A donor-acceptor dyad system involving tetrathiafulvalene (TTF) as donor attached by a flexible spacer to perylene-3,4:9,10-bis(dicarboximide) (PDI) as acceptor was synthesized and characterized. The strategy used the preliminary synthesis of an unsymmetrical PDI unit bearing an alcohol functionality as anchor group. Single-crystal analysis revealed a highly organized arrangement in which all PDI molecules are packed in a noncentrosymmetrical pattern. It was shown that the fluorescence emission intensity of the TTF-PDI dyad can be reversibly tuned depending on the oxidation states of the TTF unit. This behavior is attributed to peculiar properties of TTF linked to a PDI acceptor, which fluoresces intrinsically. Consequently, this dyad can be considered as a new reversible fluorescence-redox dependent molecular system.

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In this paper, we describe the second-order nonlinear optical properties of a series of 1,3-dithiole-based electron donor-acceptor systems incorporating proaromatic donor and spacer groups. Modification of the proaromaticity of the quinoid spacer gives rise to NLO-phores with mubeta values ranging from -2000 x 10(-)(48) esu to +3000 x 10(-)(48) esu. Quite surprisingly, compounds with a p-benzoquinoid spacer and a strong acceptor group show negative mubeta values, usually associated to zwitterionic ground states, and yet they are largely quinoid, as evidenced by crystallographic data and theoretical calculations. Progressive benzoannulation of the spacer and introduction of alkylsulfanyl substituents on the dithiole donor unit result in a shift to more positive mubeta values. DFT and ab initio calculations verify these empirical trends.

Symmetrical Donor-Acceptor-Donor (D-A-D) 2H-benzo[d][1,2,3]triazole derivatives have been designed by DFT calculations and prepared by a multistep synthetic protocol. The design strategy involved the identification of a suitable acceptor benzotriazole core and modification of the steric volume and donor strength of the branches in order to modulate the Intramolecular Charge Transfer (ICT) process and, consequently, the band gap. Self-assembly of the reported triazoles afforded organized supramolecular structures, the morphologies of which were visualized by SEM imaging. The outcomes demonstrated the effect that the donor moiety has on the emission properties and the morphologies of the aggregates. The aggregates that had a crystal-like structure, with smooth surfaces and flat end facets, exhibited optical waveguide behaviour with tunable colour emission. Depending on the initial design, the different emission wavelengths are related to the band gap of the benzotriazole derivatives.Keywords Tunable colour emission Waveguide Self-Assembly T-shaped 2H-benzo[d][1,2,3]triazole at the donor-acceptor heterojunction. The frontier molecular orbital profiles are shown in Figure 1.

Herein, we report the de novo synthesis and characterization of a series of substituted bithiophene derivatives as novel and inexpensive organic photocatalysts. DFT calculations were used to predict a priori their absorption spectra and redox potentials, which were then confirmed with empirical data. The photocatalytic activity of this novel class of organic photoredox catalyst was demonstrated in two visible-light mediated strategies for the CÀH functionalization of heteroarenes. The implementation of these strategies in a continuous-flow photomicroreactor afforded moderate to excellent yields within few minutes of reaction time. Due to their straightforward synthesis, low cost and good photocatalytic properties we believe that the proposed bithiophene derivatives could be employed as a new class of organic photoredox catalysts.

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