Push-pull systems, in which the proaromatic 4H-pyranylidene electron donor is conjugated with a dicyanomethylene acceptor through a quinoid thiophene as (part of) the electron relay, have been prepared, and their properties have been compared to those of a parent compound featuring an aromatic thiophene moiety. Different experimental techniques (X-ray diffraction, ¹H NMR, IR, Raman, UV-vis, cyclic voltammetry, spectroelectrochemistry, and NLO measurements) combined with theoretical calculations have been used for the study of the chromophores. Quinoidal derivatives, although neutral, show strongly polarized structures, with positive μβ values and a progressive increase of the intramolecular charge transfer (ICT) on lengthening the π-spacer. Comparison between compounds that only differ in the character (quinoid or aromatic) of the thiophene unit shows a more efficient ICT for the quinoid thiophene-containing chromophore, which influences the second-order NLO response. Furthermore, the thienyl ring has been also found to play a significant role in the ICT process for the analogous aromatic derivative.

Chromophores bearing a 2-dicyanomethylenethieno[3,2-b]thiophene moiety in their quinoidal form have been synthesized, exploring for the first time the reactivity of this system towards aldehydes. Their ground state polarization and linear and second-order nonlinear optical (NLO) properties have been determined by a combined experimental and theoretical study, and compared to those of analogous compounds featuring an aromatic thienothiophene unit. Due to the gaining of aromaticity, quinoid systems have been found to display more polarized electronic ground states and higher NLO responses with respect to their aromatic counterparts.

The synthesis and characterization of a series of tetrathiafulvalenes (1–3) bearing a different number of 4′-cyanobiphenyl-4-yloxy side groups is reported. Compound 3 exhibits a nematic and a smectic A mesophase. In the smectic A phase a peculiar local biaxial order due to the unconventional molecular structure is proposed. A charge-transfer salt derived from 3, namely 3·I₅ , also shows mesogenic behaviour.

The formal [2 + 2] cycloaddition–cycloreversion (CA–CR) between 4-ethynyl-N,N-dimethylaniline and polyenic Donor–π-Acceptor (D–π-A) systems takes place to yield compounds bearing two donors and one acceptor. Structural, linear and second-order nonlinear optical (NLO) properties of the new molecules reveal the stronger polarization of these systems when compared to analogous merocyanines lacking the dimethylaminophenyl (DMA) ring.

Langmuir-Blodgett (LB) films of the novel amphiphilic ethylenedithiotetrathiafulvalene derivative [EDT–TTF–CH₂OC(O)C₁₇H₃₅, 5] assembled on a range of solid substrates have room temperature in-plane do conductivity values as high σ_rt= 10^–2–10^–3 S cm^–1 as deposited; iodine doping results in an immediate decrease in conductivity to values of σ_rt=ca. 10^–6 S cm^–1, which subsequently increases over a few hours to σ_rt=ca. 10^–3 S cm^–1, as a stable mixed-valence state is attained. The LB films have been characterized by ellipsometry, UV–VIS spectroscopy and cyclic voltammetry. By comparison with analogous long-chain TTF and BEDT–TTF derivatives, it appears that the carbonyl group in the side chain of 5 facilitates LB film formation, and the ethylenedithio bridge of 5 contributes to the unusually high conductivity of the as-deposited films, possibly due to the presence of non-bonded, intermolecular S—S interactions. Analogous derivatives of trimethyl-TTF and ethylenediseleno-TTF substituted with the same side-chain, i.e., triMe–TTF–CH₂OC(O)C₁₇H₃₅, 10, and EDS–TTF–CH₂OC(O)C₁₇H₃₅, 11, respectively, form LB films with significantly lower conductivity values than 5, both before and after iodine doping.