Saptarsi Mondal Ultrafast & multidimensional IR spectroscopy
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RESEARCH / ■ THEME V · COMPLETED · COLLABORATIVE

Weak noncovalent interactions and functional materials

My doctoral work examined whether interactions weaker than conventional hydrogen bonds can nevertheless organise liquids in experimentally measurable ways. Infrared spectroscopy and molecular dynamics connected the observed spectra to liquid structure, while quantum-chemical calculations and atoms-in-molecules analysis characterised the underlying interactions. Fluorescence upconversion and time-correlated single-photon counting provided complementary dynamical information.

Interactions weaker than a conventional hydrogen bond, from organic fluorine and fluorous dispersion in liquids to charge-shifted contacts in atmospheric clusters and CO₂ binding in porous polymers.

This is where I learned the habit that still governs how I work: never let a single technique carry a claim on its own. An infrared band shift is compatible with several structural stories. A simulation snapshot is only as good as its force field. A computed interaction energy says nothing about whether a bond path exists. Put the four together and the claim either survives or it does not.

The single-author carbonyl sulfide paper is the clearest example. The obvious reading of OCS hydration is a conventional hydrogen bond to the oxygen. The topological analysis showed something different: electron density shifting into the antibonding orbitals of OCS, producing charge-shifted sulfur–oxygen and carbon–oxygen contacts that a conventional hydrogen-bond picture would have missed entirely.

I also contributed to materials chemistry projects with groups at IACS and elsewhere. There I supplied the quantum-chemical and computational analysis that explained selectivity and binding; my collaborators carried out the synthesis, characterisation and performance measurements.

Methods

  • FTIR and Raman spectroscopy
  • GROMACS molecular dynamics simulation
  • Ab initio and DFT calculation
  • Atoms in molecules topological analysis
  • Fluorescence upconversion and TCSPC

Publications in this theme

20 records → publications
Why it matters
Organic fluorine, dispersive fluorine–fluorine contacts and charge-shifted interactions sit below the threshold where standard hydrogen-bond descriptions apply, yet they determine why fluorinated alcohols stabilise proteins, why perfluorinated solutes self-aggregate, and how atmospheric molecules take on their first water molecules. These are the interactions that shape solvation when the strong ones are absent.
My contribution
This was my doctoral programme and it produced fourteen publications. I showed that organic fluorine acts as a weak but genuine hydrogen-bond acceptor that restructures bulk fluorinated alcohols; that dispersive fluorine–fluorine interactions, not hydrogen bonding, govern solvation dynamics around perfluorinated solutes; and, in a single-author paper, that water binds carbonyl sulfide through charge-shifted noncovalent interactions driven by electron density shifting into OCS antibonding orbitals.
What we found
A single fluorine substitution on ethanol switches water's preferred binding site and reorients the surrounding water molecules. Perfluorination slows solvation response by roughly threefold through dispersion rather than hydrogen bonding. Hydration of carbonyl sulfide proceeds through sulfur–oxygen and carbon–oxygen charge-shifted contacts, with the first solvation shell closing at four water molecules. Separately, in collaboration with materials chemistry groups, I supplied the computational analysis showing how porous organic polymers achieve selective CO₂ capture and how sulfur and nitrogen coordination sequesters mercury from water.
Where it goes next
This line of work is largely complete. Its methods, particularly the combination of infrared measurement with topological analysis of the computed electron density, carry forward into how I assign and interpret interfacial spectra.

Where this work was done

Presented at

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