahedral geometry based upon a cis-C,C and trans-N,N ligand arrangement at Ir(III). Supporting computational studies predict that each of the complexes share the same general descriptions for the frontier orbitals. TD-DFT calculations suggest MLCT contributions to the lowest energy absorption and a likely MLCT/ILCT/LLCT nature to the emitting state. Experimentally, the complexes display tunable luminescence across the yellow-orange-red part of the visible spectrum (λem = 579-655 nm).

Bis-cyclometalated iridium(iii) complexes with terpyridine analogues: syntheses, structures, spectroscopy and computational studies.

Two ligands based upon a 2,6-disubstituted pyridine bridge introduce bis-quinoxalinyl units in a fashion that yields analogues to the archetypal terdentate ligand, 2,2':6',2''-terpyridine. The ligands were synthesised from the key intermediate 2,6-bis(bromoacetyl)pyridine: a new, high-yielding route is described for this reagent. Two ligand variants (differentiated by H/Me substituents on the quinoxaline ring) were explored as coordinating moieties for iridium(iii) in the development of luminescent complexes. Computational studies (DFT approaches employing B3LYP, B3LYP/LANL2DZ, and M062X/LANL2DZ levels) were used to investigate the geometric and coordination mode preferences of the new ligands and two possibilities arose from theoretical investigations: [Ir(N^N^N)2]3+ and [Ir(N^N^C)2]+, with the former predicted to be more energetically favourable. Upon synthesis and isolation of the Ir(iii) complexes, X-ray crystallographic studies revealed coordination spheres that were cyclometalated, the structures both showing a [Ir(N^N^C)2]PF6 arrangement. Further spectroscopic characterization via NMR confirmed the ligand arrangements in the complexes, and photophysical studies, supported by DFT, showed that a mixture of metal-to-ligand charge transfer (MLCT) and intra-ligand charge transfer (ILCT) character is likely to contribute to the emission features of the complexes, which phosphoresce orange-red (λ em = 580-618 nm). The emission wavelength was influenced by the substituents on the quinoxaline ring (H vs. Me), thereby implying further tuneability is possible with future ligand iterations.

Iridium(III) Sensitisers and Energy Upconversion: The Influence of Ligand Structure upon TTA-UC Performance.

Six substituted ligands based upon 2-(naphthalen-1-yl)quinoline-4-carboxylate and 2-(naphthalen-2-yl)quinoline-4-carboxylate have been synthesised in two steps from a range of commercially available isatin derivatives. These species are shown to be effective cyclometallating ligands for IrIII , yielding complexes of the form [Ir(C^N)2 (bipy)]PF6 (where C^N=cyclometallating ligand; bipy=2,2'-bipyridine). X-ray crystallographic studies on three examples demonstrate that the complexes adopt a distorted octahedral geometry wherein a cis-C,C and trans-N,N coordination mode is observed. Intraligand torsional distortions are evident in all cases. The IrIII complexes display photoluminescence in the red part of the visible region (668-693 nm), which is modestly tuneable through the ligand structure. The triplet lifetimes of the complexes are clearly influenced by the precise structure of the ligand in each case. Supporting computational (DFT) studies suggest that the differences in observed triplet lifetime are likely due to differing admixtures of ligand-centred versus MLCT character instilled by the facets of the ligand structure. Triplet-triplet annihilation upconversion (TTA-UC) measurements demonstrate that the complexes based upon the 1-naphthyl derived ligands are viable photosensitisers with upconversion quantum efficiencies of 1.6-6.7 %.

Spectroscopic and Theoretical Investigation of Color Tuning in Deep-Red Luminescent Iridium(III) Complexes.

A series of heteroleptic, neutral iridium(III) complexes of the form [Ir(L)2(N^O)] (where L = cyclometalated 2,3-disubstituted quinoxaline and N^O = ancillary picolinate or pyrazinoate) are described in terms of their synthesis and spectroscopic properties, with supporting computational analyses providing additional insight into the electronic properties. The 10 [Ir(L)2(N^O)] complexes were characterized using a range of analytical techniques (including 1H, 13C, and 19F NMR and IR spectroscopies and mass spectrometry). One of the examples was structurally characterized using X-ray diffraction. The redox properties were determined using cyclic voltammetry, and the electronic properties were investigated using UV-vis, time-resolved luminescence, and transient absorption spectroscopies. The complexes are phosphorescent in the red region of the visible spectrum (λem = 633-680 nm), with lifetimes typically of hundreds of nanoseconds and quantum yields ca. 5% in aerated chloroform. A combination of spectroscopic and computational analyses suggests that the long-wavelength absorption and emission properties of these complexes are strongly characterized by a combination of spin-forbidden metal-to-ligand charge-transfer and quinoxaline-centered transitions. The emission wavelength in these complexes can thus be controlled in two ways: first, substitution of the cyclometalating quinoxaline ligand can perturb both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital levels (LUMO, Cl atoms on the ligand induce the largest bathochromic shift), and second, the choice of the ancillary ligand can influence the HOMO energy (pyrazinoate stabilizes the HOMO, inducing hypsochromic shifts).

An Extended Computational Study of Criegee Intermediate-Alcohol Reactions.

High-level ab initio calculations (DF-LCCSD(T)-F12a//B3LYP/aug-cc-pVTZ) are performed on a range of stabilized Criegee intermediate (sCI)-alcohol reactions, computing reaction coordinate energies, leading to the formation of α-alkoxyalkyl hydroperoxides (AAAHs). These potential energy surfaces are used to model bimolecular reaction kinetics over a range of temperatures. The calculations performed in this work reproduce the complicated temperature-dependent reaction rates of CH2OO and (CH3)2COO with methanol, which have previously been experimentally determined. This methodology is then extended to compute reaction rates of 22 different Criegee intermediates with methanol, including several intermediates derived from isoprene ozonolysis. In some cases, sCI-alcohol reaction rates approach those of sCI-(H2O)2. This suggests that in regions with elevated alcohol concentrations, such as urban Brazil, these reactions may generate significant quantities of AAAHs and may begin to compete with sCI reactions with other trace tropospheric pollutants such as SO2. This work also demonstrates the ability of alcohols to catalyze the 1,4-H transfer unimolecular decomposition of α-methyl substituted sCIs.

Ligand-Tuneable, Red-Emitting Iridium(III) Complexes for Efficient Triplet-Triplet Annihilation Upconversion Performance.

A series of substituted 2-phenylquinoxaline ligands have been explored to finely tune the visible emission properties of a corresponding set of cationic, cyclometallated iridium(III) complexes. The electronic and redox properties of the complexes were investigated through experimental (including time-resolved luminescence and transient absorption spectroscopy) and theoretical methods. The complexes display absorption and phosphorescent emissions in the visible region that are attributed to metal to ligand charge-transfer transitions. The different substitution patterns of the ligands induce variations in these parameters. Time-dependent DFT studies support these assignments and show that there is likely to be a strong spin-forbidden contribution to the visible absorption bands at λ=500-600 nm. Calculations also reliably predict the magnitude and trends in triplet emitting wavelengths for the series of complexes. The complexes were assessed as potential sensitisers in triplet-triplet annihilation upconversion experiments by using 9,10-diphenylanthracene as the acceptor; the methylated variants performed especially well with impressive upconversion quantum yields of up to 39.3 %.

Customizing Photoredox Properties of PXX-based Dyes through Energy Level Rigid Shifts of Frontier Molecular Orbitals.

Here we describe the synthesis of electron-rich PXX derivatives in which the energy levels of the excited states have been rigidly shifted through the insertion of imide groups. This has allowed the development of a new series of oxygen-doped photoredox-active chromophores with improved oxidizing and reducing properties. Capitalizing on the dehalogenation of organic halides as a model reaction, we could investigate the photooxidative and photoreductive potential of these molecules in model chemical transformations. Depending on the substrate, solvent and dye the reaction mechanism can follow different paths. This prompted us to consider the first chemoselective transformation protocol, in which two different C-Br bonds could be chemoselectively reacted through the sequential photoactivation of two different colorants.

Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates.

The rate coefficients for gas-phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240-340 K. The rate coefficients k(CH2 OO + CF3 COOH)=(3.4±0.3)×10-10  cm3 s-1 and k((CH3 )2 COO + CF3 COOH)=(6.1±0.2)×10-10  cm3 s-1 at 294 K exceed estimates for collision-limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre-reactive complex. Fits to a model incorporating this complex formation give k [cm3 s-1 ]=(3.8±2.6)×10-18  T2 exp((1620±180)/T) + 2.5×10-10 and k [cm3 s-1 ]=(4.9±4.1)×10-18  T2 exp((1620±230)/T) + 5.2×10-10 for the CH2 OO + CF3 COOH and (CH3 )2 COO + CF3 COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.

From Ligand to Phosphor: Rapid, Machine-Assisted Synthesis of Substituted Iridium(III) Pyrazolate Complexes with Tuneable Luminescence.

A first-generation machine-assisted approach towards the preparation of hybrid ligand/metal materials has been developed. A comparison of synthetic approaches demonstrates that incorporation of both flow chemistry and microwave heating can be successfully applied to the rapid synthesis of a range of new phenyl-1H-pyrazoles (ppz) substituted with electron-withdrawing groups (-F, -CF3 , -OCF3 , and -SF5 ). These, in turn, can be translated into heteroleptic complexes, [Ir(ppz)2 (bipy)]BF4 (bipy=2,2'-bipyridine). Microwave-assisted synthesis for the IrIII complexes allows isolation of spectroscopically pure species in less than 1 h of reaction time starting from IrCl3 . All of the new complexes have been characterised photophysically (including nanosecond time-resolved transient absorption spectroscopy), electrochemically, and by TD-DFT studies. The complexes exhibit ligand-dependent, tuneable, green-yellow luminescence (500-560 nm), with quantum yields in the range 5-15 %.

UV Photodissociation Dynamics of the CH3CHOO Criegee Intermediate: Action Spectroscopy and Velocity Map Imaging of O-Atom Products.

UV excitation of jet-cooled CH3CHOO on the B(1)A'-X(1)A' transition results in dissociation to two spin-allowed product channels: CH3CHO X(1)A' + O (1)D and CH3CHO a(3)A″ + O (3)P. The O (1)D and O (3)P products are detected using 2 + 1 REMPI at 205 and 226 nm, respectively, for action spectroscopy and velocity map imaging studies. The O (1)D action spectrum closely follows the previously reported UV absorption spectrum for jet-cooled CH3CHOO [Beames et al. J. Chem. Phys. 2013 , 138 , 244307]. Velocity map images of the O (1)D products following excitation of CH3CHOO at 305, 320, and 350 nm exhibit anisotropic angular distributions indicative of rapid (ps) dissociation, along with broad and unstructured total kinetic energy (TKER) distributions that reflect the internal energy distribution of the CH3CHO X(1)A' coproducts. The O (3)P action spectrum turns on near the peak of the UV absorption spectrum (ca. 324 nm) and extends to higher energy with steadily increasing O (3)P yield. Excitation of CH3CHOO at 305 nm, attributed to absorption of the more stable syn-conformer, also results in an anisotropic angular distribution of O (3)P products arising from rapid (ps) dissociation, but a narrower TKER distribution since less energy is available to the CH3CHO a(3)A″ + O (3)P products. The threshold for the higher energy CH3CHO a(3)A″ + O (3)P product channel is determined to be ca. 88.4 kcal mol(-1) from the termination of the TKER distribution and the onset of the O (3)P action spectrum. This threshold is combined with the singlet-triplet spacings of O atoms and acetaldehyde to establish the dissociation energy for syn-CH3HOO X(1)A' to the lowest spin-allowed product channel, CH3CHO X(1)A' + O (1)D, of ≤55.9 ± 0.4 kcal mol(-1). A harmonic normal-mode analysis is utilized to identify the vibrational modes of CH3CHO likely to be excited upon dissociation into the two product channels.

Velocity map imaging of O-atom products from UV photodissociation of the CH2OO Criegee intermediate.

UV excitation of jet-cooled CH2OO X(1)A' to the excited B(1)A' electronic states results in dissociation to two spin-allowed product channels: H2CO X(1)A1 + O (1)D and H2CO a(3)A″ + O (3)P. In this study, the higher energy H2CO a(3)A″ + O (3)P channel is characterized by velocity map imaging and UV action spectroscopy, in both cases utilizing 2 + 1 resonance enhanced multiphoton ionization detection of O (3)P products, which complements a prior experimental study on the lower energy H2CO X(1)A1 + O (1)D channel [Lehman et al., J. Chem. Phys. 139, 141103 (2013)]. Anisotropic angular distributions indicative of rapid dissociation are obtained at 330 and 350 nm, along with broad and unstructured total kinetic energy distributions that provide insight into the internal excitation of the H2CO a(3)A″ co-fragment. A harmonic normal mode analysis points to significant vibrational excitation of the CH2 wag and C-O stretch modes of the H2CO a(3)A″ fragment upon dissociation. At each UV wavelength, the termination of the kinetic energy distribution reveals the energetic threshold for the H2CO a(3)A″ + O (3)P product channel of ca. 76 kcal mol(-1) (378 nm) and also establishes the dissociation energy from CH2OO X(1)A' to H2CO X(1)A1 + O(1)D products of D0 ≤ 49.0 ± 0.3 kcal mol(-1), which is in accord with prior theoretical studies. The threshold for the H2CO a(3)A″ + O (3)P channel is also evident as a more rapid falloff on the long wavelength side of the O (3)P action spectrum as compared to the previously reported UV absorption spectrum for jet-cooled CH2OO [Beames et al., J. Am. Chem. Soc. 134, 20045 (2012)]. Modeling suggests that the O (3)P yield increases uniformly from 378 to 300 nm.

Direct production of OH radicals upon CH overtone activation of (CH3)2COO Criegee intermediates.

Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH3)2COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol(-1)) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features, indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X(2)Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH3)2COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH3CHOO and its unimolecular decay to OH products [F. Liu, J. M. Beames, A. S. Petit, A. B. McCoy, and M. I. Lester, Science 345, 1596 (2014)].

Quantum dynamical investigation of the simplest Criegee intermediate CH2OO and its O-O photodissociation channels.

The singlet electronic potential energy surfaces for the simplest Criegee intermediate CH2OO are computed over a two-dimensional reduced subspace of coordinates, and utilized to simulate the photo-initiated dynamics on the S2 (B) state leading to dissociation on multiple coupled excited electronic states. The adiabatic electronic potentials are evaluated using dynamically weighted state-averaged complete active space self-consistent field theory. Quasi-diabatic states are constructed from the adiabatic states by maximizing the charge separation between the states. The dissociation dynamics are then simulated on the diabatically coupled excited electronic states. The B ← X electronic transition with large oscillator strength was used to initiate dynamics on the S2 (B) excited singlet state. Diabatic coupling of the B state with other dissociative singlet states results in about 5% of the population evolving to the lowest spin-allowed asymptote, generating H2CO (X (1)A1) and O ((1)D) fragments. The remaining ∼95% of the population remains on repulsive B state and dissociates to H2CO (a (3)A″) and O ((3)P) products associated with a higher asymptotic limit. Due to the dissociative nature of the B state, the simulated electronic absorption spectrum is found to be broad and devoid of any vibrational structure.

Infrared-driven unimolecular reaction of CH3CHOO Criegee intermediates to OH radical products.

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the troposphere, proceeds through energized Criegee intermediates that undergo unimolecular decay to produce OH radicals. Here, we used infrared (IR) activation of cold CH3CHOO Criegee intermediates to drive hydrogen transfer from the methyl group to the terminal oxygen, followed by dissociation to OH radicals. State-selective excitation of CH3CHOO in the CH stretch overtone region combined with sensitive OH detection revealed the IR spectrum of CH3CHOO, effective barrier height for the critical hydrogen transfer step, and rapid decay dynamics to OH products. Complementary theory provides insights on the IR overtone spectrum, as well as vibrational excitations, structural changes, and energy required to move from the minimum-energy configuration of CH3CHOO to the transition state for the hydrogen transfer reaction.

UV spectroscopic characterization of dimethyl- and ethyl-substituted carbonyl oxides.

Dimethyl- and ethyl-substituted Criegee intermediates, (CH3)2COO and CH3CH2CHOO, are photolytically generated from diiodo precursors, detected by VUV photoionization at 118 nm, and spectroscopically characterized via UV-induced depletion of the m/z = 74 signals under jet-cooled conditions. In each case, UV excitation resonant with the B-X transition results in significant ground-state depletion, reflecting the large absorption cross section and rapid dynamics in the excited B state. The broad UV absorption spectra of both (CH3)2COO and CH3CH2CHOO peak at ~320 nm with absorption cross sections approaching ~4 × 10(-17) cm(2) molec(-1). The UV absorption spectra for (CH3)2COO and CH3CH2CHOO are similar to that reported previously for syn-CH3CHOO, suggesting analogous intramolecular interactions between the α-H and terminal O of the COO groups. Hydroxyl radical products generated concurrently with the Criegee intermediates are detected by 1 + 1' resonance enhanced multiphoton ionization. The OH signals, scaled relative to those for the Criegee intermediates, are compared with prior studies of OH yield from alkene ozonolysis. The stationary points along the reaction coordinates from the alkyl-substituted Criegee intermediates to vinyl hydroperoxides and OH products are also computed to provide insight on the OH yields.

Communication: Ultraviolet photodissociation dynamics of the simplest Criegee intermediate CH2OO.

The velocity and angular distributions of O (1)D photofragments arising from UV excitation of the CH2OO intermediate on the B (1)A' ← X (1)A' transition are characterized using velocity map ion imaging. The anisotropic angular distribution yields the orientation of the transition dipole moment, which reflects the π∗ ← π character of the electronic transition associated with the COO group. The total kinetic energy release distributions obtained at several photolysis wavelengths provide detail on the internal energy distribution of the formaldehyde cofragments and the dissociation energy of CH2OO X (1)A' to O (1)D + H2CO X (1)A1. A common termination of the total kinetic energy distributions, after accounting for the different excitation energies, gives an upper limit for the CH2OO X (1)A' dissociation energy of D0 ≤ 54 kcal mol(-1), which is compared with theoretical predictions including high level multi-reference ab initio calculations.

UV spectroscopic characterization of an alkyl substituted Criegee intermediate CH3CHOO.

Ozonolysis of alkenes in the troposphere proceeds through a Criegee intermediate, or carbonyl oxide, which has only recently been detected in the gas phase. The present study focuses on the production of an alkyl-substituted Criegee intermediate, CH3CHOO, in a pulsed supersonic expansion, and then utilizes VUV photoionization at 118 nm and UV-induced depletion of the m∕z = 60 signal to probe the B (1)A(') ← X (1)A(') transition. The UV-induced depletion approaches 100% near the peak of the profile at 320 nm, indicating rapid dynamics in the B state, and corresponds to a peak absorption cross section of ∼5 × 10(-17) cm(2) molecule(-1). The electronic spectrum for CH3CHOO is similar to that reported recently for CH2OO, but shifted 15 nm to shorter wavelength, which will result in a longer tropospheric lifetime for CH3CHOO with respect to solar photolysis. Complementary electronic structure calculations (EOM-CCSD) are carried out for the B and X potentials of these Criegee intermediates along the O-O coordinate. An intramolecular interaction stabilizes the ground state of the syn-conformer of CH3CHOO relative to anti-CH3CHOO, and indicates that the syn-conformer will be the more abundant species in the expansion. The excited B electronic state of syn-CH3CHOO is also predicted to be destabilized relative to that for anti-CH3CHOO and CH2OO, in accord with the shift in the B-X transition observed experimentally. Hydroxyl radicals produced concurrently with the generation of the Criegee intermediates are detected by 1+1(') resonance enhanced multiphoton ionization. The OH yield observed with CH3CHOO is 4-fold larger than that from CH2OO, consistent with prior studies of OH generation from alkene ozonolysis.

Ultraviolet spectrum and photochemistry of the simplest Criegee intermediate CH2OO.

Ozonolysis of alkenes in the troposphere produces Criegee intermediates, which have eluded detection in the gas phase until very recently. This laboratory has synthesized the simplest Criegee intermediate within a quartz capillary tube affixed to a pulsed valve to cool and isolate CH(2)OO in a supersonic expansion. UV excitation resonant with the B (1)A' ← X (1)A' transition depletes the ground-state population of CH(2)OO, which is detected by single-photon ionization at 118 nm. The large UV-induced depletion (approaching 100%) near the peak of the profile at 335 nm is indicative of rapid dissociation, consistent with the repulsive B (1)A' potential along the O-O coordinate computed theoretically. The experimental spectrum is in very good accord with the absorption spectrum calculated using the one-dimensional reflection principle. The B ← X spectrum is combined with the solar actinic flux to estimate an atmospheric lifetime for CH(2)OO at midday on the order of ∼1 s with respect to photodissociation.

Insights on the CN B 2Σ+ + Ar potential from ultraviolet fluorescence excitation and infrared depletion studies of the CN-Ar complex.

UV laser-induced fluorescence and IR-UV fluorescence depletion studies have been used to characterize the intermolecular levels of the CN-Ar complex in the excited state correlating with CN B (2)Σ(+) + Ar. Additional CN-Ar features are identified to lower wavenumber than reported previously. Fluorescence depletion spectra are recorded to confirm that these CN-Ar features and other higher energy features in the B-X spectrum originate from a common ground state level. The UV depletion is induced by IR excitation of CN-Ar from the ground state zero-point level to a hindered internal rotor state (n(K) = 1(1)) in the CN overtone region. The lowest energy feature in the B-X spectrum at 25,714.1 cm(-1) is assigned as a transition to the zero-point level of the B state and also yields its binding energy, D(0) = 186(2) cm(-1), which is in excellent accord with theoretical predictions. The next feature approximately 40 cm(-1) higher is attributed to overlapping transitions to intermolecular levels with bend (v(b)(K)=1(1)) or stretch (v(s) = 1) excitation. Yet higher features (previously reported) are also assigned, based on their transition type and wavenumber, which are consistent with the intermolecular energy level pattern computed theoretically. Finally, the intensity profile of the lowest energy features in the B-X spectrum reflects the predicted change in the CN (B (2)Σ(+), X (2)Σ(+)) + Ar potentials upon electronic excitation from a weakly anisotropic potential about the linear N≡C-Ar configuration in the ground state to a more strongly bound linear C≡N-Ar structure in the excited B electronic state.