Phosphorescence excitation mapping and vibrational spectroscopy of HC9N and HC11N cyanopolyynes in organic solvents

Abstract

Cyanopolyyne molecules, HC 9 N and HC 11 N, were isolated in solutions and UV, IR, and resonance Raman spectra were measured for the study of their electronic and vibrational properties. Strong signals were observed both in the IR and resonance Raman spectra for the stretching vibrational mode of the sp-hybridized linear carbon chain in the electronic ground state, i.e., σ 4 at 2141 cm -1 for HC 9 N and σ 6 at 2105 cm -1 for HC 11 N.Trapped in cryogenic solid acetonitrile matrix hosts at 20 K, transitions in phosphorescence, 3 Σ + → 1 Σ + , were observed for HC 9 N at 582.3 nm (0-0) and longer wavelengths and for HC 11 N at 643.7 nm (0-0) and longer wavelengths. Electronic transitions in the UV, 1 Σ + ← 1 Σ + , were elucidated by phosphorescence excitation mapping to observe asymmetric patterns with sharp emission-absorption features explainable by Shpolsky effects. For HC 9 N, three distinct trapping sites were discernible in solid acetonitrile, while the phosphorescence spectra were blurred in solid n-hexane. The observed phosphorescence lifetime of HC 9 N was longer than that of HighlightsPhosphorescence of cyanopolyyne molecules of HC 9 N and HC 11 N at 20 K Resonance Raman spectroscopy and IR spectra of HC 9 N and HC 11 N Solid acetonitrile or n-hexane matrix hosts provides multiple trapping sites

Phosphorescence of Hydrogen-Capped Linear Polyyne Molecules C8H2, C10H2 and C12H2 in Solid Hexane Matrices at 20 K

“…The observed lifetimes of 31 ms for C 8 H 2 , 8.4 ms for C 10 H 2 , and 3.9 ms for C 12 H 2 are comparable to the reported lifetimes of cyanopolyynes in solid rare gas matrices, i.e., 40 ms for HC 5 N [13,16], 8.2 ms for HC 7 N [15], and 3.9 ms for HC 9 N [18]. In solid organic matrices at 20 K, phosphorescence lifetimes of HC 9 N were ~9.7 ms in solid hexane and ~11.2 ms in solid acetonitrile, and the lifetime of HC 11 N was ~7.6 ms in solid acetonitrile [22]. These observations clearly show shorter lifetimes for larger species.…”

“…For the assignment of vibrational modes in Figure 9 and with emission and absorption wavelengths in solutions (triangles) [30]. Transition wavelengths of cyanopolyyne molecules, HC 2n+1 N, are plotted for comparison (closed markers) [22].…”

“…Very recently, photosyntheses were conducted using polyynic precursors of HC 5 N and C 4 H 2 co-condensed in solid rare gas matrices, and the detection of phosphorescence of HC 9 N was successful [18]. Using laser-ablated cyanopolyynes, the phosphorescence measurement was extended to HC 9 N and HC 11 N in solid organic molecules at 20 K as matrix hosts [22].…”

“…The formation of hydrogencapped polyyne molecules was confirmed up to C 26 H 2 by the laser ablation in decalin [25]. Spectroscopic characterization has so far been performed by UV absorption [9,10], IR absorption [11,12,19,22,26], Raman [17,24], and resonance Raman spectroscopy [27,28]. In relation to the formation mechanism, 1 H-NMR and 13 C-NMR were applied to polyynes, C 10 H 2 and C 12 H 2 [28], and cyanopolyynes, HC 7 N and HC 9 N [29].…”

“…The excitation wavelength of the forbidden transition of C10H2 in the solid hexane matrix in the present work (diamond) is plottedwith emission and absorption wavelengths in solutions (triangles)[30]. Transition wavelengths of cyanopolyyne molecules, HC2n+1N, are plotted for comparison (closed markers)[22].…”