Rotational transitions and diffraction in D2 scattering from the LiF(001) surface: theory and experiment

High probabilities of energy transfer from translation to molecular rotations are observed in the scattering of n-D(2) from LiF(001) at an incident beam energy of 85.3 meV. For the 100 incidence direction, close-coupling calculations yield ratios of the rotationally inelastic (j=0-->2) and (j=1-->3) peaks to the rotationally elastic specular peaks (G=0) that are in reasonable agreement with experiment, as are the ratios of the rotationally elastic diffraction peak intensities to the specular peak intensities. The agreement between theory and experiment is also quite good for the rotationally inelastic diffractive (-1-1) transitions for (j=1-->3), but rather poor for (j=0-->2). The calculations show that the interaction between the electrostatic field of the surface ions and the quadrupole moment of the D(2) molecule efficiently promotes the (j=0-->2) and (j=1-->3) transitions. If this electrostatic interaction is excluded from the potential model, the ratios of the (j=0-->2) and (j=1-->3) rotationally inelastic peaks to the corresponding specular peaks show a large discrepancy with experiment, underlining the importance of this interaction. The close-coupling calculations show a somewhat worse agreement with experiment for the 110 incidence direction. In particular, the sharp peaks observed experimentally in the ratios of the peak intensities of the rotationally inelastic G=0 (j=0-->2) and (j=1-->3) to the rotationally elastic G=0 transitions as a function of incident angle are not reproduced by the calculations. The theoretical ratios of the peak intensities of the rotationally elastic diffraction to G=0 transitions are shifted to lower incidence angles with respect to experiment. The rotationally inelastic diffractive (-10) transitions present an interesting resonance phenomenon for the (j=0-->2) rotational transition. This resonance is predicted by both theory and experiment, although at rather different incident angles.     

High-resolution elastic and rotationally inelastic diffraction of D2 from NiAl(110)

High-resolution angular distributions of D(2) scattered from NiAl(110) have been measured at incident energies between 20 and 150 meV. The measurements were performed along the [110] azimuth using a high sensitivity time-of-flight apparatus, which allows the recording of diffraction channels not previously studied, including out-of-plane rotationally inelastic diffraction peaks. The attenuation of both elastic and rotationally inelastic diffraction intensities with surface temperature was found to follow a Debye-Waller model. The time-of-flight data analysis allowed us to assign unequivocally the different transition probabilities to each final state. In this way, 0→2, 2→0, and 1→3 transition probabilities were observed, covering relative intensities over two orders of magnitude. In the energy range investigated, the 0→2 transition was found to be a factor of 2-3 larger than the 2→0 one, which lies a factor of 10 above the 1→3 transition probability.     

Optics of light scattering caused by liquid-crystal-director fluctuations

We have applied the light-scattering equation caused by liquid-crystal (LC)-director fluctuations as derived by De Gennes [1] to the case where the polarization direction of the incident light is at an arbitrary angle with respect to the LC directors within the cell. Based on the De Gennes’s equation, we have used an out-of-plane (OPR) cell-rotation method to measure the pretilt angles of a tilted-homogeneously aligned LC cell. Our measured pretilt angles are in good agreement with that obtained by the published OPR-rotation method [2] based on a different mechanism. Our method is simple in setup and requires no complicated data-fitting calculations when the pretilt angles are below about 30°. In addition, there is no need to know cell parameters except the ordinary and extraordinary refractive indices of the LC medium at the wavelength of incident light.     

The complex coordinate scattering theroy and its application to the study of the surface asymmetry effect in helium diffraction from copper

The Complex Coordinate Scattering Theory is reformulated for the general case of a time-independent Hamiltonian. It is applied to scattering of He atoms from a Cu(115) crystal surface by constracting the Green operator for the T-matrix from the eigenvectors of both the complex scaled Hamiltonian and its transposed (“right” and “left” eigenvectors), which are different in this case. The weakly asymmetric corrugation function describing the (115) face of Cu is shown to cause a strong dependence of the calculated diffraction intensities upon the direction of the incident atomic beam. The calculated transition probabilities are in excellent agreement with the experimentally measured ones, previously obtained by Perreau and Lapujoulade. We show that additional information about the gas atom/surface physisorption interaction potential can be obtained if the incident angle of the atomic beam (the angles between the beam and the surface normal) is changed from γ to ?γ. © 1993 John Wiley & Sons, Inc.     

Correlated angular and quantum state-resolved CO2 scattering dynamics at the gas-liquid interface

Molecular beam scattering dynamics at the gas-liquid interface are investigated for CO2 (E(inc) = 10.6(8) kcal/mol) impinging on liquid perfluoropolyether (PFPE), with quantum state (v, J) populations measured as a function of incident (theta(inc)) and final (theta(scat)) scattering angles. The internal state distributions are well-characterized for both normal and grazing incident angles by a two-component Boltzmann model for trapping desorption (TD) and impulsive scattering (IS) at rotational temperatures T(rot)(TD/IS), where the fractional TD probability for CO2 on the perfluorinated surface is denoted by TD and IS densities (rho) as alpha = rhoTD/(rhoTD + rhoIS). On the basis of an assumed cos(theta(scat)) scattering behavior for the TD flux component, the angular dependence of the IS flux at normal incidence (theta(inc) = 0 degrees) is surprisingly well-modeled by a simple cos(n)(theta(scat)) distribution with n = 1.0 +/- 0.2, while glancing incident angles (theta(inc) = 30 degrees, 45 degrees, and 60 degrees) result in lobular angular IS distributions scattered preferentially in the forward direction. This trend is also corroborated in the TD fraction alpha, which decreases rapidly under non-normal incident conditions as a function of backward versus forward scattering direction. Furthermore, the extent of rotational excitation in the IS channel increases dramatically with increasing angle of incidence, consistent with an increasing rotational torque due to surface roughness at the gas-liquid interface.     

Systematic studies of early actinide complexes: uranium(IV) fluoroketimides

The reaction of (C5Me5)2U(CH3)2 with 2 equiv of N[triple bond]C-ArF gives the fluorinated uranium(IV) bis(ketimide) complexes (C5Me5)2U[-N=C(CH3)(ArF)]2 [where ArF=2-F-C6H4 (4), 3-F-C6H4 (5), 4-F-C6H4 (6), 2,6-F2-C6H3 (7), 3,5-F2-C6H3 (8), 2,4,6-F3-C6H2 (9), 3,4,5-F3-C6H2 (10), and C6F5 (11)]. These have been characterized by single-crystal X-ray diffraction, 1H and 19F NMR, cyclic voltammetry, UV-visible-near-IR absorption spectroscopy, and variable-temperature magnetic susceptibility. Density functional theory (DFT) results are reported for complexes 6 and 11 for comparison with experimental data. The most significant structural perturbation imparted by the F substitution in these complexes is a rotation of the fluorinated aryl (ArF) group out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 7, 9, and 11 when the ArF group possesses two o-fluorine atoms. Excellent agreement is obtained between the DFT-calculated and experimental crystal structures for 11, which displays the distortion, as well as for 6, which does not. In 7, 9, and 11, the out-of-plane rotation results in large angles (phi=53.7-89.4 degrees) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups. Complexes 6 and 10 do not contain o-fluorine atoms and display interplanar angles in the range of phi=7-26.8 degrees. Complex 4 with a single o-fluorine substituent has intermediate values of phi=20.4 and 49.5 degrees. The distortions in 7, 9, and 11 result from an unfavorable steric interaction between one of the two o-fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. All complexes exhibit UV/UIV and UIV/UIII redox couples, although the distortion in 7, 9, and 11 appears to be a factor in rendering the UIV/UIII couple irreversible. The potential separation between these couples remains constant at 2.15+/-0.03 V. The electronic spectra are dominated by unusually intense f-f transitions in the near-IR that retain nearly identical band energies but vary in intensity as a function of the fluorinated ketimide ligand, and visible and near-UV bands assigned to metal (5f)-to-ligand (pi*) charge-transfer and interconfiguration (5f2-->5f16d1) transitions, respectively. Variable-temperature magnetic susceptibility data for these complexes indicate a temperature-independent paramagnetism (TIP) below approximately 50 K that results from admixing of low-lying crystal-field excited states derived from the symmetry-split 3H4 5f2 manifold into the ground state. The magnitude of the TIP is smaller for the complexes possessing two o-fluorine atoms (7, 9, and 11), indicating that the energy separation between ground and TIP-admixed excited states is larger as a consequence of the greater basicity of these ligands.     

Water line lists close to experimental accuracy using a spectroscopically determined potential energy surface for H2(16)O, H2(17)O, and H2(18)O

Line lists of vibration-rotation transitions for the H(2) (16)O, H(2) (17)O, and H(2) (18)O isotopologues of the water molecule are calculated, which cover the frequency region of 0-20 000 cm(-1) and with rotational states up to J=20 (J=30 for H(2) (16)O). These variational calculations are based on a new semitheoretical potential energy surface obtained by morphing a high accuracy ab initio potential using experimental energy levels. This potential reproduces the energy levels with J=0, 2, and 5 used in the fit with a standard deviation of 0.025 cm(-1). Linestrengths are obtained using an ab initio dipole moment surface. That these line lists make an excellent starting point for spectroscopic modeling and analysis of rotation-vibration spectra is demonstrated by comparison with recent measurements of Lisak and Hodges [J. Mol. Spectrosc. (unpublished)]: assignments are given for the seven unassigned transitions and the intensity of the strong lines are reproduced to with 3%. It is suggested that the present procedure may be a better route to reliable line intensities than laboratory measurements.     

Crystal and molecular structure of an eight-coodinate N-methyltetraphenylporphyrin complex: diacetato(N-methyl-meso-tetraphenylporphyrinato)thallium(III)

The crystal structure of diacetato(N-methyl-meso-tetraphenylporphyrinato)thallium(III), Tl(N-Me-tpp)(OAc)2 (1), was established, and the coordination sphere around the Tl3+ ion is described as an eight-coordinate square-based antiprism in which two cis chelating bidentate OAc- groups occupy two apical sites. The plane of the three pyrrole nitrogen atoms (i.e., N(1), N(3), N(4)) strongly bonded to Tl3+ is adopted as a reference plane 3N. The pyrrole N(2) ring bearing the methyl group (i.e., C(45)H3) is the most deviated one from the 3N plane, making a dihedral angle of 21.4 degrees, whereas smaller angles of 9.1 degrees, 7.1 degrees, and 0.9 degree occur with pyrroles N(1), N(3), and N(4), respectively. Because of its larger size, the thallium(III) ion Tl3+ is considerably out of the 3N plane; its displacement of 1.17 A is in the same direction as that of the two apical OAc- ligands. The intermolecular acetate exchange process for 1 in THF-d8 solvent is examined through 1H NMR temperature-dependent measurements. In the slow-exchange region, the methyl and carbonyl carbons of the OAc- groups in 1 are separately located at delta 18.6 [3J(Tl-13C) = 405 Hz] and 170.8 [2J(Tl-13C) = 334 Hz] at -80 degrees C, respectively.     

Experimental and theoretical study of rotationally inelastic diffraction of D2 from NiAl(110)

We present a detailed experimental and theoretical study of elastic and rotationally inelastic diffraction of D(2) from NiAl(110) in the energy range 85-150 meV. The experiments were performed using a high-resolution, fixed angle geometry apparatus. Quantum and classical dynamical calculations were performed by using a six-dimensional potential energy surface constructed upon interpolation of a set of DFT (density functional theory) data. We show that, although elastic diffraction peak intensities are accurately described by theory in the whole range of incidence energies and angles explored, significant discrepancies are obtained for RID peaks, especially for those involving rotational initial states with j(i) > 0. Possible reasons for this discrepancy are discussed.     

Rainbows and glories in the angular scattering of the state-to-state F + H2 reaction at E(trans)=0.04088 eV

State-of-the-art differential cross sections (DCSs) have been reported by Wang et al. [Proc. Nat. Acad. Sci. (U.S.), 2008, 105, 6227] for the state-to-state F + H(2)→ FH + H reaction using fully quantum-state-selected crossed molecular beams. We theoretically analyze the angular scattering of this reaction, in order to quantitatively understand the physical content of structure in the DCSs. Three transitions are studied, v(i)=0, j(i)=0, m(i)=0 → v(f)=3, j(f)=0, 1, 2, m(f)=0 at a translational energy of 0.04088 eV, where v, j, m are the vibrational, rotational and helicity quantum numbers respectively for the initial and final states. The input to our analyses consists of accurate quantum scattering (S) matrix elements computed for the Fu-Xu-Zhang potential energy surface, as used by Wang et al. in a computational simulation of their experimental DCSs. We prove that the pronounced peak at forward angles observed in the experimental and simulated DCSs for all three transitions is a glory. At larger angles, it is demonstrated that the 000 → 300 and 000 → 310 DCSs both possess a broad farside rainbow, which is accompanied by diffraction oscillations. We confirm the conjecture of Wang et al. that these diffraction oscillations arise from nearside-farside (NF) interference. We find that the reaction is N dominant for all three transitions. The theoretical techniques used to analyze the angular scattering include uniform semiclassical theories of glory and of rainbow scattering. We also make the first application of a semiclassical formula that is uniform for both glory + rainbow scattering. In addition, structure in the DCSs is analyzed using NF theory and local angular momentum theory, in both cases with three resummations of the partial wave series for the scattering amplitude. We make the first explicit application of the Thiele rational interpolation formula to extract the position and residue of the leading Regge pole from a set of S matrix elements, thereby making contact with complex angular momentum theories of DCSs, which interpret the angular scattering in terms of Regge resonances. Our calculations complement the exit-valley vibrationally-adiabatic analysis of Wang et al.     

Time-dependent wavepacket calculations of atom scattering from surfaces with impurities

Exact quantum-mechanical calculations are reported on atom scattering from a crystalline surface with isolated impurities. The calculations are for He scattering from a one-dimensional model of a Cu surface with adsorbed Ar atoms. The difficulties of carrying out calculations on scattering from extended but non-periodic structures are overcome by using a time-dependent wavepacket approach. A recently developed method for solving the time-dependent Schrödinger equation is employed. Scattering intensities are given for several energies and incidence angles. Detailed insight is obtained on impurity effects on surface scattering. The main features are: (1) Broad intensity tails are superimposed on each diffraction spike. The width of the tails decreases with increasing diffraction order; (2) Shallow rainbow peaks arise, due to impurity induced local corrugation; (3) Weak intensity maxima arise due to interference between surface and impurity scattering. The intensities are somewhat sensitive to the position of the impurity within the surface unit cell. Physical interpretation of the effects is provided from exact calculations, and from a simple sudden approximation for the scattering intensities. It is argued that He scattering can be used to determine impurity locations on surfaces.     

S 1←S 0 vibronic spectra and inversion potentials in theS 1 states of acetyl and formyl halides

The potential functions of inversion in the S₁ states are determined from the inversion transitions (out-of-plane C=O vibrations) found in the S₁←S₀ vibronic spectra of acetyl halide molecules. The high intensities of the hot inversion transitions are explained by the high probabilities of these transitions. The literature values of the inversion potentials (equilibrium values of angles formed by the C=O bonds deviating from the planes) of formyl halide molecules in the S₁ states are refined. The inversion potentials of formyl and acetyl halides are similar. M. V. Lomonosov Moscow State University, Chemical Faculty. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 316–321, March–April, 1995. Translated by L. Smolina     

Crystal structure of friction-transferred poly(2,5-dioctyloxy-1,4-phenylenevinylene)

Poly(2,5-dioctyloxy-1,4-phenylenevinylene) (DOPPV) was found to form a highly oriented film by a friction-transfer technique. Structural investigation of friction-transferred DOPPV was studied by means of polarized ultraviolet-visible (UV-vis) absorption spectroscopy, polarized photoluminescence (PL) spectroscopy, and synchrotron-sourced grazing incident X-ray diffraction (GIXD) analysis. The polarized UV-vis absorption and PL spectra indicate clear axial alignment. DOPPV backbones in friction-transferred film are highly aligned along the drawing direction of the friction-transfer. Further information of the molecular arrangement in friction-transferred DOPPV film was investigated by both the out-of-plane and the in-plane GIXD analyses with synchrotron source. The DOPPV molecules in friction-transferred films were perfectly arranged three-dimensionally: the backbones aligned along the drawing direction of friction-transfer, the alkyl side chains lay in the film plane, and the planar backbones were arranged parallel to the film surface. Additionally, two neighboring DOPPV molecules along the direction of inter-backbones separation by alkyl side chains were found to be shifted with respect to one another by the mean distance of half of a monomeric repeat.     

[(C_(16)H_(32)N_4)~(-4)·2Mn~(2+)·4HCl·[(C_(16)H_(36)N_4)·2H_2O]多元包合物的晶体结构

[(4氮间杂六甲基十四烷环)~(-4)·2Mn~(2+)]·4HCl·[4氮间杂六甲基十四烷环)·2H_2O]的晶体结构已用单晶X线衍射技术测定完成。它属于三斜晶系,P_1空间群,晶胞参数a=9.028(2),b=11.055(2),c=12.202(4),α=71.70(2),B=88.41(2),γ=75.32(2)~°,Z=1。对于2597个可观察独立反射计算R=0.073。结构分析证实,该晶体存在有四类物种,由负4价的四氮间杂六甲基十四烷环(简称电负性大环Ⅱ),2个Mn~(2+)正离子,4个HCl分子和一个携带2个结晶水的4氮间杂六甲基十四烷环(简称电中性大环Ⅰ)组成。 4个HCl分子处于电负性大环Ⅱ的周围,大环Ⅱ和Mn~(2+)离子间按离子键特点取空间最稳定构型与电中性大环Ⅰ沿c方向周期性交替排布,构成四元包合物O~-、N~-、Cl~-等电负性强的离子之间形成很强的H键网。 六十年代以来,以四氨间杂六甲基十四烷环作配体,以Co~(2+)、Co~(3+)、Ni~(2+)等金属离子为络合中心的大环络合物,国外已有许多报导。这些结构的共同特点是大环配体的4个氮原子围绕金属离子以构成四配位或六配位结构,研究表明,络合以后金属的电子组态发生了变化。 近来,我们将Mn~(2+)与上述的配体反应,结果得到与上述结构绝然不同的化合物。NMR谱证实,该化合物中包含电中性和电负性两种大环。环伏安法测其锰离子是2价正离子(详见     

Electronic spectral studies of molybdenyl complexes. 2. MCD spectroscopy of [MoOS4]- centers

Magnetic circular dichroism (MCD) and absorption spectroscopies have been used to probe the electronic structure of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] complexes (edt = ethane-1,2-dithiolate). The results of density functional calculations (DFT) on [MoO(SMe)4]- and [MoO(edt)2]- model complexes were used to provide a framework for the interpretation of the spectra. Our analysis shows that the lowest energy transitions in [MoVOS4] chromophores (S4 = sulfur donor ligand) result from S-->Mo charge transfer transitions from S valence orbitals that lie close to the ligand field manifold. The energies of these transitions are strongly dependent on the orientation of the S lone-pair orbitals with respect to the Mo atom that is determined by the geometry of the ligand backbone. Thus, the lowest energy transition in the MCD spectrum of [PPh4][MoO(p-SC6H4X)4] (X = H) occurs at 14,800 cm-1, while that in [PPh4][MoO(edt)2] occurs at 11,900 cm-1. The identification of three bands in the absorption spectrum of [PPh4][MoO(edt)2] arising from LMCT from S pseudo-sigma combinations to the singly occupied Mo 4d orbital in the xy plane suggests that there is considerable covalency in the ground-state electronic structures of [MoOS4] complexes. DFT calculations on [MoO(SMe)4]- reveal that the singly occupied HOMO is 53% Mo 4dxy and 35% S p for the equilibrium C4 geometry. For [MoO(edt)2]- the steric constraints imposed by the edt ligands result in the S pi orbitals being of similar energy to the Mo 4d manifold. Significant S pseudo-sigma and pi donation may also weaken the Mo identical to O bond in [MoOS4] centers, a requirement for facile active site regeneration in the catalytic cycle of the DMSO reductases. The strong dependence of the energies of the bands in the absorption and MCD spectra of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] on the ligand geometry suggests that the structural features of the active sites of the DMSO reductases may result in an electronic structure that is optimized for facile oxygen atom transfer.     

Observation of zinc phthalocyanine aggregates on a water surface using grazing incidence X-ray scattering

Reported here are the structural properties of a zinc 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine Langmuir monolayer on a water surface under progressive lateral compression investigated by grazing incidence X-ray scattering. Grazing incidence diffuse X-ray scattering out of the specular plane (GIXOS) is exploited to determine specular reflectivity-like information where the phase change of flat-lying molecules on the surface to edge-standing molecules perpendicular to the surface is directly observed. Furthermore, grazing incident X-ray diffraction (GIXD) is used to investigate the in-plane ordering of the system where it has been found that in the high-density state (approximately 0.35 nm2 per molecule) the system can be considered to be a monolayer consisting of arrays of side-by-side lying cofacially aggregated cylindrical rodlike entities.     

A resonance Raman,surface-enhanced resonance Raman,IR, and ab initio vibrational spectroscopic study of nickel(II) tetraazaannulene complexes

The IR and resonance Raman spectra of the nickel(II) complexes of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) and 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TMTAA) have been measured and compared with ab initio calculations of the vibrational wavenumbers at the B3-LYP level using the LanL2DZ basis set. An excellent fit is found between the experimental and calculated data, enabling precise vibrational assignments to be made. Surface-enhanced resonance Raman spectra were obtained following adsorption on Ag electrodes, with potentials in the range -0.1 to -1.1 V vs Ag/AgCl. There is evidence for contributions from both the electromagnetic and charge transfer (CT) surface enhancement mechanisms. The data indicate that variations in band intensities with electrode potential can be interpreted in terms of the CT mechanism.     

Extracting maximum information from polarized surface vibrational spectra: application to etched, H-terminated Si(110) surfaces

A general method to maximize the information extracted from polarized surface absorption spectra is developed and applied to the study of etched Si(110) surfaces. In essence, this technique transforms spectra from the experimental reference frame, which is defined by the direction of the surface electric field during irradiation by s- and p-polarized light, into a more appropriate Cartesian reference frame defined by the surface normal and the plane of incidence. If the Cartesian reference frame is aligned with high symmetry directions of the system, significant spectral simplification can result. This analysis relies on the well-known boundary conditions on interfacial electric fields and is independent of any adsorbate screening or the effective dielectric constant of the adsorbate layer. The validity of this analysis is demonstrated on the spectra of NH4F-etched, H-terminated Si(110). The transition dipole moments of the symmetric and antisymmetric Si[Single Bond]H stretch modes associated with flat terraces are polarized along the [110] and [001] directions, respectively. Two additional modes with transition dipoles polarized along the [001] and [110] directions are assigned to defect species associated with microfaceting and other surface roughness. Data taken in two different experimental geometries are shown to be in excellent quantitative agreement, confirming the validity of the technique. Additionally, the measured adsorbate layer dielectric constant is in good agreement with previously reported values for hydrogen-terminated silicon surfaces.     

Diazaborolyl-boryl push-pull systems with ethynylene-arylene bridges as 'turn-on' fluoride sensors

Two linear π-conjugated systems with 1,3-diethyl-1,3,2-benzodiazaborolyl [C(6)H(4)(NEt)(2)B-] as a donor group and dimesitylboryl (-BMes(2)) as acceptor were synthesised with -ethynylene-phenylene- (-C[triple bond, length as m-dash]C-1,4-C(6)H(4)-, 3) and -ethynylene-thiophene- (-C[triple bond, length as m-dash]C-2,5-C(4)H(2)S-12) bridges between the boron atoms. An assembly (20) consisting of two diazaborolyl-ethynylene-phenylene-boryl units, [C(6)H(4)(NCy)(N')B-C[triple bond, length as m-dash]C-1,4-C(6)H(4)-BMes(2)] joined via a 1,4-phenylene unit at the nitrogen atoms (N') of the diazaborolyl units was also synthesised. The three push-pull systems, 3, 12 and 20, form salts on fluoride addition with the BMes(2) groups converted into (BMes(2)F)(-) anions. The molecular structures of 3, 12 and (NBu(4))(12·F) were elucidated by X-ray diffraction analyses. The borylated systems 3, 12 and 20 show intense blue luminescence in cyclohexane with quantum yields (Φ(fl)) of 0.99, 0.44 and 0.94, respectively, but weak blue-green luminescence in tetrahydrofuran (Φ(fl) = 0.02-0.05). The charge transfer nature of these transitions is supported by TD-DFT computations with the CAM-B3LYP functional. Addition of tetrabutylammonium fluoride to tetrahydrofuran solutions of 3 and 20 resulted in strong violet-blue luminescence with emission intensities up to 46 times more than the emission intensities observed prior to fluoride addition. Compounds 3 and 20 are demonstrated here as remarkable 'turn-on' fluoride sensors in tetrahydrofuran solutions.