2,3-Diphenylbutadiene and Donor−Acceptor Functionalized Derivatives:  Exploring the Competition between Conjugation Paths in Branched π-Systems

Abstract

2,3-Diphenylbutadiene and its donor-acceptor functionalized derivatives represent branched pi systems consisting of three overlapping linearly conjugated units, namely a 1,3-butadiene and two phenylethene subsystems. The evaluation of pi conjugation using a scheme based on the natural bond orbital analysis shows that the details of the structure of these compounds is governed by electron delocalization. The potential energy surface of 2,3-diphenylbutadiene shows two minima, each one representing a distinct combination of conjugation patterns. These minima are shown to be connected by a low-energy path with transition structures that have one conjugation path fully activated, while conjugation is completely disrupted along the other path. We will show that, in response to donor-accptor functionalization, the 2,3-diphenylbutadiene backbone will switch to other conformations, which come along with substantial changes in the electronic structure.

A Scheme for the Evaluation of Electron Delocalization and Conjugation Efficiency in Linearly π-Conjugated Systems

“…These observations prompted us to explore the evolution of π-conjugation in PA, PDA, and PTA. For that matter, we studied the response of selected physical observables to the length of the backbone, and related these observations to the evolution of the delocalization energy along the π-conjugated chain using a new scheme based on the natural bond orbital (NBO) analysis. − The NBO analysis was shown to be a useful tool for the investigation of π-conjugation in earlier work. ,− …”

A systematic analysis of the structure and (hyper)polarizability of donor-acceptor substituted polyacetylenes using a Coulomb-attenuating density functional

“…[40][41][42] The objective of this paper is to provide a systematic investigation of the title compounds in order to devise rules connecting the structural features ͑in particular, chain length, donor/acceptor nature, and strength͒ to the resulting values for BLA, polarizability and hyperpolarizability. This is expected to provide useful structure/ property relationship, which can then be exploited to design systems with particular characteristics across one or multiple properties.…”

Photoinduced charge transport over branched conjugation pathways: donor–acceptor substituted 1,1-diphenylethene and 2,3-diphenylbutadiene

“…From a NBO population analysis Limacher and Lu ¨thi revealed a ground state effect on the p-electrons of compound DA2. 39 Butler-Ricks et al showed that in a donor-acceptor substituted diphenylethene the s-electron system may be dominant in charge transport. 16 In this respect it is of interest to compare the behavior of DA1 with that of data for molecules containing an N,N-dimethylaniline donor and a cyanophenyl acceptor separated by a bridge consisting of a single sp 3 carbon atom like compound 1C.…”

“…The calculated conformations are in agreement with geometries calculated by Limacher and Lu ¨thi. 39 The lowest energy structure of DA2 is thus different from the s-trans structure that was initially assumed, 32 and this might have a bearing on the understanding of the behaviour of the compound. In the butterfly-like s-gauche geometry DA2 possesses a compact structure, whereas in the s-trans conformation the geometry is extended.…”

“…37,38 MP2 and DFT calculations supported that this compound possesses an s-gauche minimum, and also revealed the presence of an s-trans minimum, which is somewhat (depending on the calculation method up to 1.47 kcal mol À1 ) higher in energy. 38,39 The structures of DA1 and DA2 were investigated with 6-311G** DFT/B3LYP calculations. In the optimized structure of DA1 (E = À481 363.76 kcal mol À1 ), the torsion angles between the double bond and the aniline and cyanophenyl groups amount to 36.91 and 41.31, respectively (Fig.…”