Time-resolved Techniques Research Articles

Study of FRET between Zn-Cu-In-S/ZnS core/shell quantum dots-Cresyl violet dye system

This study reports the fluorescence resonance energy transfer between Zn-Cu-In-S/ZnS core–shell quantum dots and Cresyl Violet dye. The quenching of Zn-Cu-In-S/ZnS core–shell QD (donor) emission and lifetime and simultaneous enhancement in Cresyl Violet (acceptor) emission validates and confirms the non-radiative resonance energy transfer from Zn-Cu-In-S/ZnS QDs to Cresyl violet. The values of spectral overlap, Förster distance, the distance between donor and acceptor pair and FRET efficiency were determined using the steady state as well as time-resolved fluorescence spectroscopic techniques. This study demonstrates that this systemexhibits efficient FRET and can act as a very sensitive chemical sensor. Since Zn-Cu-In-S/ZnS QDs are nontoxic compared to popular cadmium-based quantum dots, the application of FRET in biological systems will be advantageous. It can find vast applications in photonics and biomedical applications.

Thermally activated delayed fluorescence in a mechanically soft charge-transfer complex: role of the locally excited state.

Molecular design for thermally activated delayed fluorescence (TADF) necessitates precise molecular geometric requirements along with definite electronic states to ensure high intersystem crossing (ISC) rate and photoluminescence quantum yield (PLQY). Achieving all these requirements synchronously while maintaining ease of synthesis and scalability is still challenging. To circumvent this, our strategy of combining a crystal engineering approach with basic molecular quantum mechanical principles appears promising. A holistic, non-covalent approach for achieving efficient TADF in crystalline materials with distinct mechanical properties is highlighted here. Charge transfer (CT) co-crystals of two carbazole-derived donors (ETC and DTBC) with an acceptor (TFDCNB) molecule are elaborated as a proof-of-concept. Using temperature-dependent steady-state and time-resolved photoluminescence techniques, we prove the need for a donor-centric triplet state (3LE) to ensure efficient TADF. Such intermediate states guarantee a naturally forbidden, energetically uphill reverse intersystem crossing (RISC) process, which is paramount for effective TADF. A unique single-crystal packing feature with isolated D-A-D trimeric units ensured minimal non-radiative exciton loss, leading to a high PLQY and displaying interesting mechanical plastic bending behaviour. Thus, a comprehensive approach involving a non-covalent strategy to circumvent the conflicting requirements of a small effective singlet-triplet energy offset and a high oscillator strength for efficient TADF emitters is achieved here.

Deciphering the ultrafast dynamics of a new tetraphenylethylene derivative in solutions: charge separation, phenyl ring rotation and CC bond twisting.

Tetraphenylethylene (TPE) derivatives are one of the fundamental units for developing aggregation induced emission (AIE) scaffolds. However, the underlying mechanisms implicated in the relaxation of the excited TPE remain a topic of ongoing discussion, while the effect of bulky substituents on its photobehaviour is still under scrutiny. Here, we report a detailed study of the photophysical properties of a new symmetrical and bulky TPE derivative with terphenyl groups (TTECOOBu) in solvents of different polarities and viscosities. Using femto- to nanosecond (fs-ns) time-resolved absorption and emission techniques, we elucidated the role of the phenyl group rotations and core ethylene bond twisting in its behaviour. We demonstrate that TTECOOBu in DCM solutions undergoes a 600 fs charge separation along the ethylene bond leading to a resonance structure with a lifetime of ∼1 ns. The latter relaxes via two consecutive events: a twisting of the ethylene bond (∼ 9 ps) and a rotation of the phenyl rings (∼ 30 ps) leading to conformationally-relaxed species with a largely Stokes-shifted emission (∼ 12 500 cm-1). The formation of the red-emitting species clearly depends on the solvent viscosity and rigidity of the medium. Contrary to the photobehavior in the highly viscous triacetin or rigid polymer matrix of PMMA, a reversible mechanism was observed in DCM and DMF solutions. These results provide new findings on the ultrafast mechanisms of excited TPE derivatives and should help in the development of new molecular rotors with interesting AIE properties for photonic applications.

Synthesis, characterization, luminescence properties and deciphering the role of a terpyridyl-imidazole based ligand in the dissimilar luminescence sensitization of ternary lanthanide(III) tris-(β-diketonate) complexes.

We designed four ternary lanthanide tris-(β-diketonate) complexes of the form [Ln(tta)3(tpy-HImzphen)], where Ln = LaIII, EuIII, SmIII and TbIII; tta = (2-theonyltrifluoroacetonate) and tpy-HImzphen = 2-(4-[2,2':6',2'']terpyridin-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole. All the complexes have been thoroughly characterized by standard analytical tools and spectroscopic techniques including single crystal X-ray diffraction. In situ generation of the complexes was also monitored via absorption and emission spectroscopy upon incremental addition of the respective lanthanide precursor {Ln(tta)3(H2O)2} to the dichloromethane solution of the terpyridyl-imidazole ligand. The photophysical behaviors of all the complexes were thoroughly investigated via absorption and both steady-state and time-resolved emission spectroscopic techniques. The emission spectral measurements were carried out at both room temperature and 77 K to understand the deactivation dynamics of the excited states and elucidate the distinctive luminescence responses from the four lanthanide metal ions owing to the introduction of the terpyridyl-based ancillary ligand.

Fluorescence of Bimolecular Guanine Quadruplexes: From Femtoseconds to Nanoseconds

The paper deals with the fluorescence of guanine quadruplexes (G4) formed by association of two DNA strands d(GGGGTTTTGGGG) in the presence of K+ cations, noted as OXY/K+ in reference to the protozoon Oxytricha nova, whose telomere contains TTTTGGGG repeats. They were studied by steady-state and time-resolved techniques, time-correlated single photon counting, and fluorescence upconversion. The maximum of the OXY/K+ fluorescence spectrum is located at 334 nm, and the quantum yield is 5.8 × 10-4. About 75% of the photons are emitted before 100 ps and stem from ππ* states, possibly with a small contribution of charge transfer. Time-resolved fluorescence anisotropy measurements indicate that ultrafast (<330 fs) excitation transfer, due to internal conversion among exciton states, is more efficient in OXY/K+ compared to previously studied G4 structures. This is attributed to the arrangement of the peripheral thymines in two diagonal loops with restricted mobility, facilitating the interaction among them and with guanines. Thymines should also be responsible for a weak intensity excimer/exciplex emission band, peaking at 445 nm. Finally, the longest living fluorescence component (∼2.1 ns) is observed at the blue side of the spectrum. So far, high-energy long-lived emitting states had been reported only for double-stranded structures but not for G4.

Spatiotemporal Design of the Metal-Organic Framework DUT-8(M).

Switchable metal-organic frameworks (MOFs) change their structure in time and selectively open their pores adsorbing guest molecules, leading to highly selective separation, pressure amplification, sensing, and actuation applications. The 3D engineering of MOFs has reached a high level of maturity, but spatiotemporal evolution opens a new perspective toward engineering materials in the 4th dimension (time) by t-axis design, in essence exploiting the deliberate tuning of activation barriers. This work demonstrates the first example in which an explicit temporal engineering of a switchable MOF (DUT-8, [M1 M2 (2,6-ndc)2 dabco]n , 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4diazabicyclo[2.2.2]octane, M1 = Ni, M2 = Co) is presented. The temporal response is deliberately tuned by variations in cobalt content. A spectrum of advanced analytical methods is presented for analyzing the switching kinetics stimulated by vapor adsorption using insitu time-resolved techniques ranging from ensemble adsorption and advanced synchrotron X-ray diffraction experiments to individual crystal analysis. A novel analysis technique based on microscopic observation of individual crystals in a microfluidic channel reveals the lowest limit for adsorption switching reported so far. Differences in the spatiotemporal response of crystal ensembles originate from an induction time that varies statistically and widens characteristically with increasing cobalt content reflecting increasing activation barriers.

A lanthanide-based high-sensitivity fluorescence method for the on-site rapid detection of thermostable direct hemolysin of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a common foodborne pathogen in seafood, which often causes seafood borne bacterial gastroenteritis or food poisoning. Thermostable direct hemolysin (TDH) is considered to be one of the main virulence factors involved in this pathogen. The most clinical V. parahaemolyticus isolates produce TDH. Therefore, high sensitivity and specificity detection of TDH are of great significance for food safety and early diagnosis of diseases caused by V. parahaemolyticus. In this study, we developed a rapid, sensitive immunochromatographic test paper assay for the quantitative detection of TDH in seafood samples using time-resolved fluorescence techniques. First, we completed the preparation of fluorescent detection antibodies by coupling lanthanide fluorescent nanospheres with homemade high-affinity polyclonal antibodies based on the principle of the double-antibody sandwich. The lanthanide fluorescent nanospheres used in this study are characterized by a large stokes shift and a long fluorescence lifetime, which effectively reduces background noise and improves detection sensitivity. In addition, the method can be completed within 15 min for the detection of TDH, has a detection limit below 50 ng/mL and good linearity in the range of 50–5000 ng/mL. Moreover, it has good specificity and no cross-reactivity with Vibrio vulnificus hemolysin (VVH), Clostridium perfringens α toxin (CPA) or C. perfringens ε toxin (ETX). Finally, the sensitivity of this method was unchanged when the three simulated samples of Patinopecten yessoensis, Ruditapes philippinarum, and Scapharca broughtonii tested, indicating that the method is not affected by samples in a complex matrix. In conclusion, this study establishes a practical new method for on-site rapid detection of TDH, which is easy to operate, fast response, easy to carry and can be implemented under the field conditions without expensive equipment and professional person.

To twist or not to twist: From chromophore structure to dynamics inside engineered photoconvertible and photoswitchable fluorescent proteins.

Green-to-red photoconvertible fluorescent proteins (FPs) are vital biomimetic tools for powerful techniques such as super-resolution imaging. A unique Kaede-type FP named the least evolved ancestor (LEA) enables delineation of the evolutionary step to acquire photoconversion capability from the ancestral green fluorescent protein (GFP). A key residue, Ala69, was identified through several steady-state and time-resolved spectroscopic techniques that allows LEA to effectively photoswitch and enhance the green-to-red photoconversion. However, the inner workings of this functional protein have remained elusive due to practical challenges of capturing the photoexcited chromophore motions in real time. Here, we implemented femtosecond stimulated Raman spectroscopy and transient absorption on LEA-A69T, aided by relevant crystal structures and control FPs, revealing that Thr69 promotes a stronger π-π stacking interaction between the chromophore phenolate (P-)ring and His193 in FP mutants that cannot photoconvert or photoswitch. Characteristic time constants of ~60-67 ps are attributed to P-ring twist as the onset for photoswitching in LEA (major) and LEA-A69T (minor) with photoconversion capability, different from ~16/29 ps in correlation with the Gln62/His62 side-chain twist in ALL-GFP/ALL-Q62H, indicative of the light-induced conformational relaxation preferences in various local environments. A minor subpopulation of LEA-A69T capable of positive photoswitching was revealed by time-resolved electronic spectroscopies with targeted light irradiation wavelengths. The unveiled chromophore structure and dynamics inside engineered FPs in an aqueous buffer solution can be generalized to improve other green-to-red photoconvertible FPs from the bottom up for deeper biophysics with molecular biology insights and powerful bioimaging advances.

Dual emissive carbon dots: Synthesis strategies, properties and its ratiometric sensing applications

Carbon dots (CDs) have received much attention in the field of sensing as fluorescent nanomaterials. They possess simple preparation, excellent optical properties, low toxicity, and brilliant biocompatibility. Photoluminescence in CDs is caused by chemical features, such as graphitic conjugated cores, molecular fluorophores and surface defect states. The emission wavelength of fabricated CDs primarily accumulates single bands in the blue, green or red region. Meanwhile, the structure of CDs and the relationship between their structure and optical properties are still being debated. Apart from that, the existence of single emission bands reduces the efficiency of CDs for sensing multiple analytes in a single process. To overcome this issue, dual conjugated emitters have been designed using carbon dots, quantum dots and metal–organic frameworks. Their fabrication is time-consuming, requires purification and has unequal photostability. It is critical to design and produce nanoprobes with no labeling and intrinsic dual emission. Thus, this review demonstrates the fundamentals to enlighten the PL mechanism for the multi-emissive response in CDs through ultrafast time-resolved and DFT techniques. An attempt is made to provide an in-depth understanding of diversified paths, such as modulation in their interparticle distance, integration of rare-earth metals and metallic to elucidate the duality in their emission spectra. We have provided insights into implementing intrinsic dual emissive CDs in different ratiometric models. Current states, portable challenges, the significance of fabricating CDs with dual emission peaks and their applications are rationally discussed. The main focus of the review is to discuss various methods and parameters to induce different emissions in CDs with single or dual bands rather than the sensing mechanisms. The goal of this review is to describe the theoretical justification for the sensing response of CDs by varying different parameters, such as pH, precursor, etc.

Tuning the Photophysics of Two-Arm Bis[(dimethylamino)styryl]benzene Derivatives by Heterocyclic Substitution.

The identification of novel molecular systems with high fluorescence and significant non-linear optical (NLO) properties is a hot topic in the continuous search for new emissive probes. Here, the photobehavior of three two-arm bis[(dimethylamino)styryl]benzene derivatives, where the central benzene was replaced by pyridine, furan, or thiophene, was studied by stationary and time-resolved spectroscopic techniques with ns and fs resolution. The three molecules under investigation all showed positive fluorosolvatochromism, due to intramolecular charge-transfer (ICT) dynamics from the electron-donor dimethylamino groups, and significant fluorescence quantum yields, because of the population of a planar and emissive ICT state stabilized by intramolecular hydrogen-bond-like interactions. The NLO properties (hyperpolarizability coefficient and TPA cross-section) were also measured. The obtained results allowed the role of the central heteroaromatic ring to be disclosed. In particular, the introduction of the thiophene ring guarantees high fluorescent quantum yields irrespective of the polarity of the medium, and the largest hyperpolarizability coefficient because of the increased conjugation. An important and structure-dependent involvement of the triplet state was also highlighted, with the intersystem crossing being competitive with fluorescence, especially in the thiophene derivative, where the triplet was found to significantly sensitize molecular oxygen even in polar environment, leading to possible applications in photodynamic therapy.

Progress and Perspectives of Spectroscopic Studies on Carbon K-Edge Using Novel Soft X-ray Pulsed Sources

The development of novel coherent and brilliant sources, such as soft X-ray free electron laser (FEL) and high harmonic generation (HHG), enables new ultrafast analysis of the electronic and structural dynamics of a wide variety of materials. Soft X-ray FEL delivers high-brilliance beams with a short pulse duration, high spatial coherence and photon energy tunability. In comparison with FELs, HHG X-ray sources are characterized by a wide spectral bandwidth and few- to sub-femtosecond pulses. The approach will lead to the time-resolved reconstruction of molecular dynamics, shedding light on different photochemical pathways. The high peak brilliance of soft X-ray FELs facilitates investigations in a nonlinear regime, while the broader spectral bandwidth of the HHG sources may provide the simultaneous probing of multiple components. Significant technical breakthroughs in these novel sources are under way to improve brilliance, pulse duration, and to control spectral bandwidth, spot size, and energy resolution. Therefore, in the next few years, the new generation of soft X-ray sources combined with novel experimental techniques, new detectors, and computing capabilities will allow for the study of several extremely fast dynamics, such as vibronic dynamics. In the present review, we discuss recent developments in experiments, performed with soft X-ray FELs and HHG sources, operating near the carbon K-absorption edge, being a key atomic component in biosystems and soft materials. Different spectroscopy methods such as time-resolved pump-probe techniques, nonlinear spectroscopies and photoelectron spectroscopy studies have been addressed in an attempt to better understand fundamental physico-chemical processes.

Recent advances in time-resolved luminescence spectroscopy at MAX IV and PETRA III storage rings

Short-wavelength synchrotron radiation excitation has been an indispensable tool in the studies of the properties of wide gap materials using time-resolved low-temperature luminescence spectroscopy. In recent years, several setups for such investigations have been launched at MAX IV Laboratory and Photon Science at DESY. Two permanently stationed time-resolved luminescence setups at FinEstBeAMS and P66 beamlines are in operation at MAX IV 1.5 GeV and Petra III storage rings, respectively. Mobile luminescence setups have been developed for studies at FemtoMAX and P23 beamlines. FinEstBeAMS, P66 and P23 provide time resolution from ∼160 to 100 ps. The FemtoMAX photon source based on an in-vacuum undulator getting an electron beam from the 3 GeV linear accelerator provides an exceptional time resolution of ∼30 ps, limited by time response of the photodetector. The performance of the setups, achieved milestones and research challenges are discussed for four new luminescence stations available for the research community with the main focus on time-resolved techniques.

Vortex-induced vibration of a two degree-of-freedom flexibly mounted circular cylinder in the crossflow direction

Vortex-induced vibration (VIV) of a two degree-of-freedom (DOF) circular cylinder, placed in the test section of a recirculating water tunnel and free to oscillate in its first two vibrational modes in the crossflow direction, is studied experimentally. The dynamic response of the cylinder is studied for a reduced velocity range of $U^*=4\unicode{x2013}30$ for eigenfrequency ratios in the range of 1.3–3.0. For the two DOF system, while the onset of the VIV response followed a similar lock-in region as those observed for a classical VIV response of a single DOF system, by increasing the reduced velocity a secondary lock-in region was observed over which the oscillations of the cylinder were locked into the system's second mode. In addition, there existed an intermediate range of reduced velocity over which the VIV response consisted of oscillations at a combination of the first two natural modes of the system. As the eigenfrequency ratio between the first two modes increased, the secondary lock-in range was extended to higher reduced velocities and the reduced velocity range over which multi-modal oscillations were observed was decreased. A full map of vortex dynamics in the wake of the cylinder was developed qualitatively and quantitatively using hydrogen bubble flow visualization and time-resolved volumetric particle tracking velocimetry techniques, respectively. A Q-criterion analysis revealed the existence of highly three-dimensional vortex structures in the wake of the cylinder. The spatiotemporal mode analysis using the proper orthogonal decomposition technique revealed strong coupling between the vortex shedding modes in the wake of the cylinder and the structural vibration modes.

Recent Development of Ultrafast Optical Characterizations for Quantum Materials.

The advent of intense ultrashort optical pulses spanning a frequency range from terahertz to the visible has opened a new era in the experimental investigation and manipulation of quantum materials. The generation of strong optical field in an ultrashort time scale enables the steering of quantum materials nonadiabatically, inducing novel phenomenon or creating new phases which may not have an equilibrium counterpart. Ultrafast time-resolved optical techniques have provided rich information and played an important role in characterization of the nonequilibrium and nonlinear properties of solid systems. Here, some of the recent progress of ultrafast optical techniques and their applications to the detection and manipulation of physical properties in selected quantum materials are reviewed. Specifically, the new development in the detection of the Higgs mode and photoinduced nonequilibrium response in the study of superconductors by time-resolved terahertz spectroscopy are discussed.

Visualizing Intramolecular Dynamics of Membrane Proteins

Membrane proteins play important roles in biological functions, with accompanying allosteric structure changes. Understanding intramolecular dynamics helps elucidate catalytic mechanisms and develop new drugs. In contrast to the various technologies for structural analysis, methods for analyzing intramolecular dynamics are limited. Single-molecule measurements using optical microscopy have been widely used for kinetic analysis. Recently, improvements in detectors and image analysis technology have made it possible to use single-molecule determination methods using X-rays and electron beams, such as diffracted X-ray tracking (DXT), X-ray free electron laser (XFEL) imaging, and cryo-electron microscopy (cryo-EM). High-speed atomic force microscopy (HS-AFM) is a scanning probe microscope that can capture the structural dynamics of biomolecules in real time at the single-molecule level. Time-resolved techniques also facilitate an understanding of real-time intramolecular processes during chemical reactions. In this review, recent advances in membrane protein dynamics visualization techniques were presented.

Through the Lens of a Momentum Microscope: Viewing Light-Induced Quantum Phenomena in 2D Materials.

Van der Waals (vdW) materials at their 2D limit are diverse, flexible, and unique laboratories to study fundamental quantum phenomena and their future applications. Their novel properties rely on their pronounced Coulomb interactions, variety of crystal symmetries and spin-physics, and the ease of incorporation of different vdW materials to form sophisticated heterostructures. In particular, the excited state properties of many 2D semiconductors and semi-metals are relevant for their technological applications, particularly those that can be induced by light. In this paper, the recent advances made in studying out-of-equilibrium, light-induced, phenomena in these materials are reviewed using powerful, surface-sensitive, time-resolved photoemission-based techniques, with a particular emphasis on the emerging multi-dimensional photoemission spectroscopy technique of time-resolved momentum microscopy. The advances this technique has enabled in studying the nature and dynamics of occupied excited states in these materials are discussed. Then, the future research directions opened by these scientific and instrumental advancements are projected for studying the physics of 2D materials and the opportunities to engineer their band-structure and band-topology by laser fields.

Combination of ultrafast time-resolved spectroscopy techniques for the analysis of electron dynamics of heliumlike impurity centers in silicon

Helium-like interstitial donors in silicon have larger binding energies compared to their hydrogen-like counterparts. Long lifetimes of the excited states are expected since one-phonon transitions are not available. Here, the authors study their relaxation dynamics at two different free electron laser facilities using photon echo, transient grating, and pump-probe spectroscopy. In contrast to the theoretical predictions and previous experimental studies, it is found that the relaxation rates are extremely high. These results shed new light on the electron-lattice interaction and open the possibility for further studies of similar materials.

Rare earth effect on laser produced plasma dynamics during pulsed laser deposition of doped cobalt ferrite

The addition of rare earth elements the ferrites can lead to significant changes in structural, magnetic and electric properties of bulk materials and also of thin films deposited by pulsed laser deposition. The present study relies on the analysis of the laser induced plasma of three sets of cobalt ferrite targets doped with various concentrations of RE elements (Dy, Gd, Yb) and proposes a correlation of the derived results with structural investigations of the films obtained during the same experiment. ICCD imaging and space-and time-resolved optical emission spectroscopy techniques were used to obtain information on the dynamics and excitation temperatures of various species found in the laser produced plasmas (LPP). Initial investigations on the global behavior of the LPP revealed that the addition of RE reduced the drift velocities of the formed plasma structures, the lowest ones being observed for the targets doped with the heaviest RE (Yb). Space-and time-resolved spectroscopy measurements applied for all main elements (Fe, Co and RE - both neutral and ionic species) showed a complex dynamic system, with decreased/increased kinetic energies for neutrals/ions at high dopant concentrations, suggesting a possible re-sputtering effect at the films surface. The individual excitation temperatures of the main elements derived from Boltzmann plots increased as the RE content was augmented via radiative collision events due to their larger diameters compared with Co, Fe or O. The spatial distribution of electron temperature can be explained by the charge separation occurring with the addition of RE in the investigated systems.

Inhibition of advanced glycation end products and protein oxidation by leaf extracts and phenolics from Chilean bean landraces

• Leaf extracts from six Chilean landraces of Phaseolus vulgaris were investigated. • Some 26 compounds were identified from the most active sample by HPLC-MS/MS. • Pearson’s analysis shows strong correlations between phenolics and AGEs inhibition. • Caffeoyl malic acid and rutin synergistically inhibit AGEs and protein oxidation. Phenolics can decrease the levels of advanced glycation end products (AGEs) from proteins, but their mechanisms in complex mixtures are poorly understood. Leaf extracts and the main phenolics from Chilean bean ( Phaseolus vulgaris ) landraces were assessed for their capacity to inhibit AGEs and oxidative modifications on bovine serum albumin incubated with glucose. The leaf extracts of six bean landraces decreased AGEs (fluorescent AGEs and carboxymethyl lysine) and oxidative (Kyn, Di-Tyr, protein carbonyls) modifications. Fluorescent AGEs were characterized by time-resolved techniques. The composition of the extracts was determined by HPLC-DAD-Q-TOF-MS/MS, and the main compounds were quantified by HPLC. Correlations between the levels of AGEs or protein carbonyls with the main phenolics suggested synergic effects of caffeoyl malic acid (CMA) and rutin. The synergic effect was evaluated using mixtures of rutin and CMA, showing a strong decrease in fluorescent AGEs and protein carbonylation compared with the pure single compounds, supporting this finding.

Dynamics of hydrogen bond reorganization in the S1(ππ*) state of 9-Anthracenecarboxaldehyde

Effect of solvent polarity and hydrogen bonding interaction on the excited state dynamics of 9-Anthracenecarboxaldehyde (9-ACD) have been investigated using steady state and time-resolved electronic and vibrational spectroscopic techniques. Photophysical properties and dynamics of the excited states are seen to be more sensitive to intermolecular hydrogen bonding ability of the solvent, rather than its polarity. FTIR studies reveal formation of complexes with the protic solvents via formation of conventional hydrogen bond at the carbonyl site of 9-ACD molecule. In strong hydrogen bond donating solvents, namely, 2, 2, 2-trifuoroethanol (TFE) and 1, 1, 1, 3, 3, 3-hexafluoroisopropanol (HFIP), nearly all the molecules of 9-ACD in solution remain engaged in complex formation leaving insignificant number of molecules remaining free in solution. In aprotic solvents, the S1 state is short-lived (the lifetime is only a few tens of ps) and intersystem crossing (ISC) is the major deactivation pathway (the triplet yield is near unity). However, in strong hydrogen bond donating solvents, the S1 state lifetime is long (a few ns) because the deactivation pathway for the S1 state via the triplet manifold is blocked. Both the ultrafast time-resolved electronic and vibrational spectroscopy studies in TFE and HFIP reveal that hydrogen bond reorganization process following photoexcitation of the hydrogen bonded complex is the only relaxation process undergone by the S1 state in sub-100 ps time domain. However, the time-resolved IR (TRIR) spectroscopy studies further reveal the possibility of formation of aromatic π- hydrogen bonding and reorganization of the hydrogen bond at this site makes the major contribution towards the S1 state relaxation process in strong hydrogen bond donating solvents.