Synthesis and Characterization of Multinanometer-Sized Expanded Dendralenes with an iso-Poly(triacetylene) Backbone
摘要:
A series of [n]dendralenes (n = 3, 4, 8, 3b -d (Fig. 1)) expanded with buta-1,3-diynediyl moieties between the C=C bonds were prepared by repetitive acetylenic scaffolding of 3-(cyclohexylidene)penta-1,4-diyne building blocks (Scheme). These remarkably unstable iso-poly(triacetylene) (iso-PTA) oligomers were characterized by H-1- and C-13-NMR (Fig. 3 and Table 1), IR, and UV/VIS (Figs. 4 and 6 and Table 2) spectroscopy, as well as mass spectrometry (Fig. 2). The expanded [8]dendralene contains 40 C(sp)- and C(sp(2))-atoms in the backbone and represents the longest iso-PTA oligomer prepared to date. HOMO-LUMO Gap energies were determined as a function of oligomeric length (Fig. 5 and Table 3), providing insight into the degree of T-electron delocalization in these cross-conjugated chromophores. A continous drop in the HOMO-LUMO gap with increasing number of monomeric repeating units provides evidence that cross-conjugation along the oligomeric backbone is effective to some extent. The limiting HOMO-LUMO gap energy for an infinitely long, buta-1,3-diynediyl-expanded dendralene was extrapolated to about 3.3 - 3.5 eV. The conformational preferences of the expanded dendralenes were analyzed in semi-empirical calculations, revealing energetic preferences for planar or slightly twisted s-cis and 'U-shaped' geometries.
Synthesis and Characterization of Multinanometer-Sized Expanded Dendralenes with an iso-Poly(triacetylene) Backbone
摘要:
A series of [n]dendralenes (n = 3, 4, 8, 3b -d (Fig. 1)) expanded with buta-1,3-diynediyl moieties between the C=C bonds were prepared by repetitive acetylenic scaffolding of 3-(cyclohexylidene)penta-1,4-diyne building blocks (Scheme). These remarkably unstable iso-poly(triacetylene) (iso-PTA) oligomers were characterized by H-1- and C-13-NMR (Fig. 3 and Table 1), IR, and UV/VIS (Figs. 4 and 6 and Table 2) spectroscopy, as well as mass spectrometry (Fig. 2). The expanded [8]dendralene contains 40 C(sp)- and C(sp(2))-atoms in the backbone and represents the longest iso-PTA oligomer prepared to date. HOMO-LUMO Gap energies were determined as a function of oligomeric length (Fig. 5 and Table 3), providing insight into the degree of T-electron delocalization in these cross-conjugated chromophores. A continous drop in the HOMO-LUMO gap with increasing number of monomeric repeating units provides evidence that cross-conjugation along the oligomeric backbone is effective to some extent. The limiting HOMO-LUMO gap energy for an infinitely long, buta-1,3-diynediyl-expanded dendralene was extrapolated to about 3.3 - 3.5 eV. The conformational preferences of the expanded dendralenes were analyzed in semi-empirical calculations, revealing energetic preferences for planar or slightly twisted s-cis and 'U-shaped' geometries.
A series of [n]dendralenes (n = 3, 4, 8, 3b -d (Fig. 1)) expanded with buta-1,3-diynediyl moieties between the C=C bonds were prepared by repetitive acetylenic scaffolding of 3-(cyclohexylidene)penta-1,4-diyne building blocks (Scheme). These remarkably unstable iso-poly(triacetylene) (iso-PTA) oligomers were characterized by H-1- and C-13-NMR (Fig. 3 and Table 1), IR, and UV/VIS (Figs. 4 and 6 and Table 2) spectroscopy, as well as mass spectrometry (Fig. 2). The expanded [8]dendralene contains 40 C(sp)- and C(sp(2))-atoms in the backbone and represents the longest iso-PTA oligomer prepared to date. HOMO-LUMO Gap energies were determined as a function of oligomeric length (Fig. 5 and Table 3), providing insight into the degree of T-electron delocalization in these cross-conjugated chromophores. A continous drop in the HOMO-LUMO gap with increasing number of monomeric repeating units provides evidence that cross-conjugation along the oligomeric backbone is effective to some extent. The limiting HOMO-LUMO gap energy for an infinitely long, buta-1,3-diynediyl-expanded dendralene was extrapolated to about 3.3 - 3.5 eV. The conformational preferences of the expanded dendralenes were analyzed in semi-empirical calculations, revealing energetic preferences for planar or slightly twisted s-cis and 'U-shaped' geometries.