The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 × 10⁻⁵⁰ cm⁴ s photon⁻¹ molecule⁻¹, measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.

The polarized infrared (400-4 000 cm- 1) absorption spectra of single crystals of the 03B1 form of (BEDT- TTF)2I3 are reported for the high temperature conducting phase at T = 300 K and for the low temperature semi- conducting one at T = 20 K. For comparison and to supplement the already available data, the conductivity spectra obtained by Kramers-Kronig transformation of polarized reflectance data (80-6000 cm-1, T = 300 K) are also reported. The structures superimposed on the broad absorptions due to electronic intra- and interband transitions are extensively discussed and attributed to the coupling of conduction electrons to totally symmetric intramolecular modes of BEDT-TTF involving the stretching of C=C and C2014S bonds. Such an assignment is based on Raman data and a preliminary normal coordinate analysis of neutral BEDT-TTF. The guidelines for the development of a quantitative microscopic model of vibrationally induced electron charge oscillations in 2-D organic conductors are presented. A qualitative discussion of the model allows us to account for the observed dichroism of the vibronic structures in room temperature 03B1-(BEDT-TIF)2I3. Comparison of the 300 K and 20 K spectra and a study of the temperature dependence of powder absorption spectra allow us to identify the spectral changes induced by the 135 K metal-insulator (M-I) transition. They are discussed in relation to possible structural changes accompanying the M-I transition. It is found that displacements of the BEDT-TTF molecules in the organic sheets are needed to account for the observed spectral changes.