A	Absorbance at irradiation wavelength
Bipy	2,2′-bipyridine
BODIPY	4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene
CT	Charge transfer
CycHex	Cyclohexane
DCM	Dichloromethane
DFT	Density functional theory
DIPY	Heteroleptic p-block mono(dipyrrinato) complex
DPM	Dipyrromethene
EnT	Energy transfer
F	Fraction of light absorbed
HSO	Spin–orbital Hamiltonian
HAE	Heavy atom effect
Hex	Mixture of hexanes
MCH	Methylcyclohexane
HOMO	Highest occupied molecular orbital
HOMO-1	MO level one step lower in energy than the HOMO
I	Integrated emission intensity
I 0	Light intensity of the irradiation source
IC	Internal Conversion
1,3IL	Singlet or triplet intraligand state
1,3ILCT	Singlet or triplet intraligand charge transfer state
ISC	Intersystem crossing
$k_f$	Fluorescence rate constant
$k_{ISC}$	Intersystem crossing rate constant
$k_{nr}$	Nonradiative rate constant; $k_{nr}=k_{ISC}+k_{IC} \approx k_{IC}$
$k_p$	Phosphorescence rate constant
$k_q$	Bimolecular quenching constant
$k_r$	Radiative rate constant; $k_r=k_f+k_p \approx k_f$
$K_{SV}$	Stern-Volmer constant
1,3LLCT	Singlet or triplet ligand-to-ligand charge transfer, also called ICT state
1,3LMCT	Singlet or triplet ligand-to-metal charge transfer
LUMO	Lowest unoccupied molecular orbital
LUMO + 1	MO level one step higher in energy than the LUMO
1,3MC	Singlet or triplet metal-centered
MeOH	Methanol
Mes	Mesityl
1,3MLCT	Singlet or triplet metal-to-ligand charge transfer state
1,3MMCT	Singlet or triplet metal-to-metal charge transfer state
MO	Molecular orbital
MOF	Metal-organic framework
n	Refractive index
NIR	Near-infrared region
PDT	Photodynamic therapy
Ph	Phenyl
PS	Photosensitizer
Q	Quencher (= 3O2 in PDT)
QY	Quantum yield, see φ
r3	Mean cubic radial distribution of the electron
ROS	Reactive oxygen species
SBCT	Symmetry breaking charge transfer
SOC	Spin–orbital coupling
S0	Singlet ground state
S1	First singlet excited state
TA	Transient absorption
TDDFT	Time dependent DFT
THF	Tetrahydrofuran
TM	Transition metal
Tol	Toluene
TTA	Triplet-triplet annihilation
T1	First triplet excited state
UV-Vis	Ultra-violet – visible range
Z	Atomic number
∆λ	Stokes shift in nm
∆ES1−T1	Energy gap between the first triplet excited state and the first singlet excited state
∆ET1−S0	Energy gap between the first triplet excited state and the ground state
∆ṽ	Stokes shift in cm−1
∆ṽ0	Uncorrected Stokes shift in cm−1, obtained from eq. Equation (6)
ɛ	Molar absorption coefficient
λ	Wavelength (in cm−1)
λa	Wavelength at maximum absorption
λex	Excitation wavelength
λf	Wavelength at maximum emission
τ	Lifetime of a state
τ0	Lifetime in the absence of Q
τr	Radiative lifetime
τS	Singlet state lifetime
τT	Triplet state lifetime
$\mathsf{\phi }$	Quantum yield (QY)
${\mathsf{\phi }}_{\Delta }$	Singlet oxygen quantum yield
${\mathsf{\phi }}_f$	Fluorescence quantum yield
${\mathsf{\phi }}_{ISC}$	Intersystem crossing quantum yield
${\mathsf{\phi }}_T$	Quantum yield of triplet formation