Photophysics of Singlet and Triplet Intraligand Excited States in [ReCl(CO)3(1-(2-pyridyl)-imidazo[1,5-伪]pyridine)] Complexes

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• 作者：Ana Mar铆a Blanco-Rodr铆guez ; Hana Kvapilov谩 ; Jan S媒kora ; Michael Towrie ; Carlo Nervi ; Giorgio Volpi ; Stanislav Z谩li拧 ; Anton铆n Vl膷ek ; Jr.
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：April 23, 2014
• 年：2014
• 卷：136
• 期：16
• 页码：5963-5973
• 全文大小：564K
• 年卷期：v.136,no.16(April 23, 2014)
• ISSN：1520-5126

文摘

Excited-state characters and dynamics of [ReCl(CO)₃(3-R-1-(2-pyridyl)-imidazo[1,5-伪]pyridine)] complexes (abbreviated ReGV-R, R = CH₃, Ph, PhBu^t, PhCF₃, PhNO₂, PhNMe₂) were investigated by pico- and nanosecond time-resolved infrared spectroscopy (TRIR) and excited-state DFT and TD-DFT calculations. Near UV excitation populates the lowest singlet state S₁ that undergoes picosecond intersystem crossing (ISC) to the lowest triplet T₁. Both states are initially formed hot and relax with 20 ps lifetime. TRIR together with quantum chemical calculations reveal that S₁ is predominantly a 蟺蟺* state localized at the 1-(2-pyridyl)-imidazo[1,5-伪]pyridine (= impy) ligand core, with impy 鈫?PhNO₂ and PhNMe₂ 鈫?impy intraligand charge-transfer contributions in the case of ReGV-PhNO₂ and ReGV-PhNMe₂, respectively. T₁ is predominantly 蟺蟺*(impy) in all cases. It follows that excited singlet and corresponding triplet states have to some extent different characters and structures even if originating nominally from the same preponderant one-electron excitations. ISC occurs with a solvent-independent (CH₂Cl₂, MeCN) 20鈥?0 ps lifetime, except for ReGV-PhNMe₂ (10 ps in CH₂Cl₂, 100 ps in MeCN). ISC is 200鈥?00 times slower than in analogous complexes with low-lying MLCT states. This difference is interpreted in terms of spin鈥搊rbit interaction and characters of orbitals involved in one-electron excitations that give rise to S₁ and T₁ states. ReGV-R present a unique case of octahedral heavy-metal complexes where the S₁ lifetime is long enough to allow for separate spectroscopic characterization of singlet and triplet excited states. This study provides an insight into dynamics and intersystem crossing pathways of low-lying singlet and triplet excited states localized at bidentate ligands bound directly to a heavy metal atom. Rather long ¹IL lifetimes indicate the possibility of photonic applications of singlet excited states.