Polarized two‐photon fluorescence excitation studies of pyrimidine

Two‐photon fluorescence excitation studies are reported for pyrimidine (1, 3‐diazine) dissolved in a hexane solution at room temperature. Quantitative two‐photon absorption strengths for the three lowest electronic absorption bands are measured relative to the benzene B2u ← A1g two‐photon transition. The B1(nπ*) ← A1 excitation profile matches the one‐photon absorption band closely, indicating an allowed two‐photon transition. However, the B2(ππ*) two‐photon intensity is vibronically induced by a 1600 cm−1 b2 vibration, even though transitions into this state are formally two‐photon allowed. In addition, polarization analysis is used to uncover a new transition in pyrimidine in a region of overlapping absorptions. This new transition is assigned to the lowest A2(nπ*) state. If this assignment is correct, the A2(nπ*), B1(nπ*) splitting is 1.4 eV. Spectroscopic CNDO and INDO calculations of the two‐photon absorption strengths are also reported.

[1]  W. M. McClain,et al.  Complete Polarization Study of the Two‐Photon Absorption of Liquid 1‐Chloronaphthalene , 1972 .

[2]  T. Yonezawa,et al.  Semi-empirical molecular orbital calculations the electronic structure and the spin-orbit coupling in azabenzenes , 1969 .

[3]  H. Shull,et al.  On the Application of the Molecular Orbital Method to the Spectra of Substituted Aromatic Hydrocarbons , 1957 .

[4]  Michael C. Zerner,et al.  An intermediate neglect of differential overlap technique for spectroscopy: Pyrrole and the azines , 1973 .

[5]  W. M. McClain.  Excited State Symmetry Assignment Through Polarized Two‐Photon Absorption Studies of Fluids , 1971 .

[6]  B. Dick,et al.  Two-photon spectroscopy of dipole-forbidden transitions , 1979 .

[7]  E. C. Lim,et al.  Radiationless transitions in monocyclic diazines , 1971 .

[8]  D. Whiffen.  The force field, vibration frequencies, normal co-ordinates, infra-red and Raman intensities for benzene , 1955, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[9]  Si Chen,et al.  Calculations of singlet and triplet states of some azabenzenes by modified INDO-CI , 1973 .

[10]  P. J. Wheatley.  The crystal and molecular structure of pyrimidine , 1960 .

[11]  A. C. Albrecht,et al.  Vibronic calculations in benzene by CNDO/S , 1974 .

[12]  M. El-Sayed,et al.  The low energy two-photon spectrum of pyrazine using the phosphorescence photoexcitation method , 1975 .

[13]  R. Rava,et al.  Vibronic mechanisms in the two‐photon spectrum of benzene , 1981 .

[14]  O. S. Mortensen,et al.  Initial and final molecular states as ‘‘virtual states’’ in two‐photon processes , 1981 .

[15]  E. C. Lim,et al.  Triplet–triplet absorption of pyrazine related to the n+π* (B3u)–n−π* (B2g) splitting , 1980 .

[16]  R. Rava,et al.  Two‐photon spectra of substituted benzenes , 1981 .

[17]  H. Jaffe,et al.  The use of CNDO in spectroscopy. XV. Two photon absorption , 1980 .

[18]  R. L. Ellis,et al.  The use of the CNDO method in spectroscopy , 1972 .

[19]  B. Dick,et al.  Two‐photon spectroscopy of dipole‐forbidden transitions. II. Calculation of two‐photon cross sections by the CNDO–CI method , 1979 .

[20]  T. W. Scott,et al.  A Rydberg transition in benzene in the condensed phase: Two-photon fluorescence excitation studies , 1981 .

[21]  E. C. Lim,et al.  Proximity effect in spin sublevel dynamics: Possible influence of a low-lying3 A2 (nπ*) state: On singlet → triplet intersystem crossing of Pyrimidine , 1979 .

[22]  K. Innes,et al.  Electronic states of azabenzenes: A critical review , 1967 .