In all 3 data sources, psychotropic medications prescribed for preschoolers increased dramatically between 1991 and 1995. The predominance of medications with off-label (unlabeled) indications calls for prospective community-based, multidimensional outcome studies.
Youth psychotropic treatment utilization during the 1990s nearly reached adult utilization rates. Youth findings can be used to accurately assess the duration of treatment and unforeseen practice pattern changes, and to identify safety concerns.
Direct 355 or 532 nm light excitation of TBAI 3 , where TBA is tetrabutyl ammonium, in CH 3 CN at room temperature yields an iodine atom, I • , and an iodine radical anion, I 2 -• . In the presence of excess iodide, the iodine atom reacts quantitatively to yield a second equivalent of I 2 -• with a rate constant of k ) 2.5 ( 0.4 × 10 10 M -1 s -1 . The I 2 -• intermediates are unstable with respect to disproportionation and yield initial reactants, k ) 3.3 ( 0.1 × 10 9 M -1 s -1 . The coordination compound Ru(bpz) 2 (deeb)(PF 6 ) 2 , where bpz is 2,2′-bipyrazine and deeb is 4,4′-(C 2 H 5 CO 2 ) 2 -2,2′-bipyridine, was prepared and characterized for mechanistic studies of iodide photo-oxidation in acetonitrile at room temperature. Ru(bpz) 2 (deeb) 2+ displayed a broad metal-to-ligand charge transfer (MLCT) absorption band at 450 nm with ε ) 1.7 × 10 4 M -1 cm -1 . Visible light excitation resulted in photoluminescence with a corrected maximum at 620 nm, a quantum yield φ ) 0.14, and an excited state lifetime τ ) 1.75 µs from which k r ) 8.36 × 10 4 s -1 and k nr ) 5.01 × 10 5 s -1 were abstracted. Arrhenius analysis of the temperature dependent excited state lifetime revealed an activation energy of ∼2500 cm -1 and a pre-exponential factor of 10 10 s -1 , assigned to activated surface crossing to a ligand field or MLCT excited state. Steady state light excitation of Ru(bpz) 2 (deeb) 2+ in a 20 mM TBAI acetonitrile solution resulted in ligand loss photochemistry with a quantum yield of 5 × 10 -5 . The MLCT excited state was dynamically quenched by iodide with K sv ) 1.1 × 10 5 M -1 and k q ) 6.6 ( 0.3 × 10 10 M -1 s -1 , a value consistent with diffusion-limited electron transfer. Excited state hole transfer to iodide was quantitative but the product yield was low due to poor cage escape yields, φ CE ) 0.042 ( 0.001. Nanosecond transient absorption was used to quantify the appearance of two photoproducts [Ru(bpz -)(bpz)(deeb)] + and I 2 -• . The coincidence of the rate constants for [Ru(bpz -)(bpz)(deeb)] + formation and for excited state decay indicated reductive quenching by iodide. The rate constant for the appearance of I 2 -• was about a factor of 3 slower than excited state decay, k ) 2.4 ( 0.2 × 10 10 M -1 s -1 , indicating that I 2 -• was not a primary photoproduct of excited state electron transfer. A mechanism was proposed where an iodine atom was the primary photoproduct that subsequently reacted with iodide, I • + I -f I 2 -• . Charge recombination Ru(bpz -)(bpz)(deeb) + + I 2 -• f Ru(bpz) 2 (deeb) 2+ + 2I -was highly favored, ∆G o ) -1.64 eV, and well described by a second-order equal concentration kinetic model, k cr ) 2.1 ( 0.3 × 10 10 M -1 s -1 .
The synthetic route and properties of three 2D hybrid organic/inorganic lead iodide perovskite materials are reported. The 2D perovskites were synthesized from the reaction between PbI 2 and the di-cations of 1,4diaminobutane, 1,6-diaminohexane, and 1,8-diaminooctane. The resulting products were [NH 3 (CH 2 ) 4 NH 3 ] PbI 4 (BdAPbI 4 ), [NH 3 (CH 2 ) 6 NH 3 ]PbI 4 (HdAPbI 4 ), and [NH 3 (CH 2 ) 8 NH 3 ]PbI 4 (OdAPbI 4 ). Structural characterization shows that two dimensional perovskite structures were formed with inorganic structural planes separated by organic layers. Absorption spectra show band gaps of 2.37 eV (BdAPbI 4 ), 2.44 eV (HdAPbI 4 ), and 2.55 eV (OdAPbI 4 ). The 2D perovskite materials were investigated as light absorbing materials in solid state solar cells.The best performing material under moist, ambient conditions was BdAPbI 4 (1.08% efficiency), which was comparable to methylammonium Pb(II) iodide (MAPbI 3 ) solar cells (2.1% efficiency) manufactured and studied under analogous conditions. When compared to MAPbI 3 , the 2D materials have larger band gaps and lower photoconductivity, while BdAPbI 4 based solar cells shows a comparable absorbed photon-to-current efficiency as compared to MAPbI 3 based ones. † Electronic supplementary information (ESI) available: Tables S1-S4 including atomic parameters of the structure of the three new materials, Fig. S1 and S2, two 2D structures of butyl 1,4-diammonium lead iodide and octyl 1,8-diammonium lead iodide along the three crystallographic axes. Tables S5-S11 and Fig. S3-S9 describe structural and photochemical characterization. CIF les for the structures are available at the Cambridge Crystallographic Data Center (CCDC) referring to the deposition numbers 1420433 and 1420434 for HdAPbI 4 and OdAPbI 4 , respectively. See
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