Excited-state Engineering
To control the generation, evolution and fate of photo-excited states.
Light can generate energy, charge and chemical reactivity in molecules and materials. Once a molecule absorbs a photon, however, its excited state can follow competing pathways—emission, energy transfer, charge separation, annihilation, non-radiative decay or triplet formation. The central challenge is not simply to make a material absorb or emit light, but to control what happens after light is absorbed.
At OptoSpec Lab, we study the fate of photo-excited states—how they are generated, evolve, interact and can ultimately be harvested.
We combine molecular design, materials chemistry and time-resolved spectroscopy to uncover the fundamental mechanisms governing excited-state dynamics and develop new strategies to control them.
Our long-term goal is to translate fundamental photophysical insights into new design principles for molecular optoelectronics, photonic materials and energy conversion.
Research Artworks
RESEARCH DIRECTIONS @ OPTOSPEC LAB
1. TRIPLET HARVESTING
Making hidden excited states useful
Triplet excited states contain enormous opportunities for light emission, energy transfer and photochemical energy conversion, but their formation and utilization are governed by competing pathways.
We seek to understand how triplets are formed, how they evolve and how their energy can be efficiently harvested.
Our research explores:
TADF · Triplet–triplet annihilation · Triplet sensitization · Photocatalysis · Doping
· Phosphorescence · Energy transfer · Photochemical energy conversion · Triplet CT
Key question: How can we turn otherwise inaccessible triplet energy into useful function?
Reference: Sushree Suhani Puhan, Laxmipriya Dash and Palas Roy*; “Hydrogen-Bonding Environment Suppresses Thermally Activated Delayed Fluorescence” Chem. Sci. 17, 187 (2026) (Selected for Journal Cover Art)
2. NIR HARVESTING
Capturing the photons we cannot easily use
Near-infrared light represents a major part of the solar spectrum and is increasingly important in optical technologies. Yet many molecular optoelectronic systems cannot efficiently utilize these low-energy photons.
We develop molecular–nanomaterial interfaces that capture NIR photons and convert them into energetically useful excited states.
Our research explores:
Upconversion particles · NIR-to-visible conversion · Energy transfer mechanism
· Organic–inorganic interfaces · Two-photon absorption · NIR Photovoltaics
Key question: How can we make molecules and materials respond to photons that they normally cannot use?
Reference:
3. CONFINEMENT PHOTOPHYSICS
Confining molecules and materials to control excited states
Excited states do not exist in isolation. Their behaviour is strongly influenced by molecular packing, confinement, interfaces, hydrogen bonding and local environments.
We exploit these environments as a molecular design parameter to reshape excited-state pathways and discover photophysical behaviour that may not be accessible in dilute solution.
Our research explores:
Molecular confinement · Aggregates · Excimers · Charge-transfer states · TADF · RTP
· Tuning environments · Cascaded energy transfer · Optoleectronic breadboard · SBCS
Key question: Can we control excited-state behaviour simply by controlling the environment around a molecule?
Reference:
4. VIBRATIONALLY CONTROLLED PHOTODYNAMICS (VCP)
Steering excited-state dynamics through selective vibrational excitation
We investigate how molecular vibrations influence excited-state dynamics. By selectively exciting specific vibrational modes and following their effects in real time, we explore how molecular motion controls energy flow, charge transfer, and photochemical pathways.
Selective Vibrational Excitation → Time-Resolved Observation → Mechanistic Understanding → Photodynamic Control
Our research explores:
ns-ms Method development · Symmetry breaking charge separation · Triplet charge transfer · Photoswitches · Proton transfer
Key question: Can we control photodynamics by selectively exciting specific molecular vibrational modes?
Reference: 1. Roy et al., J. Chem. Phys. 161, 074504 (2024). 2. Roy et al., J. Am. Chem. Soc. 146, 18, 12255 (2024). 3. Roy et al., J. Am. Chem. Soc. 145, 36, 19849 (2023). 4. Roy et al., Nat. Commun. 14. 1253 (2023).
Tools We Use
We combine molecular design, materials chemistry, spectroscopy and
photophysics to connect structure with excited-state behaviour.
Our experimental and computational approaches include:
Steady-state spectroscopy and microscopy
Time-correlated emission spectroscopy
Transient pump-probe/flash photolysis
Time-resolved Raman spectroscopy
Quantum-yield measurements
Computational photophysics
Temperature dependence
These tools allow us to follow processes occurring across multiple timescales
—from ultrafast molecular events to long-lived excited states.
From Fundamental Photophysics To Technology
Understand → Control → Harvest → Integrate
We first uncover the fundamental mechanisms that govern excited-state dynamics. We then use molecular structure, vibrational motion, confinement and interfaces to control these pathways and direct excited-state energy toward desired functions.
Our goal is to translate these fundamental insights into molecular and material platforms with controllable optoelectronic properties. We envision molecular optoelectronic breadboards—well-defined systems in which individual photophysical processes can be isolated, understood, controlled and integrated to establish new design principles for optoelectronic and energy-conversion technologies.
