Carbon Nanohoops: Excited Singlet and Triplet Behavior of Aza[8]CPP and 1,15-Diaza[8]CPP

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 119; no. 29; pp. 8083 - 8089
• Main Authors: Hines, Douglas A, Darzi, Evan R, Hirst, Elizabeth S, Jasti, Ramesh, Kamat, Prashant V
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23.07.2015
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.5b04404

The excited state properties of two nitrogen-doped cycloparaphenylene molecules, or carbon nanohoops, have been studied using steady-state and time-resolved absorption and emission spectroscopies. Quantum yield of fluorescence (Φf = 0.11 and 0.13) and intersystem crossing (Φisc = 0.45 and 0.32) were determined for aza[8]­CPP and 1,15-diaza[8]­CPP, respectively. We also present the proton transfer reaction between trifluoroacetic acid and the nitrogen-doped nanohoops, which resulted in significant modifications to the steady-state absorption and emission spectra as well as the triplet–triplet absorption spectra. From fluorescence quenching data we determine the equilibrium constant for the proton transfer reaction between aza[8]­CPP (K eq = 1.39 × 10–3) and 1,15-diaza[8]­CPP (K eq = 2.79 × 10–3) confirming that 1,15-diaza[8]­CPP is twice as likely to be protonated at a particular concentration of trifluoroacetic acid.