Optical and electronic properties of neutral and charged oligodiacetylene clustersPresented at the LANMAT 2001 Conference on the Interaction of Laser Radiation with Matter at Nanoscopic Scales: From Single Molecule Spectroscopy to Materials Processing, Venice, 3–6 October, 2001.

Abstract

The collective electronic oscillator (CEO) approach recently proposed by Mukamel, which is based on an INDO/S Hamiltonian in the framework of the time-dependent Hartree-Fock approximation, is used to investigate the effect of the supramolecular architecture on the photogenerated excitations in different aggregates of a large-sized oligodiacetylene. The method gives the transition energies and the corresponding one-electron transition density matrices directly, which allows one to analyze, in terms of electron-hole motions in real space, the electronic redistribution upon photon absorption. Electronic excitations depend strongly on the arrangement of the oligomer molecules in the cluster, appreciable interchain effects being obtained even when the arrangement of the oligomer molecules corresponds to a minimum interchain interaction. Interchain interactions give rise to new transitions whose oscillator strengths depend on the nature of the aggregate (neutral or charged), and which can significantly modify the optical properties of the isolated molecular system.

Triplet excitons in acyl- and alkyl-substituted polycarbazolyldiacetylenes: A spectroscopical and photophysical study

“…34 Probably the interchain distance, the nature of the side groups and the polarization effect of the medium play an important role in the ordering of the excited states, as has been recently observed in di-phenyl substituted polyacetylene. 8,35,36 Coming back to the spectral emission properties of the acyl-polymers reported in Fig. 2 ͑not corrected for self-absorption͒ we can note that the 0-0 emissions for thick and thin polyDPCHD were detected at 548.0 ͑2.257͒ and 546.0 nm ͑2.269 eV͒, respectively, followed by the 0-1 bands at 591.6 and 589.0 nm, and by the 0-2 emissions at about 613 and 610 nm.…”

“…In a previous paper, the role of interchain interactions has been discussed. 8 Here, the same approach will be used for the assignment of fine details in the spectra, such as the very weak band observed around 450 nm only for the polymers where a small el-ph interaction allows the observation of the even weakest features. Calculations based on the collective electronic oscillator ͑CEO͒ method for a 15 repeat unit neutral oligomers ͑see Ref.…”

“…Calculations based on the collective electronic oscillator ͑CEO͒ method for a 15 repeat unit neutral oligomers ͑see Ref. 8 for details͒ showed that the main absorption of the diacetylenic backbone is located at 2.45 eV, followed by other transitions of much lower oscillator strengths, of which the first allowed one is located at 2.79 eV. The analysis of these modes shows that the excitations of a linear conjugated chain resemble the vibrations of a string.…”

“…For several years our group has been interested in the preparation of diacetylenic monomers, their polymerization, 1,2 the study of their photophysical, [3][4][5][6][7] and electronic properties 8,9 as well as in the evaluation of their non linear optical ͑NLO͒ properties, [10][11][12] which are potentially suitable for photonic applications. 13 The nonlinear optical properties of these materials depend on the nature of the electronic excited states.…”

Hyperpolarizability density analysis of the enhancement of second hyperpolarizability of π‐conjugated oligomers by intermolecular interaction

“…A lthough the intermolecular interaction effects on the nonlinear optical (NLO) properties are known to be important, for example, through the control of conformation among monomers in macroscopic crystals [1], there have been a few studies on the active control of NLO properties of clusters or crystals by adjusting the intermolecular interactions such as intermolecular charge transfer (CT) and orbital overlap interaction [2][3][4][5][6][7][8][9]. In our previous paper [10], we elucidated that the intermolecular (cofacial) -orbital interactions significantly change the magnitude of the longitudinal second hyperpolarizability (␥), which is the microscopic origin of the third-order NLO properties, of isolated monomers using the -stacking dimer models composed of C 5 H 7 ϩ molecules.…”