σ-Metalation of tetracene can change the emission color of and introduce new structural dimensionality to the organic chromophore. Two synthetic entries to σ-metallotetracenes have been explored, leading to emissive mononuclear (Ph 3 PAu I )-tetracene (1) and cis-[Br(Et 3 P) 2 Pt II ]-tetracene (2) and binuclear (R 3 PAu I ) 2 -tetracenyldiacetylide (R = Ph (4), Me ( 5)) and trans-[I(Et 3 P) 2 Pt II ] 2tetracenyldiacetylide (6). Metalation can lower the emission energy of tetracene up to 0.53 eV. The X(Et 3 P) 2 Pt II group (X = Br, I) has stronger perturbations on the tetracenyl ring than the R 3 PAu I group. σ-Metalation also leads to different crystal packing of the complexes and thus arrangements of the tetracenyl rings. Aurophilic attraction operates in 5, leading to self-assembly of the molecules into a novel honeycomb structure composed of helical Au I chains. In contrast to the other complexes, the crystal of 5 is not emissive, possibly due to efficient exciton delocalization.

Homobichromophoric platinum(II) complexes containing tetracenyl rings (T-Pt-T) and pentacenyl rings (P-Pt-P) were synthesized by Sonogashira coupling between trans-[Pt(PEt 3 ) 2 I 2 ] and 5-ethynyl-12-[(triisopropylsilyl)ethynyl]tetracene (T-SiH) and 6-ethynyl-13-[(triisopropylsilyl)ethynyl]pentacene (P-SiH), respectively. A heterobichromophoric complex consisting of tetracenyl and pentacenyl rings (T-Pt-P) was generated by coupling P-SiH and platinated T-SiH. The homobichromophoric complexes were characterized by singlecrystal X-ray diffraction. The electronic absorption and emission spectra of the complexes were investigated. All the complexes displayed acene-based fluorescence. The emission spectrum of T-Pt-P showed dual emissions of the tetracenyl and pentacenyl rings. Monitoring the pentacenyl emission gave an excitation spectrum which resembled the absorption spectrum, suggesting the presence of intramolecular energy transfer from the singlet excited state of the tetracenyl ring to the singlet excited state of the pentacenyl ring.

A series of binuclear platinum complexes of pentacenyl-6,13-diacetylide with different auxiliary ligands were synthesized to probe the effect of metal coordination on electronic spectroscopy and photophysics, to determine the solid-state packing of the complexes, and to tune emission energy. The complexes with anionic, π-donating ligands showed absorption (687−696 nm) and fluorescence (710−726 nm) lower in energy than those with neutral, π-accepting ligands (662−666, 675−686 nm). Our work showed that coordination of Pt ions with π-donating anionic ligands to pentacenyl-6,13-diacetylide could move the fluorescence of the organic chromophore to the nearinfrared region (λ em 710−726 nm). The combined perturbations of alkynation and platination lowered the HOMO → LUMO transition up to 0.34 eV. ■ EXPERIMENTAL SECTIONGeneral Methods. All syntheses were carried out under a N 2 atmosphere. All the solvents used for synthesis and spectroscopic

A sequence-specific synthesis of trichromophoric energy cascades containing anthracenyl (A), tetracenyl (T), or pentacenyl (P) rings is achieved by coupling PtII ions and singly desilylated bis­(triiso­propyl­silyl­ethynyl)­acenes (acene = anthracene, tetracene, or pentacene). Four sequences, T-P-T, P-T-P, A-P-T, and A-T-P, are generated. Absorption spectra of the triads show intense bands due to the S0 → S1 transitions of the acenes. The A-P-T and A-T-P, being able to absorb strongly throughout the entire visible region, are rare examples of “black chromophores”. Different sequences are shown to have different emission fingerprints. Emission spectra of A-P-T and A-T-P show that excitation at the S0 → S1 band of A gives rise to emissions from the S1 excited states of A, T, and P, implying the presence of energy transfer from the excited state of A to those of T and P.

To understand how the PtII ion perturbs the electronic structures of tetracene, 10 dinuclear [X(Et3P)2PtII]2-5,12-diethynyltetracene complexes with different auxiliary ligands were synthesized. Interactions between the PtII ion and 5,12-diethynyltetracene were probed spectroscopically and computationally. The dinuclear [X(Et3P)2PtII]2-5,12-diethynyltetracene complexes exhibit red-shifted absorption and fluorescence in comparison with those of 5,12-bis(triisopropylsilylethynyl)tetracene, with the neutral complexes with π-donating auxiliary ligands showing a larger red shift than the cationic complexes with π-accepting ligands. Electronic structures of the complexes and effects of the metal ions and the ligands on the electronic transitions of the complexes were investigated by TD-DFT calculations, the results of which showed that the electronic structure of the 5,12-diethynyltetracene core is perturbed by π interactions with the Pt fragments, the extent of which depends on the energies of the dπ orbitals of the Pt fragments.