Optical ON/OFF Switching of Intramolecular Photoinduced Charge Separation in a Donor−Bridge−Acceptor System Containing Dithienylethene

Bichromophoric perylene derivatives: energy transfer from non-fluorescent chromophores

The energy of excitation at non-fluorescent chromophores such as fluorenone and anthraquinone has been trapped by a fast energy transfer to the highly fluorescent perylene bisimides. To this end, anthraquinone, fluorenone and anthracene derivatives have been linked to the perylene bisimides by non-conjugating spacers and fluorescence quantum yield of such assemblies have been determined as a function of the wavelengths of excitation. Energy transfer in such assemblies is strongly influenced by the orientation of the two chromophores. This is of interest for the construction of fluorescence switches.

Regulating pi-conjugated pathways using a photochromic 1,2-dithienylcyclopentene

Linear pi-conjugation is reversibly re-routed by irradiation of a photochromic bis(terthiophene).

Photonic switching of photoinduced electron transfer in a dithienylethene-porphyrin-fullerene triad molecule

A dithienylethene (DTE)-porphyrin (P)-fullerene (C(60)) triad molecule in which intramolecular photoinduced electron transfer is controlled by the photochromic DTE moiety has been prepared. Irradiation of the molecule with visible light gives the open form of the dithienylethene (DTEo). Excitation of the porphyrin gives DTEo-(1)P-C(60), which undergoes photoinduced electron transfer with a time constant of 25 ps to generate DTEo-P(.+)-C(60)(.-). Irradiation with ultraviolet light produces the closed form of the dithienylethene (DTEc). Excitation of DTEc-P-C(60) yields DTEc-(1)P-C(60), whose porphyrin first excited singlet state is quenched in 2.3 ps by singlet-singlet energy transfer to DTEc, generating (1)DTEc-P-C(60) and precluding significant photoinduced electron transfer. Such highly reversible photonically controlled intramolecular photoinduced electron transfer may eventually be useful in the design of photonic or optoelectronic devices.

Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2''-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.

Synthesis and photoisomerization of dithienylethene-bridged diporphyrins

Dithienylethene-bridged diporphyrins 1-6 were prepared as photochemical switching molecules. Porphyrin and dithienylethene are directly linked in 1, and linked, respectively, through a 1,4-phenylene spacer in 2, through a 4-ethynylphenylene spacer in 3, and through a di-4-phenylethynylene spacer in 4, while meso-ethynylated porphyrin and dithienylethene are directly connected in 5 and linked through a 1,4-phenylene spacer in 6. Compounds 1, 2, and 5 do not undergo any photochemical isomerization, probably due to efficient quenching of the excited dithienylethene by the attached porphyrin moiety via intramolecular energy transfer. Compounds 4 and 6 undergo open-to-closed and closed-to-open photoisomerizations in quantum yields of 4.3 x 10(-)(2) and 1.8 x 10(-)(3), and 2.6 x 10(-)(3) and 7.5 x 10(-)(4), respectively, by irradiation with 313 and 625 nm light, which are considerably smaller than quantum yields of 0.52 and 3.8 x 10(-)(3) for reference dithienylethene molecule 7. The fluorescence of 4 was regulated in a reversible manner by the photoisomerization of the dithienylethene moiety. In addition, the absorption properties of the porphyrin in 6 changed in response to the photochromic reaction of the dithienylethene bridge.