Fullerene-indene adducts (ICMA & ICBA) in an astrochemical perspective part 1: chemical thermodynamics, stability and electronic absorption spectroscopy

Abstract

Both C₆₀ fullerene and indene were detected in certain astrophysical objects. It is then possible that these two molecules may react together in space forming adducts like indene-C₆₀ mono-adduct (ICMA) as well as the indene-C₆₀ bis-adducts (ICBA). In view of the potential detection of such adducts in space, the chemical thermodynamics of the reaction between C₆₀ and indene was analyzed using the thermochemical group increment approach. ICMA and ICBA were synthesized and their composition and stability was studied with thermogravimetric analysis and derivative thermogravimetry (TGA-DTG). ICBA and moreover ICMA resulted stable and strong adducts. In particular, the latter is stable up to 350 °C and this fact increases the chances to find it in space.

Furthermore, the retro Diels-Alder reaction was accurately studied on ICMA with differential scanning calorimetry (DSC) and an unusually high activation energy for the decomposition was determined and explained with the chemical thermodynamic data. The electronic absorption spectra of ICMA and ICBA were studied in n-hexane and the molar extinction coefficients of the main absorption bands have been determined. A possible way to detect such adducts is through electronic absorption spectroscopy, while the infrared spectroscopy of ICMA and ICBA is analyzed and discussed in the following second part of this work.

Keywords:

• C₆₀-indene adducts
• ICMA
• ICBA
• chemical thermodynamics
• TGA-DTG
• DSC
• UV-VIS
• astrochemistry

Additional information

Funding

We acknowledge support from State Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICINN) under grant PID2020-115758GB-I00. This article is based upon work from COST Action NanoSpace, CA21126, supported by COST (European Cooperation in Science and Technology).