Synthesis and Characterization of Tetrachlorodiarylethyne-Linked Porphyrin Dimers. Effects of Linker Architecture on Intradimer Electronic Communication

Abstract

The effects of incorporating chloro groups at all ortho positions of a diphenylethyne linker that bridges the zinc and free base (Fb) components of a porphyrin dimer (ZnFbB(Cl(4))) have been investigated in detail via various static and time-resolved spectroscopic methods. The excited-state energy-transfer rate in ZnFbB(Cl(4)) ((134 ps)(-)(1)) is 5-fold slower than that in the corresponding dimer having an unsubstituted linker (ZnFbU, (24 ps)(-)(1)) but is only modestly slower than that in the dimer having o-methyl groups on the linker (ZnFbB(CH(3))(4), (115 ps)(-)(1)). The ground-state hole/electron-hopping rates in the oxidized bis-Zn analogues of all three dimers are much slower than the excited-state energy-transfer rates. There is no discernible difference between the hole/electron-hopping rates in the o-chloro- and o-methyl-substituted arrays. The similar ground- and excited-state dynamics observed for the o-chloro- and o-methyl-substituted arrays is attributed to the dominance of torsional constraints in mediating the extent of through-bond electronic communication. These constraints attenuate intradimer communication by restricting the rotation toward coplanarity of the phenyl rings of the linker and the porphyrin rings. Thus, the o-chloro groups on the linker decrease electronic communication via a steric, rather than purely electronic, mechanism.

Intramolecular and intermolecular energy transfers in donor-acceptor linear porphyrin arrays

“…Whether the energy transfer occurs through space or through bond interactions has been the subject of extensive studies. 8,[48][49][50][51][52][53] In both phenylethyne-linked and phenylenelinked Zn͑II͒ porphyrin and free-base porphyrin dyads, it was concluded that through bond interaction is the major contribution. 8,53 For the phenylene-linked porphyrin arrays, however, the calculated Förster rate and the observed rate are similar, 19 indicating that through space interaction is also significant.…”

The influence of phenylethynyl linkers on the photo-physical properties of metal-free porphyrins

“…Initially, we attempted to couple phenylethynylporphyrin 11 with 2,5-dimethoxy-1-bromobenzene in the presence of palladium (II) acetate. Unfortunately, the coupling was sluggish and little product was observed even after 100 h. Our next efforts involved the synthesis of 4-(2,5-dimethoxyphenylethynyl)benzaldehyde (20). Coupling of 4-ethynylbenzaldehyde [33] and 1-bromo-2,5-dimethoxybenzene in the presence of palladium(II) acetate gave aldehyde 20 as an air-sensitive solid in 29% isolated yield (Scheme 4).…”

“…Donors and acceptors have been separated by one or more porphyrin rings via diarylethyne [1,[7][8][9][10], ethyne [2][3][4][11][12][13][14] and polyethyne [3][4][5][6][15][16][17][18] linkers. Diarylethynes have been used as semi-rigid linkers [19,20] to connect multiple porphyrins for light-harvesting devices [1,21], molecular photonic wires [22], and optoelectronic gates [23]. Ethyne linkers have also been used to prepare porphyrin-based sensitizers for use in photodynamic therapy (PDT) [24][25][26][27].…”

Ground and Excited State Electronic Properties of Halogenated Tetraarylporphyrins: Tuning the Building Blocks for Porphyrin-based Photonic Devices

“…As part of this program we have initiated studies of simple diarylethyne-linked porphyrin dimers. The focus of these studies is to elucidate the mechanisms and factors that dictate the rates of excited state energy transfer and ground state hole/ electron hopping in these architectures [5][6][7][8][9][10][11]. Several of the key findings that have emerged from these studies are as follows.…”