Novel push–pull dendrons with high excited state dipole moments. Synthesis and theoretical analysis of unusual “branched electron distribution”

• Novel push–pull dendrons with high excited state dipole moments were synthesized.
• The rigidity and high delocalization of dendrons promote charge transfer mechanisms.
• Delocalized push–pull dendron (8) exhibits an unusual branched electron distribution.
• High excited state dipole moments can be related to efficient photovoltaic processes.
• Solvatochromic method is a useful tool to estimate dipole moments in excited state.

The synthesis of novel highly delocalized push–pull dendrons is described. A modified protocol to conventional CC coupling reaction was used with moderate yields. The excited state dipole moments of synthesized dendrons were estimated by the solvatochromic model using the ETN polarity scale. In case of dendron of second generation with donor–acceptor groups, values around 23 D are obtained, denoting an efficient charge separation crucial in photovoltaic processes. From the theoretical analysis, there is a clear evidence of highly efficient electron delocalization in case of push–pull dendrons. The chosen theoretical model (M05-2X/cc-pVDZ) to describe the electronic behavior of the molecules under study was very precise in the estimation of dipole moments in excited state, with differences of 0.5–2.2 D, compared with the values obtained by the solvatochromic model.

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