Tetracene Molecules Research Articles

Epitaxial growth of tetracene on the Ag(1 1 0) surface

Thin film growth of tetracene on Ag(1 1 0) has been investigated by using scanning tunneling microscopy (STM). In the monolayer regime, the tetracene molecules formed islands of ordered structure, which is commensurate (4-fold periodicity) in the [ 1 1 ¯ 0 ] direction, but incommensurate in the [0 0 1] azimuth, with the substrate. All the tetracene molecules align regularly with their longer axes parallel to the [0 0 1] direction, and with their molecular planes parallel to the surface. At multilayer coverages, the tetracene molecules form a crystalline film in a novel 3D orthorhombic structure, with their orientations remained unchanged. Growth of tetracene on Ag(1 1 0) is in the layer-by-layer growth mode.

Exciton delocalization and superradiance in tetracene thin films and nanoaggregates.

The structure and dynamics of luminescent excitons in tetracene thin films and nanoaggregates are investigated using time-resolved spectroscopy and theoretical calculations. The orientation of tetracene's transition dipole moment along its short molecular axis leads to properties qualitatively different from those observed in aggregates of phenylene-vinylene and thiophene oligomers, despite similar crystal structures. The spectral shape, temperature dependence, and radiative lifetime are consistent with a short-lived superradiant exciton delocalized over approximately 10 tetracene molecules.

Quantum interference in polycyclic hydrocarbon molecular wires

Abstract The construction of devices based on molecular components depends upon the development of molecular wires with adaptable current–voltage characteristics. Here, we report that quantum interference effects could lead to substantial differences in conductance in molecular wires which include some simple polycyclic aromatic hydrocarbons (PAHs). For molecular wires containing a single benzene, anthracene or tetracene molecule a large peak appears in the electron transmission probability spectrum at an energy just above the lowest unoccupied orbital (LUMO). For a molecular wire containing a single naphthalene molecule, however, this same peak essentially vanishes. Furthermore, the peak can be re-established by altering the attachment points of the molecular leads to the naphthalene molecule. A breakdown of the individual terms contributing the relevant peak confirms that these results are in fact due to quantum interference effects.

Scanning tunnelling microscopy of tetracene onSi(100)-2 × 1

Scanning tunnelling microscopy (STM) has been used to follow the adsorption of tetracene molecules on theSi(100)-2 × 1 surface. Two distinct types of adsorption are indicated by filled state images but threetypes may be distinguished in empty state images. Molecules aligned both along andperpendicular to the silicon dimer rows can be observed. The calculated charge densitiesassociated with occupied and unoccupied orbitals near the Fermi level are compared withthe STM images. Possible bonding arrangements and their correlation with the STMimages are postulated.

Spontaneous alignment of tetracene molecules in 4He droplets

The polarization dependence of the laser induced fluorescence and absorption was investigated for single tetracene molecules embedded in 4He droplets having N ̄ 4=3×10 3–3×10 5 atoms. The measurements revealed an increase in the intensity up to 20% in the spectra, when the laser polarization vector was aligned parallel to the direction of the droplet beam as compared to the perpendicular alignment. This observation suggests a spontaneous alignment of the molecules in the laboratory frame. A mechanism of the molecular alignment in the pick-up process is proposed.

Structure of tetracene–argon and tetracene–krypton complexes from high resolution laser experiments at 450 nm

The partly rotationally resolved spectra of tetracene–Ar and tetracene–Kr were revisited. In a previous study it was not possible to assign experimental spectra. The spectra were obtained from high resolution laser experiments around 450 nm. With state of the art fast computers and recently developed software and algorithms we succeeded in explaining the observed spectra. Rotational constants of the complexes are obtained from which the structure of the clusters are deduced. It is found that the noble gas is located above the middle of one of the central benzene rings of the tetracene molecule with distances to the plane of 3.42 and 3.65 Å for Ar and Kr, respectively.

The formation of heterogeneous van der Waals complexes in helium droplets

The formation of the heterogeneous van der Waals complexes of tetracene with two and three argon atoms in helium droplets have been studied using the pick up technique. The laser-induced fluorescence spectra were measured with embedding of the chromophore tetracene molecule prior to the argon atoms and vice versa. The results indicate that once the Ar n complex is formed within the helium droplet it remains intact upon subsequent attachment of the tetracene molecule. This observation suggests a strategy of formation and study of larger hetero complexes where the possible number of structural isomers can be considerably reduced.

Hole-Burning Studies of the Splitting in the Ground and Excited Vibronic States of Tetracene in Helium Droplets

The laser-induced fluorescence spectra of single tetracene (C18H12) and pentacene (C24H14) molecules embedded in liquid HeN droplets (N ≃ 104) show sharp zero phonon lines (ZPL) (δν ≤ 0.2 cm-1), accompanied by weaker phonon wings (PW) on the blue side. The ZPL of tetracene is anomalously split into a doublet with a separation of 1.1 cm-1, whereas for pentacene, the ZPL is not split. Hole-burning measurements with two pulsed dye lasers and lifetime measurements indicate that inside He droplets the ground and excited states of tetracene are each split into two levels. The splitting is attributed either to the occupation of two nearly equivalent sites by localized helium atoms or to a tunneling of one or two localized helium atoms through the barrier in the double-well potential on the surface of the tetracene molecule.

Pump–probe study of the reconstruction of helium surrounding a tetracene molecule inside a helium droplet

The electronic spectra of single tetracene molecules and tetracene–Ar complexes embedded in large (≃103–104) superfluid helium droplets have been investigated with a pump–probe technique. New sharp (δν≈0.5 cm−1) red-shifted (Δν≈1–2 cm−1) features are obtained in the probe laser spectra indicating a rapid (Δt<20 ns) reconstruction of the He environment upon electronic excitation. These new structures are interpreted with a simple modified bubble-like model. Evidence for a rise in the droplet temperature induced by the pump laser pulse is obtained from a broadening of the phonon wing measured by the probe laser.

Spectral hole-burning of tetracene and tetracene—argon complexes in a supersonic jet

The fluorescence excitation spectra of the tetracene molecule and the van der Waals clusters tetracene·Ar itn with n=1,2,3, cooled in a supersonic free jet expansion have been obtained with a spectral hole-burning technique. The supersonic beam contained a mixture of clusters up to n=7. The influence on the intramolecular vibrations of tetracene up to vibrational excess energy of 1250 cm −1 was found to be very small. For the three smallest ( n=1–3) clusters a low-frequency vibration with a wavenumber of about 40 cm − was found and assigned to the motion of the Ar atom perpendicular to the molecular plane. A vibration with a wavenumber of 8 cm − corresponding to the motion parallel to the plane of the tetracene molecule was distincly observed only in the cluster containing a single Ar atom. It is shown that weak lines due to the minor species can be assigned unambiguously even if they are strongly overlapped by lines of another species.

Azimuthal orientation of tetracene adsorbed on Cu(110) single crystal surfaces

Angular resolved photoemission spectroscopy using synchrotron radiation from the BESSY storage ring has been employed to investigate the geometrical arrangement of tetracene molecules adsorbed on Cu(110) surfaces. By simple symmetry considerations based on dipole selection rules we find a perpendicular orientation of the molecules with their molecular planes aligned along the [1̄10] azimuth. Additionally, a c(4 × 2) structure has been observed by LEED.

Low temperature emission spectra of trapped tetracene pairs from ditetracene

Interacting pairs of tetracene molecules are prepared in a PMMA host matrix by photodecomposition of ditetracene at 15 K. Excitation and emission spectra of these pairs are red-shifted and broadened relative to those of isolated tetracene molecules under the same conditions. No differences are seen in the spectra of pairs formed from syn-ditetracene and from anti-ditetracene. The results suggest that these pairs of tetracene molecules are not in the parallel (sandwich) configuration and that a distribution of intermolecular distances and orientation is obtained. A large geometry change in the excited state, akin to excimer formation, is postulated to explain the fluorescence spectrum.

Radiationless transitions in p-terphenyl crystals doped with anthracene, tetracene and pentacene

The fluorescence spectra and lifetimes of anthracene, tetracene and pentacene molecules in a host p-terphenyl single crystalline lattice have been measured over the temperature range 10–300 K. At low temperatures the molecules occupy different sites in the host lattice: five for anthracene (O1, O2, O3, O4, O5), six for tetracene (O1, O2, A1, A2, A3, A4) and four for pentacene (O1, O2, O3, O4). The high-temperature fluorescence spectra are dominated by particular sites (O4/O5 for anthracene, A2/A4 for tetracene and O1/O2 for pentacene) and the temperature dependence of the fluorescence lifetime of these sites is recorded. Neither O4/O5 for anthracene nor A2/A4 for tetracene exhibit a marked temperature dependence whereas the lifetime of O1/O2 for pentacene decreases with increasing temperature with an activation energy of 60–90 cm–1. This temperature dependence is associated with an increased probability for intersystem crossing from O1/O2 to a triplet level (T2) of the pentacene molecule which is located at 16 960 ± 15 cm–1. For anthracene and tetracene T2 is inaccessible from all sites over the entire temperature range and for anthracene the short lifetime reflects the facile transfer of excitation from S1 to T1.

ChemInform Abstract: ENERGETICS AND INTRAMOLECULAR DYNAMICS OF THE ISOLATED ULTRACOLD TETRACENE MOLECULE IN ITS FIRST EXCITED SINGLET STATE

Chemischer InformationsdienstVolume 13, Issue 1 Physical Organic Chemistry ChemInform Abstract: ENERGETICS AND INTRAMOLECULAR DYNAMICS OF THE ISOLATED ULTRACOLD TETRACENE MOLECULE IN ITS FIRST EXCITED SINGLET STATE A. AMIRAV, A. AMIRAVSearch for more papers by this authorU. EVEN, U. EVENSearch for more papers by this authorJ. JORTNER, J. JORTNERSearch for more papers by this author A. AMIRAV, A. AMIRAVSearch for more papers by this authorU. EVEN, U. EVENSearch for more papers by this authorJ. JORTNER, J. JORTNERSearch for more papers by this author First published: January 5, 1982 https://doi.org/10.1002/chin.198201053AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue1January 5, 1982 RelatedInformation

Out-of-plane vibrations of isolated tetracene and pentacene molecules

The electronic spectra of tetracene and pentacene have been studied in a supersonic jet apparatus. Both molecules show excitation to out-of-plane B1g(see-saw) vibrations.

Tetracene-argon van der waals molecules

Expansion of tetracene vapour with excess argon carrier gas through a nozzle of a supersonic jet apparatus permits the controlled formation of (C 18H 12)Ar n molecules. These have been studied by laser fluorescence techniques in the 450 nm region of the spectrum corresponding to excitation of the parent tetracene molecules to the 1B 1u electronic state. We have been able to observe up to the n = 10 complex and have identified three different binding sites on the tetracene framework. From the resolved fluorescence spectra of these species one obtains an upper limit of the van der Waals binding energy of 314 cm −1 in the upper electronic states and 274 cm −1 in the ground state. These resolved spectra also exhibit features identified as due to the tetracene-argon stretching vibration giving a value of 36.5 ± 2 cm −1 for the lowest transition in the ground state of (C 18H 12)Ar.

Energetics and intramolecular dynamics of the isolated ultracold tetracene molecule in its first excited singlet state

In this paper we report the results of an experimental study of the energetics and intramolecular dynamics of the first electronically excited S1 singlet state of tetracene (C18H12) seeded in supersonic expansions of rare gases. Internal cooling of tetracene in supersonic expansions of Ar down to rotational temperatures TR∼5–7 K and vibrational temperatures TV&amp;lt;50 K can be accomplished at moderately low stagnation pressures p = 100–200 Torr of Ar, Kr, and Xe when expanded through a D = 150 μ nozzle. We have interrogated the fluorescence action spectra, the energy-resolved fluorescence, and the time-resolved fluorescence of the ultracold, isolated, bare, large molecule for excess vibrational energies EV = 0–4000 cm−1 above the electronic origin of the S1 state. The electronic origin of the S0(1A1g)→S1(1B2u) transition located at 22 360 cm−1 exhibits a partially resolved B-type rotational structure, which concurs with the short axis polarization of this transition. We were able to identify nine totally symmetric alg fudamentals and three vibronically induced b 3g fundamentals in the vibrational structure of S1 in the energy range EV = 0–1600 cm−1. The vibrational structures of the S1 state and of the S0 state in the isolated molecule are in good agreement with the mixed crystal data, indicating small medium effects on the low-energy vibrational level structure. Information on the shift and distortion of the potential surface of the S1 state relative to S0 was inferred from frequency changes and from Franck–Condon vibrational overlap factors. We have investigated two classes of nonreactive dynamic processes in the S1 manifold, involving intrastate anharmonic mixing (IAM) and interstate electronic relaxation (ER). IAM was explored by the observation of the onset for spectral congestion in the absorption spectrum which marks the onset of the vibrational quasicontinuum, as well as by the observation of band splitting in the energy-resolved emission spectra which marks the onset of IAM. The threshold for IAM in the S1 state of tetracene is exhibited at EV?1000 cm−1 below the onset of the vibrational quasicontinuum, which occurs at EV?1600–1800 cm−1. These observations provide a firm basis for the identification of three energy regions for IAM in the S1 manifold of this large molecule, i.e., the sparse level structure (EV = 0–1000 cm−1), the intermediate level structure (EV = 1000–1600 cm−1), and the statistical limit (EV≳1800 cm−1). Information concerning ER in the S1 manifold was obtained from the experimental decay lifetimes τ of photoselected states at excess vibrational energies EV = 0–4000 cm−1. Excitations in the sparse vibrational level structure in the range EV = 0–1200 cm−1 results in a retardation of the ER rate relative to its value for the electronic origin; this blocking of the ER rate for low EV is attributed to S1→T1 intersystem crossing, which is characterized by a low electronic energy gap. Excitation in the vibrational quasicontinuum results in the τ values which are practically independent of EV with τ = 4.5±0.5 nsec in the range EV = 2000–4000 cm−1. This observation cannot be reconciled with the notion of effective energy redistribution among all vibrational modes and is tentatively attributed to the effects of selective intrastate anharmonic mixing which involves a subset of the vibrational states.

Microscopic solvation effects on excited-state energetics and dynamics of aromatic molecules in large van der Waals complexes

In this paper we report the results of an experimental study of the formation kinetics, excited-state energetics, interstate electronic relaxation, and intrastate nuclear dynamics in electronically–vibrationally excited states of van der Waals molecules, consisting of a tetracene (T) molecule and rare-gas (R) atoms. The TRn molecules were synthesized in seeded supersonic jets. Excited-state energetics and dynamics of TRn molecules were explored by laser spectroscopy in supersonic expansions, interrogating the fluorescence action spectra, the energy-resolved emission, the relative emission quantum yields, and the time-resolved emission. Spectroscopic diagnostic methods for the identification and characterization of the chemical composition of TRn complexes involved the dependence of the spectral features on the identity of the rare gas, an intensity conservation rule for the intensities of TArn and of T, the pressure dependence of the intensity of the bare T molecule, the pressure dependence of the intensity of the spectral features of the TRn molecules, and their order of appearance. We were able to identify the following 13 molecules: TArn(n = 1,2,⋅⋅⋅7), TKrn(n = 1,2,3,4), and TXen (n = 1,2), and to assign the spectral features which correspond to the vibrationless S0→S1 excitations of these molecules. For TAr1, TAr2, TAr3, TKr1, and TKr2, a single spectral feature corresponding to each molecule was observed, providing evidence against the existence of distinct chemical isomers of these molecules. For TKr3 and TKr4 a multiple spectrum consisting of several bands for each chemical composition was observed, which was tentatively assigned to chemical isomers of these molecules. The TXe1 and TXe2 spectra reveal, in addition to a main band, weak satellites which were tentatively attributed to vibrational structure. The red spectral shifts of the vibrationless and the 314 cm−1 S0→S1 electronic excitations of all TRn molecules from the corresponding excitation of the bare T molecule are dominated by dispersive interactions, the red shifts for the TR1 (R = Ne, Ar, Kr, and Xe) molecules being proportional to the polarizability of the R atom. The spectral shifts of TRn molecules are not additive per added atom, the violation of the additivity law being attributed to the occupation of geometrically inequivalent sites by the R atoms. To demonstrate the universality of van der Waals molecule formation by large aromatics, we have studied the energetics of T(N2)n (n = 1–3) molecules and obtained preliminary spectroscopic data on T(C6H6) and T(H2O). We have studied, subsequently, microscopic solvent effects on electronic relaxation from the vibrationless S1 state and from the 314 cm−1 vibrational excitation of this state of tetracene embedded in well characterized TRn complexes. The decay lifetimes τ of the vibrationless S1 electronic state of TNe1 and TArn (n = 1,2,...,7) molecules are in the range τ = 17±2 to 34±3 nsec, being close to or somewhat higher than the lifetime τ0 = 19±2 nsec of the electronic origin of the bare T molecule. The lifetimes of the vibrationless level of TKr1, TKr2, TKr3, and TKr4 molecules (τ = 6±1 to 8±1 nsec) and of TXe1 and TXe2 complexes (τ∼1.5 nsec) reveal a dramatic shortening relative to τ0, which is attributed to the heavy atom enhancement of S1→T1 crossing. The lifetimes of TKrn (n = 1–4) and of TXen are practically independent of the coordination number, whereupon the heavy atom enhancement of intersystem crossing in these systems essentially originates from T–Kr and T–Xe single-pair interactions. We also explored some effects of intrastate nuclear dynamics in the S1 state of TArn and of TKrn molecules. We have demonstrated that the 314 cm−1 vibrational excitations of TAr1 and of TKr1 do not result in vibrational predissociation on the (nsec) time scale of the excited-state lifetime, the reactive channel being presumably closed. The heavy atom effect on the decay lifetimes of TKrn was utilized to search for the onset of vibrational predissociation, which is exhibited at excess vibrational energies of 1250 cm−1 above the electronic origin.

Spectroscopy of large molecules in inert gas clusters

Aromatic hydrocarbons provide nucleation centers for the formation of clusters of inert gases in high-flow supersonic beams. Large clusters of Ar, each containing a single tetracene (T) molecule, were prepared by supersonic expansion of the seeded gas at pressures p = 3000–13000 Torr and interrogated by laser-induced fluorescence spectroscopy Evidence is reported for homogeneous line broadening of large TAr n clusters prepared at p⪖ 8000 Torr.

Energy transfer in amorphous anthracene-tetracene films

Sensitized fluorescence in amorphous anthracene-tetracene layers formed by vacuum-sublimation onto 77 K substrates is investigated as a function of tetracene concentration, sample temperature and annealing conditions. It is found that in the temperature range 77 to 130 K host-guest energy transfer in unannealed samples occurs by Förster long range coupling between anthracene excimers and single tetracene molecules. The experimental transfer distance R 0 = 28.7 ± 2.3 Å is in fair agreement with the calculated value R 0, theor = 25.8 ± 1.6 Å. Population of the excimer-forming sites must involve singlet exciton motion through the host matrix.