Photochemistry and Photophysics of Coordination Compounds

More documents

Recommendations

Info

174 S. Campagna et al. containing 17 normal Ru chromophores and three RCs, the D + –A + chargeseparated state is formed, as shown by transient absorption spectroscopy. Emission at the Ru(II) chromophores was quenched by about 34% compared to the homopolymer containing 20 “normal” Ru chromophores. Energy transfer from the normal Ru chromophores to the RC sites was favored by – 0.1 eV. It was shown that about 50% of the charge-separated state was formed during the 7-ns laser pulse, indicating intrastrand sensitization, with the charge-separated state formed by direct excitation at the RC complex and by excitation to nonadjacent Ru chromophores followed by energy migration to the RC sites. In this system, 1.15 eV is stored in the charge-separated state and the efficiency of the process varies from 12 to 18% dependingonlaser irradiance, indicating excited-state annihilation at high irradiance. Charge recombination is similar to that of the “isolated” RC, but an additional longlivedtransient(formedinlowefficiency,about0.5%) was observed, which decayed by second-order kinetics with k = 48 M –1 s –1 .Thislong-livedtransient was attributed to polymers in which D + and A – were formed on different RC units, by invoking mechanisms in which electron transfer quenching by oxidative or reductive electron transfer in a RC site is followed by intrastrand hole or electron transfer to a second RC site [311]. 5.6 Photoinduced Collection of Electrons into a Single Site of a Metal Complex An essential property of natural photosynthesis is the collection of multiredox equivalents at specific sites. Indeed, all the important light energy storage
Photochemistry and Photophysics of Coordination Compounds: Ruthenium 175 processes require more than one electron to operate: for example, reduction of H + to H2 is bielectronic, and oxidation of oxygen in water to produce O2 is a four-electron process. Reduction of CO2 to the high-energy content glucose species is also a multielectron process. Whereas artificial systems capable of performing photoinduced charge separation have been reported, species able to collect, by successive photoinduced processes, more than one single electron (or hole) in one specific site of their structure are very rare. These species differ from polymers or dendritic species, which are also able to reversibly store more than one single electron (or hole) in their structure (in several, roughly identical, but spatially separated sites), since the accumulated charges should be located in a single subunit and, at least in principle, could be more easily delivered simultaneously to a unique substrate. A breakthrough in this field was the study of the two dinuclear Ru complexes 51 and 52 [312]. These complexes are indeed able to collect two electrons (and two protons) and four electrons (and four protons), respectively, within their bridging ligand moieties upon successive light excitation and in the presence of sacrificial donor species. In a typical (schematized) sequence of events involving 51: (1) light excitation produces a MLCT state involving the bpy-like subunit of the bridge; (2) a charge shift takes place from the bpy-like bridge moiety to the inner, phenazine-like portion of the bridge, so producing a sort of charge-separated state; (3) the sacrificial donor, a triethylamino (TEA) species, reduces the Ru(III) center, so restoring the chromophore; (4) the reduced central moiety of the bridge adds a proton (originated from irreversible TEA oxidation), so reaching charge neutrality; and (5) the sequence of events 1–4 is repeated and two electrons and two protons are collected [312]. However, a recent refinement of the ultrafast spectroscopic results has evidenced that the product of step 2, initially identified as a sort of charge-separated state [313], receives a significant contribution also from a bridge-centered triplet state [314]. The overall process is perfectly reversible, and 51 is fully restored on leaving molecular oxygen reaching the complex [312]. For 52, the formerly described sequence of events is repeated four times, thanks to the presence of the quinone subunits responsible for the addition of two extra electron/proton couples [312]. All the various steps of the multielectron processes occurring in 51 have also been characterized by UV/Vis spectroscopy and each intermediate has a unique
Page 1 and 2:
280 Topics in Current Chemistry Edi
Page 3 and 4:
Photochemistry and Photophysics of
Page 5 and 6:
Volume Editors Prof. Vincenzo Balza
Page 7 and 8:
Topics in Current Chemistry Also Av
Page 9 and 10:
X Preface nation Compounds. The ven
Page 11 and 12:
Contents Photochemistry and Photoph
Page 13 and 14:
Top Curr Chem (2007) 280: 1-36 DOI
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Top Curr Chem (2007) 280: 37-67 DOI
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
70 N. Armaroli et al. (e.g. catenan
Page 83 and 84:
72 N. Armaroli et al. can be classi
Page 85 and 86:
74 N. Armaroli et al. Fig. 2 Qualit
Page 87 and 88:
76 N. Armaroli et al. Fig. 3 Theblu
Page 89 and 90:
78 N. Armaroli et al. In the CuA mi
Page 91 and 92:
80 N. Armaroli et al. pseudo-rotaxa
Page 93 and 94:
82 N. Armaroli et al. Fig. 11 Relat
Page 95 and 96:
84 N. Armaroli et al. Fig. 13 Absor
Page 97 and 98:
86 N. Armaroli et al. leading to a
Page 99 and 100:
88 N. Armaroli et al. Fig. 18 Trans
Page 101 and 102:
90 N. Armaroli et al. Fig. 20 Ligan
Page 103 and 104:
92 N. Armaroli et al. Fig. 22 Ligan
Page 105 and 106:
94 N. Armaroli et al. tionalized de
Page 107 and 108:
96 N. Armaroli et al. Fig. 24 Absor
Page 109 and 110:
98 N. Armaroli et al. prisingly, PP
Page 111 and 112:
100 N. Armaroli et al. A different
Page 113 and 114:
102 N. Armaroli et al. Cuprous clus
Page 115 and 116:
104 N. Armaroli et al. Fig. 32 Sche
Page 117 and 118:
106 N. Armaroli et al. Fig. 34 A te
Page 119 and 120:
108 N. Armaroli et al. which are va
Page 121 and 122:
110 N. Armaroli et al. Acknowledgem
Page 123 and 124:
112 N. Armaroli et al. 58. Miller M
Page 125 and 126:
114 N. Armaroli et al. 123. Armarol
Page 127 and 128:
Top Curr Chem (2007) 280: 117-214 D
Page 129 and 130:
Page 131 and 132:
Page 133 and 134: Photochemistry and Photophysics of
Page 183: Photochemistry and Photophysics of
Page 225 and 226: Top Curr Chem (2007) 280: 215-255 D
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
258 Author Index Volumes 251-280 Be
Page 269 and 270:
260 Author Index Volumes 251-280 Er
Page 271 and 272:
262 Author Index Volumes 251-280 Je
Page 273 and 274:
264 Author Index Volumes 251-280 Me
Page 275 and 276:
266 Author Index Volumes 251-280 Sa
Page 277 and 278:
268 Author Index Volumes 251-280 Vi
Page 279 and 280:
Subject Index Alkyne bridges 148 An
Page 281:
Subject Index 273 Rh(III) cyclometa
show all

Photochemistry and Photophysics of Coordination Compounds

Create successful ePaper yourself

Delete template?

Save as template?