Regioselective Hydrogenation of a 60-Carbon Nanographene Molecule toward a Circumbiphenyl Core

Regioselective peripheral hydrogenation of a nanographene molecule with 60 contiguous sp2 carbons provides unprecedented access to peralkylated circumbiphenyl (1). Conversion to the circumbiphenyl core structure was unambiguously validated by MALDI-TOF mass spectrometry, NMR, FT-IR, and Raman spectroscopy. UV–vis absorption spectra and DFT calculations demonstrated the significant change of the optoelectronic properties upon peripheral hydrogenation. Stimulated emission from 1, observed via ultrafast transient absorption measurements, indicates potential as an optical gain material.


S2
Nuclear Magnetic Resonance (NMR) spectra were recorded with a 5 mm PATXI 1 H-13 C/ 15 N/D z-gradient on the 850 MHz spectrometer with a Bruker Avance III system. High temperature NMR was recorded on Bruker Avance 500 MHz spectrometer.
For quantitative 1 H NMR measurements 512 transients were used with a 9.0 µs long 90° pulse and a 13600 Hz (16 ppm) spectral width together with a recycling delay of 8 s. The 13 C NMR (214 MHz) measurements were obtained with a J-modulated spin-echo for 13 C-nuclei coupled to 1 H to determine the number of attached protons with decoupling during acquisition. The used 90° pulse was 12.0 s long for carbon with a relaxation delay of 2 s.
The proton and carbon spectra were conducted in C2D2Cl4 and the spectra were referenced with the residual C2DHCl4 at 5.98 ppm (( 1 H)). The carbon spectra were referenced with the carbon signal of the solvent C2D2Cl4 at 74.19 ppm.
For the 2D NOESY experiments a spectroscopic width of 11900 Hz (14ppm) in both dimensions (f1 and f2) was used and the relaxation delay was 2.0 s. The mixing time used in the 2D NOESY was kept at 300ms. The spectroscopic widths of the homo-nuclear 2D COSY experiments were typically 11900 Hz in both dimensions (f1 and f2) with a relaxation delay of 2.0 s. The 2D correlation between proton and carbon used 1 H-13 C-HSQC (heteronuclear single quant correlation) edited 2 pulse program via double inept transfer for sensitivity S4 improvement and with decoupling during acquisition via trim pulses in the inept transfer and with multiplicity editing during the selection step. 1 JCH= 145Hz was used for optimizing observable intensities of cross peaks from multiple bond 1 H-13 C correlation.
Transient absorption experiments were performed with a home-built setup powered by an amplified Ti:sapphire laser (Coherent Libra) emitting 100-fs, 4-mJ pulses at 800 nm and 1 kHz repetition rate. The pump pulses were generated by an optical parametric amplifier, while the broadband probe pulses were obtained by white-light continuum generation in a sapphire plate. Pump and probe pulses were non-collinearly overlapped on the sample and the transmitted probe spectrum was measured by an optical multichannel analyzer working at the full 1-kHz laser repetition rate. The pump pulse was chopped at 500 Hz and the differential transmission (T/T) spectra were calculated for pairs of consecutive pulses and averaged over 300 pulse pairs.

Supplementary transient absorption information
In a typical TA experiment, a pump pulse populates the excited states while a broadband probe pulse investigates both the differential transmission ( − = ∆ ) and the lifetime of those states. When the probe is in resonance with the S0-S1 transition, its transmission will be enhanced by the pump-induced ground state depletion (ΔT/T > 0). For this reason, such a positive transient signal overlapping with ground state absorption is called photobleaching (PB). On the other hand, the probe transmission decreases when it is in resonance with excited states absorption (S1-Sn), and the resultant negative feature is called photoinduced absorption (PA). Finally, when the probe pulse is in resonance with the S1-S0 transition it will cause stimulate emission (SE) of a second photon, and the transient band associated with such an effect will be positive and, in general, overlapping with the emission spectrum.